Chapter 9

PHYLUM PLATYHELMINTHES

 

 

9.1 THE CESTODES

9.1.1 GENERAL INFORMATION

9.1.1.1 Classification of Medically Important Cestodes

Phylum: Platyhelminthes

Class: Cestoda (Eucestoda - the true tapeworms,

Cotyloda - the ("pseudotapeworms")

Order: Pseudophyllidea Cyclophyllidea

 

9.1.1.2 Terms Used in Relation to Cestodes (See Figures 3.18 and 3..19 for selected diagrams)

Rostellum

The protuberant anterior part of the scolex of certain tapeworms.

Scolex

The anterior organ of a tapeworm used for attachment to host tisues. Also known as the holdfast.

Bothrium

A longitudinal groove in the scolex of pseudophyllidenas.

Neck

The connecting tissues between the scolex and strobila of a tapeworm. The part is unsegmented.

Proglottid

Single segment of a tapeworm

Strobila

The body of a tapeworm

Strobilisation

The process of producing or growing new segments (proglottids). This happens near the neck region.

Protoscolex

The scolex of a larval stage. Morphologically it resembles the adult scolex.

Hexacanth

A larval stage of the tapeworm having 6 hooks

Oncosphere

A hexacanth embryo

Coracidium

A ciliated oncosphere which develops in the ova of pseudophyllidea.

Procercoid

The second stage larva of pseudophyllidea which bears 6 hooks near the posterior end. 

Plerocercoid

The third stage larva of pseudophyllidea which has a solid body.

 Figure 3.18: Ther Morphology of Costodes

Hydatid

Larval stage of Echinococcus, generally containing a large number of protoscoleces.

Hydatid sand

Free protoscoleces lying inside a hydatid.

Multilocular hydatid

Larval stage of Echinococcus multilocularis in which exogenous development occurs resulting in infiltration of tissues.

Cysticercus

A larval form of a tapeworm having fluid filled bladder.

Cysticercoid

A larval form of a tapeworm which has a solid body and no bladder. 

Figure 3.19: Ther Morphology of Costodes

 Daughter cyst

A cyst formed by endogenous or exogenous budding from the germinal layer of a hydatid.

Endogenous budding

Inward development from the germinal layer of a larval cestode.

Brood capsule

A small cyst attached to the germinal layer of the hydatid, containing many protoscoleces.

Egg capsule

A membranous structure containing eggs of a tapeworm, in the absence of a uterus.

 

9.1.1.3 Basic Information 

9.1.1.3.1 General Morphology (See figure 3.20 and 3.21)

  • 1. Tapeworms are hermaphroditic
  • 2. They are endoparasites. Adult tapeworms are always found in the gastrointestinal tract of their definitive hosts. Larval tapeworms may be found in a variety of extraintestinal sites.
  • 3. They lack a body cavity.
  • 4. They lack an alimentary tract. Tapeworms take in nutrients by absorbing them through their tegument. 
  • 5. There is a great variation in the sizes of tapeworms, from a few mm (almost microscopic) up to several meters in length.
  • 6. The body of a tapeworm consists of:
    • a. A head or Scolex. Ths scolex is usually round. It normally has four suckers (acetabula). The scolex may be either armed or unarmed. A scolex is said to be armed if it possesses hooks or rostellum with hooklets. A rostellum is a rectractible nose which may be covered with posteriorly facing hooklets. If neither hooks nor an armed rostellum is present, the entire scolex is said to be unarmed.
    • b. A short unsegmented Neck.
    • c. The remainder of the body is called the Strobila. The strobila is made up of a number of segments called Proglottids. (See Figure 3.21) Each proglottid usually contains one or two sets of reproductive organs. Proglottids are formed from the neck and mature as they are pushed away from the scolex. There are three basic types of proglottids:

      1) Immature Proglottids.

      • These proglottids are most proximal in the tapeworm chain. They are closest to the neck. These proglottids contain immature reproductive organs. The reproductive organs are not functional. 

    Figure 3.20 Cestode Morphology

    Figure 3.21 Cestode Morphology

 2) Mature proglottids.

  • These proglottids are farther down the tapeworm "chain". These mature proglottids contain fully mature reproductive organs that are fully functional.

3) Gravid proglottids.

  • These proglottids are the most distal in the tapeworm "chain". In these proglottids, the reproductive orgas have degenerated, leaving a proglottid which is filled by a uterus completely distended with eggs. Gravid proglottids are detached and pass out of the host singly or are occasionally passed out linked together in chains. The eggs of the tapeworm are then set free by disintegration of the gravid proglottids. Sometimes, however, eggs will be released by internal pressure within the tapeworm’s uterus.
  • 7. With regard to the organ systems of cestodes:
    • a. The body is covered by a tegument. The tegument acts as an absorptive structure. The tapeworm absorbs its nutrients through its tegument.
    • b. There is no digestive tract.
    • c. Muscles lie beneath the tegument and more deeply in the parenchyma-filled body.
    • d. A complete excretory system is present within each proglottid.
    • e. A nervous system is present.
    • f. A reproductive system is present. As mentioned previously, there are one or two sets of reproductive organs (both male and female) per proglottid. Tapeworms like flukes, are hermaphroditic. The reproductive organs generally mature from the anterior to the posteriorproglottids (see previous section under proglottids). Remember, there are both male and female reproductive organs in every proglottid. 

9.1.1.3.2 Developmental Stages in the Life Cycle of Tapeworms

  • 1. The egg. The fully embryonated egg is called an oncosphere. The oncosphere is bilaterally symmetrical, spherical or oval and is armed with three pairs of hooks. The oncosphere is contained in an envelope called the embryophore. The egg is ingested by the intermediate host, and the oncosphere is released from the embryophore in the intestine of the intermediate host. The oncosphere penetrates the itnestinal mucosa and migrates to its site of predilection via the circulatory system.

 Figure 3.21 Cestode Morphology

  • 2. Cestode life cycles require the development of a larval stage called Mestacetode, which occurs in intermediate hosts. The common forms of larval tapeworm are as follow:

    a. Cysticercoid:

    • A larval tapeworm with a single noninvaginated scolex withdrawn into a small vesicle with practically no cavity. Cysticerocoids will always be found in invertebrates.

    Note: A cysticercus and a cysticercoid are not synonymous terms

    b. Coenurus (sa-NUR-us):

    • A large fluid containing bladder with a number of invaginated scolices attached to the wall.

    c. Hydatid Cyst:

    • A large fluid-containing bladder which develops other cysts called brood capsules in which the scolices develop.

There are other developmental forms of metacestodes which occur in the life cycles of domestic animals. These terms include procercoid, plerocercoid, tetrathyridium and strobilocercus. These terms will be covered when the tapeworms that utilize these metacestodes in their life cycles are discussed.

The metacestode stage is found within an intermediate host. The definitive host ingests the infected intermediate host containing the metacestode stage. The scolex excysts or evaginates, as required, and attaches to the mucosa of the intestine. The scolex will produce a neck and the neck will produce the proglottids.

 Figure 3.23 Some Variations in the life Cycle of Cestodes

9.2 CLASS EUCESTODA OR TRUE TAPEWORMS

9.2.1 GENERAL INFORMATION

I. Tapeworms included in this class which will be studied include:

II. General characteristics of this class:

 

9.3 Order: Cyclophyllidae Family: Anoplocephalidae

9.3.1 ADULT TAPEWORMS FOUND IN THE GASTROINTESTINAL TRACT OF LARGE ANIMALS

A. This group of tapeworms has several qualities in common:

  • 1. The scolices of these tapeworms do not possess a rostellum or hooks. They are said to be unarmed tapeworms. Suckers are present, however.
  • 2. Their proglottids are usually wider than long and each proglattid possesses one or two sets of genital organs. The genital pores are along the margins of the proglottids. 
  • 3. Each egg has three coverings. It is the innermost covering which is important. This innermost membrane is pear-shaped and bears on one side a pair of hooked projections. This innermost membrane is called the PYRIFORM APPARATUS. 
 
  • 4. This first group of tapeworms will utilize some larger animal as the definitive host. Adult tapeworms will be found in the gastrointestional tract of large animals. The metacestodes (larval forms) of these tapeworms will be found in invertebrates in the form of CYSTICERCOIDS.

B. The tape worms with these characteristics in common are:

  • Anoplocephala magna
  • Anoplocephala perfoliata
  • Paranoplocephala mamillana
  • Moniezia benedini
  • Moniezia expansa
  • Thysanosoma actinoides

 

9.3.2 ANOPLOCEPHALA MAGNA, ANOPLOCEPHALA PERFOLIATA, PARANO-PLOCEPHALA MAMILLANA

9.2.3.1 Host and Habitat

These are tapeworms of horses and donkeys.

9.2.3.2 Identification

1. Anaplocephala perfoliata

  • This tapeworm is the most common horse tapeworm. It is seen in the large and small intestine and may occur in large groups near the ileocecal valve.Adults are 5 to 8 cm. in length and 1.2 cm. in width. The scolex is small (2-3 mm. in diameter) and has a "lappet" behind each sucker. The eggs have an egg with a pyriform apparatus and are from 65 to 80 microns in size.

2. Anoplocephala magna

  • Occurs in the small intestine, particularly the jejunum and rarely the stomach. It may reach 80 cm in length and 2.5 cm in width. It is called "magna" because it has a large scolex. Its scolex lacks "lappets". The eggs have a pyriform apparatus and are form 50 to 60 microns in size.

3. Paranoplocephala mamillana

  • This tapeworm occurs in the small intestine and occasionally the stomach. It is a dwarf tapeworm - it is only 5 to 50 by 4 to 6 mm in size. The scolex is narrow. "Lappets" are absent. The eggs are 51 by 37 microns and have a "pyriform apparatus".

 

 

9.2.3.3 Life cycle of the equine tapeworms

Free-living oribatid mites (grain mites) serve as the intermediate hosts. These mites ingest the tapeworm egg containing the pyriform apparatus. A cysticercoid will be produced in the orbatid mite. Infected mites are ingested on herbage and adult tapeworms will be found in the intestine in 4 to 6 weeks.

9.2.3.4 Pathogenesis

Light infections of horse tapeworms produce no clinical signs. Large numbers however may cause ill health, unthriftiness, and Death.

Anoplocephala perfoliata tends to localize in large numbers at the ileocecal valve. It produces small, dark depressed ulcerative lesions where the scolex attached to the cecal wall. This area may be edmatous and demonstrate excessive granulation tissue. Perforation of the intestine may occur.

Anoplocephala magna in large numbers may cause a catarrhal or hemorrhagic enteritis. Perforation of the intestine has been reported.

Paranoplocephala mamillana the dwarf tape worm; seldom causes ill health.

9.2.3.5 Diagnosis

Tapeworm segments may be found in horse feces.

Remember: eggs of all three equine tapeworms possess the characteristic pyriform apparatus.

 

9.2.3.6 Treatment

  • Micronized mebendazole 15 to 20 mg/kg
  • Bithionol 7mg/kg
  • Niclosamide 88 mg/kg
  • Kamala
  • Dichlorophen

9.2.3.7 Control

Oribatid (grain) mites occur widespread on pastures. They are impossible to control.

 

9.3.3 MONIEZIA EXPANSA, MONIEZIA BENEDINI

9.3.3.1 Host and Habitat

M. expansa occurs in the intestinal tract of sheep, goats and cattle while M. benedini occurs in the intestine of cattle.

9.3.3.2 Identification

Both species occur in the small intestine, are large tapeworms (up to 600 cm) and have segments that are wider than long. They have an unarmed scolex, but prominent suckers are present. The species will differ in their segments. At the posterior border of each proglottid of Moniezia expansa, there is a row of rosette-like interproglittidal glands which extend across the width of the proglottid. Moniexia benedini has interproglittidal glands arranged in a short, continous row near the midline of the segment. The eggs of M. expansa are square-shaped, contain a pyriform apparatus, and are up to 75 microns in diameter.

 

 

9.3.3.3 Life Cycle (See figure 3.25)

Proglottids and eggs are passed in the feces. Proglottids resemble cooked rice grains. The tapeworm eggs are ingested by oribated (grain) mites and they develop to cysticercoids within these mites. Ruminants are infected by ingesting infected mites with herbage. The prepatent period is 37 to 40 days.

 

Figure 3.25: Life Cycle of Moniezia Spps. 
 

 

9.3.3.5 Pathogenesis and Clinical Signs

Moniezia is quite prevalent in lambs, kids and calves under six months of age. Light infections with Moniezia spp. are of little importance, but there is a disagreement among parasitologists concerning heavy infections. Workers in the US have not been able to detect any serious effects even from heavy burdens. One may observe that the intestine is a solid mass of tapeworms. They may cause diarrhea and unthriftiness. Obstruction of the intestine has been reported.

9.3.3.6 Diagnosis

Proglottids and eggs are found in the feces. Proglottids resemble cooked rice grains. Eggs are square-shaped or triangular and possess a pyriform apparatus.

9.3.3.7 Treatment

9.3.3.8 Control

Treat animals in the late spring or early summer. If necessary, treat again in the autumn. Infected mites on pasture can be controlled by plowing and reseeding pasture or by rotating pastures.

9.3.4 THYSANOSOMA ACTINOIDES, THE FRINGED TAPEWORM

9.3.4.1 Host and Habitat

This tapeworm has been found in bile ducts, pancreatic ducts and small intestines of sheep, cattle and deer. It is a common parasite in the western part of the US (west of the Mississippi River).

9.3.4.2 Identification

This tapeworm is often found in the bile ducts. It is up to 30 cm long and 8 cm wide. It may be identified by its short segments which bear a posterior "fringe", hence the name, "fringed tapeworm". Each segment possesses two sets of genital organs. Eggs are up to 12 microns in diameter. Eggs do not possess a pyriform apparatus.

 

 

9.3.4.3 Life Cycle

Researchers have found that cysticercoids will develop in psocids (bark lice). It was not possible, however, to induce infection in cattle or sheep using these infected psocids. The complete life cycle is still unknown.

9.3.4.4 Pathogenicity and Clinical Signs

This tapeworm may partially obstruct the flow of bile and pancreatic juice and cause digestive disorders and unthriftiness. Some inflammation of the biliary epithelium has been observed. Enlargement of the bile duct with marked fibrosis and hyperplasia of the wall may be seen. The tapeworm does not appear to have a negative effect on the growth rate of lambs. The presence of this parasite causes condemnation of livers at meat inspection.

9.3.4.5 Diagnosis

Demonstration of segments on fecal flotation.

9.3.4.6 Treatment

9.3.4.7 Control

Treat animals in the late spring or early summer. Retreat in the autumn if needed. Infected bark lice on pasture can be controlled by rotating pastures or plowing and reseeding pasture.

9.4 Order: Cyclophyllidae, Family: Dilepididae

In this family the rostellum is usually provided with hooks, but the suckeres may or may not be unarmed. Genital organs are single or double. The testes are numerous. The uterus may be sac-like or branched and persist or the eggs pass into parenchymatous capsules or paruterine organs.

9.4.1 DIPYLIDIUM CANINUM - THE DOUBLE PORED TAPEWORM, THE CUCUMBER SEED TAPEWORM(See figure 3.26)

9.4.1.1 Host and Habitat

This tapeworm may be found in the small intestine of the dog, cat, fox and occasionally man (primarily children) 

Figure 3.26: Dipylidium Caninum

9.4.1.2 Identification

This tapeworm is found within the small intestines of its definitive host. It is up to 50 cm long. The retractable rostellum bears three to four rows of rosethorn-shaped hooks. Each proglottid contains from 20 to 30 egg packets. Mature and gravid proglottids have in elongate oval shape and resemble cucumber seeds.

9.4.1.3 Life Cycle

The gravid proglottids are voided in the feces or they may leave the host spontaneously and crawl about actively disseminating the eggs. The intermediate hosts are fleas (Ctenocephalides canis, C. felis or Pulex irriitans), or the dog louse (Trichodectes canis). The egg is ingested by the adult louse or by flea larvae. Cysticercoids develop in the arthropods. The definitive host becomes infected by ingesting the infected arthropod.

9.4.1.4 Pathogenesis and Clinical Signs

Normally, adult D. caninum are not very harmful to dogs and cats However, heavy infections may cause nonspecific abdominal signs, especially in small animals. the animal may exhibit diarrhea or constipation or demonstrate an unthrifty pot-bellied appearance. Gravid proglottids may migrate out of the ana, sphincter and be found in the perianal area. This irritation may cause the dog to "scoot"; you can see a similar clinical sign due to a pruritic anus or due to impacted anal glands. The proglottids may also drop off the animal and crawl over chairs, clothes and floors for some minutes. The animal’s bedding is a frequent site for finding the proglottids. The owner does not appreciate these "crawlies".

9.4.1.5 Diagnosis

Identifiaction of cucumberseed-like, double-pored segments crawling on the stool or dried on the perianal hair. Tapeworm egg packets may be found on fecal examination if proglottids have broken.

9.4.1.6 Treatment

The following anthelmintics are available for treatment of D. caninum in dogs and cats:

  • Arecoline hyudrobromide
  • Dichlorophen
  • Niclosamide
  • Praziquantel.

9.4.1.7 Control

Fleas and lice should be eliminated from kennels and catteries to control D. caninum. Maintain good sanitation 

 

9.5 Order: Cyclophyllidae, Family: Taeniidae

9.5.1 THE TAENIID TAPEWORMS

I. The Basics of the Taeniid Tapeworms (See figure 3.27)

Taenia saginata

Taenia solium

Taenia hydatigena

Taenia ovis

Taenia pisiformis

Taenia taneiaformis

Echinococcus granulosus

Echinococcus multilocularis

Multiceps serialis

Multiceps multiceps

9.5.2 TAENIID TAPEWORMS OF MAN

9.5.2.1 TANEIA SAGINATA, THE BEEF TAPEWORM OF MAN

9.5.2.1.1 Host and Habitat

The adult tapeworm is found in the small intestine of man. Man is the only definitive host. The metacestode (or larval bladderworm stage) is a cysticercus and it is found in the skeletal and cardiac muscle (and also fat and visceral organs) of cattle and other ruminants. This metacestode stage has a scientific name, Cysticercus bovis.

9.5.2.1.2 Identification

The adult worm is 4 to 8 meters (rarely up to 25 m) long. The scolex has four suckers and is without a rostellum or hooks. This is an unarmed taeniid tapeworm. The oval eggs are 46 to 50 by 39 to 41 microns. The uterus of a gravid proglottid has 14 to 32 lateral branches and contains about 80,000 eggs. The number of branches may be used to distinguish between T. saginata and T. solium, which is also a parasite of man. This method may be unreliable. The best method for distinguishing the two is to note the absence of an armed rostellum in T. saginata.

9.5.2.1.3 Life Cycle

About ten gravid proglottids are shed daily in the feces, or they migrate out of the anus of man. These are motile proglottids. The eggs will remain viable for several weeks or months in sewage, in rivers and on pastures. In the past in the US, there have been epizootics of bovine cysticercosis in feedlots. These epizootics were caused by infected workers defecating in silos, irrigation ditches and hayfields. Sewage will also spread the eggs. Eggs can pass through sewage treatment plants and be released into rivers. Sewage sludge may be placed on pastures.

The eggs are ingested by cattle. The eggs hatch in the intestine and release the oncosphere. The oncosphere penetrates the intestinal mucosa and reaches the general circulation. The embryos are disseminated throughout the body and cysticerci develop in skeletal and cardiac muscle; they may also be in fat and other organs. In the past, the muscles of predilection were the masseters, heart, diaphragm and tongue. Uusally the cysticerci are spread throughout themusculature. The cysticercus is called Cysticercus bovis. It becomes infective in about 10 weeks and remains viable for up to 9 months. The cysticercus is within a tissue capsule. The presence of cysticerci in beef is called "measly beef". Man is infected by ingestion of raw or undercooked measly beef. Gravid proglottids begin to be passed by man approximately 100 days after infection. Cysticerci begin to degenerate 4 to 6 months after infection. By nine months, a large number may be dead.

9.5.2.2 TAENIA SOLIUM, THE PORK TAPEWORM OF MAN

9.5.2.2.1 Host and Habitat

The adult tapeworm occurs in the small intestine of man. The metacestode or larval stage is a cysticercus and it is found in the skeletal and cardiac muscles of the pig. These metacestodes are called Cysticercus cellulosae. Important concept: Man may act as both definitive host and as intermediate host for Taenia solium.

9.5.2.2.2 Identifiaction (See Figure 3.28)

The adult is 3 to 8 meters long and can live for up to 25 years. The scolex bears a rostellum with two rows of hooks. The uterus in the gravid prglottid has from 7 to 16 lateral branches. There are about 40,000 eggs in each gravid proglottid. The eggs are round and are 26 to 34 microns in diameter.

9.5.2.2.3 Life Cycle

The life cycle is similar to that T. saginata except the pig will serve as the intermediate host. The cysticercus is called Cysticercus cellulosae. The common name for the infected pork is measly pork. Cysticerci are found in the pig in the masseters, heart, tounge and shoulder muscles. Cysticerci may be found throughout the body.

Figure 3.28: Features of Taenia solium

Remember,

That man may serve as an intermediate host (and have cysticerci develop in his muscles) if he ingest eggs of T. solium. Cysticerci develop primarily in the subcutaneous tissue but other sites are the brain and ocular tissue (BAD NEWS). If the parasite develops in the ventricles of the brain, infection can cause pain, paralysis, epileptiform attacks and fatalities.

Clinical Signs, Diagnosis, Treatment and Control of Both T.Saginata and T. solium

 

9.5.2.2.4 Clinical signs

  • 1. In the definitive host, man - nonspecific abdominal symptoms: diarrhea, constipation, epigastric pain.
  • 2. In the intermediate host
    • a. Cattle and sheep infected with cysticerci are usually asymptomatic. Heavy experimental infections in cattle resulted in myositis, myocarditis, muscular stiffness and weakness. This occurs soon after infection and the animal recovers spontaneously.

      b. Man as intermediate host of T. solium - brain and ocular sites: pain, paralysis, epileptic seizures and DEATH.

9.5.2.2.5 . Diagnosis

  • 1. Definitive host (man) - identification of the eggs, scolex or proglottids.
  • 2. Intermediate host - postmortem examination (MEAT INSPECTION). T. saginata and T. solium are of public health significance. Infected carcasses will either be condemned or downgraded.

9.5.2.2.6 Treatment

1. Definitive Host (man)

  • a. Niclosamide at a dose rate of 2g. This drug may partially digest the scolex.
  • b. Paronomycin 5 mg/kg.
  • c. Quinicrine, 7-10 mg/kg.
  • d. Praziquantel, 10 mg/kg.

2. Intermediate host

  • a. Cattle and pigs: Albendazole, mebendazole, and praziquantel have been used experimentally to treat the larval stages in the musculature.
  • b. Man (T. solium): Removal of the offending cysticerci. The prognosis is not good.

9.5.2.2.7 Control

  • 1. Treat infected persons.
  • 2. Public education and hygiene.
  • 3. Proper meat inspection. This method is estimated to detect less than 50% of infected carcasses. Infected carcasses may be condemned for human consumption or treated by freezing at -100 C for 10 days to 2 weeks or by cooking at 50 to 600 C.

 

9.5.3 TAPEWORMS OF DOGS AND CATS

9.5.3.1 TAENIA OVIS

9.5.3.1.1 Host and Habitat

The adult tapeworm is found in the intestine of the dog. The intermediate hosts are sheep and goats. Mature cysticerci (Cysticercus ovis) develop in skeletal and cardiac musculature.

9.5.3.1.2 Identification

Adults are up to 1 or 2 cm long. The scolex has hooks; it is armed. The eggs are pva; amd 19 to 31 by 24 to 26 microns; they are typical taeniie-type eggs.

9.5.3.1.3 Life Cycle

Similar to T. saginata. Oncospheres are spread in the general circulation. Cysticerci develop in the skeletal and cardiac musculature (heart, diaphragm and masseters). Mature cysticerci are up to 6 mm long.

9.5.3.1.4 Pathogenesis and Clinical Signs

  • 1. Intermediate host (sheep and goats) - clinical signs are not usually seen in sheep and goats. The meat has an unaestheticappearance (measly mutton).
  • 2. Definitive host (dog) - To be discussed later.

9.5.3.1.5 Treatment, Diagnosis, and Control

To be discussed later.

9.5.3.2 TAENIA HYDATIGENA

The species name hydatigena has nothing to do with a hydatid cyst. This tapeworm forms a cysticercus.

9.5.3.2.1 Host and Habitat

The adult tapeworm is found in the small intestine of dogs, and wolves and other carnivores. Cysticerci (Cysticercus tenuicollis) are found in the intermediate hosts, domestic and wild ruminants, particularly sheep. Cysticerci are found attached to the greater omentum, intestinal mesentery and the serosal surface of organs.

9.5.3.2.2 Identification

Adult tapeworms are 75 to 500 cm long and have two rows of rostellar hooks. The eggs are oval and are 36 to 39 to 31 to 35 microns. Mature cysticerci are up to 6 cm long and contain a single scolex invaginated into a long neck. 

9.5.3.2.3 Life Cycle

Eggs are passed in the feces of the dog and are ingested by a sheep. The eggs hatch in the small intestine. The oncospheres reach the liver via the bloodstream. The larval tapeworm breaks out of the protal vessels and migrates in the liver parenchyma. They cause hemorrhagic tracts which may become fibrotic. The developing cysticerci migrate into the peritoneal cavity, mature and attach to the greater omentum, intestinal mesentery and the serosal surfaces of organs. They form large cysticerci (up to 6 cm) and contain a single scolex invaginated into a long neck. Carnivores become infected by ingesting the cysticerci.

9.5.3.2.4 Pathology

  • 1. Intermediate host (sheep) - the cysticerci migrate in the liver and cause hemorrhagic and fibrotic tracts. Viable, caseated or calcified cysticerci may be present in the liver. The liver will be condemned at slaughter.

    Heavy infection in young lambs will produce traumatic hepatitis and death. This condition must be differentiated from acute fascioliasis in lambs. It is easy to distinguish between an immature cysticercus and an immature fluke (F. hepatica) utilizing HISTOPATHOLOGY.

    The mature cysticerci in the peritoneal cavity ysyally cause no harm.

  • 2. Pathology of adult tapeworms in the dog - To be discussed later.

9.5.3.2.5 Diagnosis, Treatment, and Control

To be discussed later.

9.5.3.3 TAENIA PISIFORMIS

9.5.3.3.1 Host and Habitat

The adult tapeworm will be found in the intestine of the dog. The metacestode (larval stage) is a cysticercus (Cysticercus pisiformis) and is found in rabbits, hares and rodents.

9.5.3.3.2 Identification

The rostellum is armed. This tapeworm may grow to 200 cm. The eggs are slightly oval and are 43 to 53 by 43 to 49 microns. Typical taeniid-type eggs. The metacestode is found in the peritoneal cavity attached to the rabbit’s viscera. It is small cycticercus, about the size of a pea.

9.5.3.3.3 Life Cycle

Similar to that of T. hydatigena. The young stages develop in the liver of the rabbit. They penetrate the parenchyma of the rabbit and attach to the visceral organs in the peritoneal cavity.

9.5.3.3.4 Pathogenesis

  • 1. Intermediate host (rabbit) - in experimental infections, severe damage to the liver and death can result. Light infections may result in digestive disturbances and loss of condition.
  • 2. Definitive host (dog) - To be discussed later.

9.5.3.3.5 Diagnosis, Treatment and Control in Dogs

To be discussed later.

9.5.3.4 TAENIA TAENIAFORMIS - THE CAT TAPEWORM (ALSO KNOWN AS HYDATIGERA TAENIAFORMIS)

9.5.3.4.1 Host and Habitat

The adult tapeworm is found in the intestine of cats and other felines. This tapeworm has a strobilocercus as a larval form. A strobilocercus has a single scolex, which is not invaginated. The scolex is attached to its bladder by a long segmented strobila. The strobilocercus is found within the liver of rodents or rabbits, the intermediate hosts.

9.5.3.4.2 Identification

Adults are up to 60 cm long, lack a neck and have bell-shaped posterior proglottids. The eggs are 31-36 microns in diameter. They are typical taeniid type ova.

9.5.3.4.3 Life Cycle

Eggs are passed in the feces of the cat. A rodent ingests the egg and a metacestode (Cysticercus fasciolaris) develops in the liver. By 30 days after ingestion of the eggs, a "regulation" invaginated cysticercus develops. On day 42, however, the scolex evaginates and becomes connected to the bladder wall by a segmented strobila. It now resembles a small tapeworm connected to the bladder wall. This is called the strobilocercus. On ingestion of the rodent liver by a cat, the posterior portion of the strobila is digested and the scolex attaches to theintestinal wall and begins to form proglottids.

9.5.3.4.4 Pathogenesis

  • 1. Intermediate host (rat and rabbit) - NONE
  • 2. Definitive host - To be discussed later.

9.5.3.4.5 Diagnosis, Treatment and Control

To be discussed later.

IT IS NOW LATER!!!!!!

Pathogenesis of Taenia spp. in Dogs and Cats. Normally, infections with adults tapeworms are not very harmful to dogs and cats. Heavy infections in young animals may cause nonspecific abdominal signs: diarrhea, constipation or unthrifty pot-bellied appearance. The intestine may be obstructed (rare). Gravid proglottids may migrate out of the anal sphincter and be found in the perianal area or in the animal's bedding. Proglottids may be found on chairs, the floor or on the owner's clothes. The owner usually hates this. the dog may drag its anus over the ground. This clinical signs, however, may be associated with a pruritic anus or with impacted anal glands.

Diagnosis: Taenia spp. have "typical taeniid type eggs". This egg is difficult to find on fecal flotation unless a gravid proglottid has been ruptured during the process of defecation. Gravid proglottids may be found on the dog or in its environment; rupture them and examine for typical taeniid type eggs.

Treatment:

A wide variety of anthelmintics is available for treatment of Taenia spp. in dogs ans cats. Many should be preceded by an ovenight fast. Some of these effective anthelmintics are:

Control:

Dogs should not be fed raw offal or meat from slaughtered animals. Dogs and cats must be prevented from catching and eating small wild animals containing the larval forms of T. pisiformis and T. taeniaformis.

 

9.5.4 TAENIA TAPEWORMS OF THE GENUS MESOCESTOIDES

9.5.4.1 MULTICEPS MULTICEPS (ALSO KNOWN AS TAENIA MULTICEPS)

9.5.4.1.1 Host and Habitat

The adult tapeworm occurs in the small intestine of the dog and other canids. The metacestode (larval stage) is called a coenurus (sa-NUR-us) and is found in the brain and spinal cord of sheep and other ungulates (it is also recorded in man).

9.5.4.1.2 Identification

Adults are 40 to 100 cm in length. The scolex is armed. Eggs have a diameter of 29 to 37 microns. The larval stage, the coenurus, is a large fluid filled cyst, 5 cm or more in diameter. This cyst contains several hundred invaginated scolices along the cyst wall. This cyst is called Coenurus cerebralis.

9.5.4.1.3 Life Cycle

The egg is passed in the feces of the dog. It is ingested by sheep. The eggs hatch in the intestne. The oncosphere passes through the intestinal wall to the blood stream and is then carried throughout the body. If it reaches the CNS it develops into a coenurus, otherwise it dies. The developing larval stages in the nervous tissue migrate in the tissue leaving tortuous yellow-grey streaks. As the parasite matures, it develops to a coenurus. The coenurus is infective after 6 to 8 months. The dog becomes infected by ingesting the nervous tissue containing the coenurus.

9.5.4.1.4 Pathogenesis and Clinical Signs

The following are clinical signs in the sheep (the intermediate host). An acute meningoencephalitis may develop in lambs. More common is the development of one or two coenuri in the brain. Brain tissue is destroyed and the sheep will demonstrate neurological signs commonly referred to as "gid" or "staggers", or "sturdy". Most frequently the cyst is situated in the parietal region on the surface of one of the cerebral hemispheres. The animal holds its head to one side and turns in a circle towards the affected side. It may be blind in the eye on the opposite side. If the coenurus is in the cerebellum, the animal is hyperaesthetic and has a jerky or staggering gait. The animal may also be prostrate. If the coenurus is in the spinal cord, the animal exhibits pralysis of one or both hind limbs. The animal may exhibit these clinical signs intermittently. It will cease to feed, become emaciated and die. The parasite may localize on the surface of the brain and cause pressure atrophy of the skull.

9.5.4.1.5 Diagnosis

Diagnosis in the intermediate host is difficult. A specific serological test is not yet available. The adult tapeworm may be identified in the dog.

9.5.4.1.6 Treatment

Intermediate host: Treatment is useless in many cases. If the coenurus is located on the surface of the brain; surgical removal is possible. Albendazole has been used on occasion with beneficial results.

Definitive host: Many of the anthelmintics mentioned under Taenia spp. in dogs and cats are effective: e.g., Arecoline hydrobromide, Bunamidine hydrochloride, Praziquantel.

9.5.4.1.7 Control

Destroy the coenurus in carcasses. Do not allow the dog to ingest the coenurus. do not feed raw meat or offal from slaughtered animals to dogs.

9.5.4.2 MULTICEPS SERIALIS (ALSO KNOWN AS TAENIA SERIALIS)

9.5.4.2.1 Host and Habitat

The adult is a tapeworm found in the intestine of the dog and fox. The larval stage, a coenurus, develops in the subcutaneous and intramuscular connective tissues of rabbits. (It is called Coenurus serialis).

9.5.4.2.2 Identification

Multiceps serialis may grow to a length of 72 cm and possesses an armed scolex. The eggs are 31 to 34 by 29 to 39 microns. The coenurus may be 4 cm long. It contains numerous invaginated soclices arranged in rows.

9.5.4.2.3 Life Cycle

The egg is passed in the feces of the dog. It is ingested by a hare or rabbit. The larval stage, Coenurus serialis, develops in the intermuscular connective tissue. The dog ingests the raw flesh of the infected rabbit. Each invaginated scolex ingested develops into a tapeworm.

9.5.4.2.4 Pathogenesis and Clinical Signs

Not particularly pathogenic. The coenurus may interfere with muscle function.

9.5.4.2.5 Diagnosis

Identification of the ocenurus from the subcutaneous and intramuscular connective tissue of the intermediate host. Identification of the tapeworm in the dog.

9.5.4.2.6 Treatment

Same as that for Multiceps multiceps

9.5.4.2.7 Control

Do not feed raw rabbit viscera to dogs. Cook or freeze rabbit viscera before it is fed to dogs. Try to prevent dogs from catching and eating rabbits.

9.5.4.3 ECHINOCOCCUS GRANULOSUS(See figure 3.29)

9.5.4.3.1 Host and Habitat

The adult tapeworm is found within the small intestine of carnivores. The metacestode (hydatid cyst) is found in ungulates and man.

9.5.4.3.2 Identifiaction:

Adults are 2 to 7 mm long and usually possess 3 or 4 proglottids. The next to the last proglottid is mature. The terminal proglottid is gravid and takes up half the length of the worm. The rostellum is armed with two rows of hooks. The gravid proglottid usually disintegrates in the intestine so that eggs (not proglottids) will be found in the feces.

The eggs are typical taeniid eggs and are from 32 to 36 microns by 25 to 30 microns.

Figure 3.29: Features of Echinococcus Granulosus

C. Life Cycle

Eggs are passed in feces of the carnivore. They are immediately infective. They are ingested by either an ungulate (sheep, cattle or horses) or man. The oncosphere penetrates an intestinal venule or lymphatic lacteal, and migrates to the liver or lung. The hydatid cyst develops in the liver or lung. The size is usually 5 to 10 cm. Larger sizes occur in man (50 cm in diameter and containing 16 liters of fluid). The hydatid cyst produced is usually unilocular (it has only one compartment). The outer portion of the cyst wall is thick and laminated. The inner portion has a granular germinal membrae. From this germinal membrane develop the brood capsules. Brood capsules contain the developing prostoscolices. These brood capsules are infective for the definitive host. The following are variations which may take place within the hydatid cyst.

1. Variation 1:

The brood capsules may detach from the germinal epithelium float free in the cyst fluid.

2. Variation 2:

A daughter cyst (with its own germinal membrane) may develop within the mother cyst.

3. Variation 3:

If the original mother cyst wall is ruptured, protoscolices and brood capsules may develop into external daughter cysts.

4. Variation 4:

The original mother cyst may be sterile and produce no brood capsules or no daughter cysts.

The life cycle is completed when the dog ingests the protoscolices. These evaginate and penetrate deeply between the villi. In heavy infections the intestine becomes carpeted with worms.

 

9.5.4.4 ECHINOCOCCUS MULTILOCULARIS

9.5.4.4.1 Host and Habitat

Adult tapeworms occur primarily in foxes but also occur in dogs and cats. The hydatid cysts produced by these tapeworms are said to be alveolar - they are multivesicular infiltrative forms and are found in small rodents (field mice, voles, shrews, and ground squirrels). Man may serve as an intermediate host.

9.5.4.4.2 Identification

The adult tapeworms are 1.2 - 4.5 mm in length and they have an armed scolex. the hydatid cyst is alveolar - alveolar hydatidosis is serious, growth is peripheral and invasive. Like a malignant tumor, metastases can occur.

9.5.4.4.3 Life Cycle

Same as that of E. granulosus except that the definitive host is a fox and the intermediate host is a small rodent.

9.5.4.4.4 Pathogenesis

The adult tapeworm is comparatively harmless to the dog. In large numbers, you may see some enteritis.

Hydatid cysts of E. multiocularis are found primarily in the lungs where they are frequently multilocular. They are found in both te liver and the lungs of pigs, and also the livers of horses and cattle. In man the cysts are found in a wide variety of organs.

The pathogenicity of the hydtid cyst depends upon the severity of the infection and the organ in which it is located. In domestic animals clinical signs are not commonly seen despite heavy infections. Human hydatidosis is frequently associated with clinical signs particularly if the brain or the heart is involved.

Remember: E. multilocularis produces an invasive alveolar hydatid disease.

 

9.5.4.4.5 Diagnosis:

  • 1. In the definitive host: The eggs of Echinococcus spp. cannot be differentiated from those of Taenia sp. To confirm a diagnosis you must demonstrate the adult tapeworm. Use arecoline hydrobromide for purging and producing the adult.
  • 2. Hydatidosis in domestic animals is usually diagnosed during postmortem examination.
  • 3. Hydatidosis in humans may be diagnosed by immunoelectrophresis or by double diffusion tests. Radiographic diagnosis also is helpful.

9.5.4.4.6 Treatment of Echinococcus spp.

  • 1. Definitive host (dog, cat): The following compounds are effective against Echinococcus spp.
    • Arecoline hydrobromide
    • Arecoline acetarsol
    • Bunamidine hydrochloride
    • Nitroscanate
    • Praziquantel - the drug of choice
  • 2. Intermediate host: Hydatid cyst in man are usually treated surgically. The cyst fluid is aspirated and 2.5 to 10% formalin is injected. This kills the germinal membrane and the developing protoscolices. Do not spill cyst fluid - this will spread the cysts.

Mebendazole (available from the Centers for Disease Control) has been used to treat Echinococcus spp. in laboratory and domestic animals. Oral mebendazole has also been used in humans.

9.5.4.4.7 Control

Do not feed raw offal or meat from slaughtered animals. Prevent animals from cartching and eating small wild animals.

9.5.4.5 MESOCESTOIDES CORTI

9.5.4.5.1 Host and Habitat

This tapeworm occurs in the small intestine of the dog, cat, other carnivores, and man.

9.5.4.5.2 Identification

The worms are up to 250 cm long and 3 mm wide. The scolex has four suckers and no rostellum.

9.5.4.5.3 Life Cycle (See figures 3.30 and 3.31)

This is the only true tapeworm that has two intermediate hosts. The ova are found in the feces. Coprophagous oribatid mites ingest the eggs. Cysticercoids develop in these mites (the first intermediate host). When the first intermediate host is eaten by a second intermediate host (amphibia, reptiles, birds and mammals such as rodents, dogs and cats) a tetrathyridium is formed. A tetrathyridium is an elongate, solid bodied metacestode with a deeply invaginated acetabular scolex. They are 1 cm or more long and are found in the peritoneal cavity, the liver, and the lungs. Tetrathyridia will multiply asexually by longitudinal splitting of the parent scolex. Massive infections occur in the second intermediate host. When tetrathyridia are ingested by the definitive host they become adult in 16 to 20 days. However, it has also been shown that when tetrathyridia are ingested by dogs or skunks they reproduce asexually in the intestine. They may also reach the peritoneal cavity and multiply within it.

Figure 3.30: Life Cycle of Mesocestoides corit

Figure 3.30: Life Cycle of Mesocestoides corit

9.5.4.5.4 Pathogenesis

Intestinal infections with Mesocestoides in the dogs are usually harmless. Sever diarrhea can occur in human intestinal infections. Infections with tetrathyridia in dogs and cats can cuase a severe parasitic peritonitis and ascites.

9.5.4.5.5 Diagnosis: Identification

9.5.4.5.6 Treatment

Praziquantel is the drug of choice.

9.5.4.5.7 Control

Prevent dogs from ingesting the small wild animals (rats, mice, and rabbits). This control is difficult due to the wide range of intermediate hosts.

9.5.5 CLASS COTYLODS OR PSEUDOTAPEWORMS

9.5.5.1 GENERAL INFORMATION

A. The two pseudotapeworms are:

B. Members of this class all have the following characteristics: (see figure 3.32)

Figure 3.32: Feature of Pseudotapeworms

9.5.5.2 DIPHYLLOBOTHRIUM LATUM, THE BROAD FISH TAPEWORM

9.5.5.2.1 Host and Habitat

The adult tapeworm is found in the small intestine of man, dog, cat, pig, polar bear, and other fish eating mammals in many parts of the World. (Northern Europe and the Great Lakes Area are loclites where this tapeworm is found).

9.5.5.2.2 Idnetification

The adult tapeworm may attain a length of 30 feet. It is yellow grey in color and has dark central markings caused by the uterus and eggs. The gravid proglottids have this Rosette Effect. Proglottids are usually wider than they are long. Eggs are passed continuously in the feces. They are light brown, operculate, 67 to 71 microns by 40 to 51 microns and have rounded ends.

9.5.5.2.3 Life Cycl (see figures 3.33 and 3.34).

The operculated egg is passed in the feces. It must be passed into water for development to occur. This takes from 8 days to several weeks depending on the temperature. A coracidium is produced within the egg. The coracidium is a six hooked oncosphere covered with a ciliated embryophore. The coracidium emerges from the egg and swims in the water. A predaceous copepod eats the coracidium and a procercoid develops in the body cavity of the copepod. The procercoid is the first larval stage and is found in the first intermediate host, a copepod. Infection of the second intermediate host, fresh water fish (pike, wall-eye, perch, trout), is by ingestion of the infected copepod. When the infected copepod is eaten by a fish, the procercoid is released in the fish's intestine. The procercoid bores its way through the intestinal wall and into the body muscles. in the muscles it develops into a plerocercoid. The plerocercoid may show evidence of bothria on its anterior end. Plerocercoids are encysted and coiled in the musculature, although they may be in the viscera of the fish. They appear as white masses in uncooked fish. When the plerocercoid is ingested by a suitable host, the muscle of the fish is digested, but the plerocercoids are not. They attach to the small intestine and begin to grow. By 7 to 14 days, the tapeworms are producing eggs.

Man is infected by eating raw or slightly pickled fish. Dogs are infected by eating raw fish offal.

9.5.5.2.4 Pathogenesis and Clinical Signs

Many cases of diphyllobothriasis are asymptomatic. Affected individuals will pass long chains of spent proglottids. Many exhibit poorly defined symptoms: vague abdominal discomfort, diarrhea, nausea, and weakness. Many individuals infected with D. latum will exhibit a pernicius anemia (a macrocytic, hypochromic anemia). D. latum absorbs a large amount of vitamin B12 and interferes with the patient's ability to absorb vitamin B12.

Figure 3.33: Life Cycle of Diphyllobothrium latum

Figure 3.33: Life Cycle of Diphyllobothrium latum

9.5.5.2.5 Diagnosis

Demonstration of the spent proglottids or chartacteristic operculated eggs passed in the stool gives a positive diagnosis.

9.5.5.2.6 Treatment

Praziquantel, niclosamide, and quinacrine are drugs of choice.

9.5.5.2.7 Control

Freeze or cook fish properly. Do not feed raw fish offal to dogs. Make sure communities do not empty raw sewage into freshwater lakes.

9.5.5.3 SPIROMETRA MANSONOIDES - THE "ZIPPER" TAPEWORM

9.5.5.3.1 Host and Habitat

This tapeworm is found in the jejunum of dogs, cats, and racoons.

9.5.5.3.2 Identification

These are small to medium size tapeworms and they closely resemble Diphyllobothrium. The uterus is spiraled (and not rosette form) in the gravid proglottid. The eggs are pointed, rather than rounded.

9.5.5.3.3 Life Cycle (See figure 3.35)

Eggs are passed continuously in the feces and develop to produce a coracidium. The coracidium is swallowed by a fresh water Cyclops. The mature procercoid is reached in 10 to 14 days. Plerocercoids or spargana occur in the second intermediate hosts. These may be water snakes, tadpoles, other amphibia, alligators, birds and mammals, including man. The plerocercoids are white ribbon-like structures that may reach several centimeters in length. Cats and dogs ingest the second intermediate host. Cats, dogs and raccons may be infected with both plerocercoids an adult tapeworms. Plerocercoids in the tissues of cats and dogs can migrate to the gut lumen to continue development.

9.5.5.3.4 Pathogenesis and Clinical Signs

This tapeworm is of public health significance. Man may become infected by:

  • 1. Ingesting crustaceans infected with procercoids. Procercoids migrate to subcutaenous tissues and develop to plerocercoids.
  • 2. By the ingestion of plerocercoids in the second intermediate host. Humans are unsuitable definitve hosts - the plerocercoids migrate into the tissues and reestablish as plerocercoids in the subcutaneous tissues of man.
  • 3. By the application of a poltice - when infected frog or snake flesh is used ot dress wounds on eyes, the pleroceroids may migrate into the flesh of the eye.

Spargana is man migrate in the subcutaneous tissue, muscle and the periorbital area. There is inflammation, urticaria, edema, and eosinophilia.

9.5.5.3.5 Treatment

Treatment of humans is by surgical removal of spargana. Dogs and cats - praziquantel.

9.5.5.3.6. Control

Control is diffucult due to the wide range of intermediate hosts.

 Figure 3.35: Life cycle of Spirongtro Mansondoides

 

Table 9.1 The Cestodes of Tapeworms