Chapter 17 ZOONOSES & PRINCIPLES OF HEALTH MAINTENANCE  DR. JAMES A. FERGUSON AND DR. D. T. CAPPUCCI, JR

 

 

17.1 Objective:

To review some of the zoonoses and principles of animal and public health maintenance.

17.2 Introduction

Definition: zoonosis (plural, zoonoses)- disease common to animals and humans.

Pertinent aspects of zoonotic diseases:

• - Etiologic agent
• - Disease in humans and animals
• - Transmission
• - Epidemiology, significance
• - Control, prevention

17.3 General

Zoonoses relatively uncommon now in the United States because of vaccines, eradication programs, vector control, improved sanitation, other factors. They are still quite important in underdeveloped and some developing countries and in areas of the U.S. where prevention and control may be inadequate (e.g., Indian reservations).

Large number of diseases in this category - some on list quite rare. There are many tropical diseases. Note that some are transmissible from animals to man or vice versa, while others are merely common to both.

17.4 Specific Disease Entities

17.4.1 Bacterial

Infection usually from ingestion, inhalation, direct contact; occasionally via vectors. Usually treatable (antibiotics), often preventable (vaccines).

• - Five species of organism from multiple animals (primarily swine, cattle).
• - Disease in humans - undulant fever; flu-like illness. May last few days or recur over several years. Rarely fatal.
• - Disease in animals - abortion, reproductive tract inflammation. May be asymptomatic shedding in milk or in vaginal discharges.
• - Transmission - ingestion, direct contact with infective material.
• - Epidemiology - incidence down considerably over last 17 years. (246 cases in 1974 compared to 89 cases in 1991). Primarily an occupational disease, thus mostly males affected. Most probable source - swine (B. suis). B-canis from dogs - first isolated 1966, with approximately 20 or more cases on record.
• - Control - testing (milk, serology), slaughter, vaccination man and animals), occupational precautions.

18 serogroups, many serotypes - approximately 175 serotypes (approximately 24 presently in test battery).

• - Humans - fever, headaches, nausea, muscle aches, jaundice, anemia. 5% of cases die. Some asymptomatic cases.
• - Animals - cattle, swine, dogs most important. Signs - abortion, milk production, jaundice, G. I. and renal involvement. May be symptomatic or may have post clinical shedding of organisms in urine, placental discharges for 6 months +. Rats major reservoir.
• - Transmission - ingestion, skin penetration, vehicles, vectors, droplets.
• - Epidemiology - 119 cases in 1975 compared to 59 cases in 1991. Decreasing incidence in recent years. Higher in summer - many recreational exposures, some occupational (more males than females). Worldwide incidence.
• - Control - treatable disease, vaccines, education.

• - Causative agent Chlamydia psittaci (Bedsonia group). Reportable disease. Intracellular parasite.
• - Humans - many subclinical cases, others with mild flu-like symptoms. May progress to pneumonia. More severe in persons over 50. Occasionally fatal. Treatable.
• - Animals - birds primary reservoir. Birds often asymptomatic but large kills may occur. Various strains (undetermined number) differ in virulence for humans, birds, animals. Animal disease variable (arthritis, abortion, pneumonitis). Birds exhibit diarrhea, wasting, conjunctivitis. Occasional isolates from livestock and other animals have occasionally been implicated in the cause of disease in humans.
• - Transmission - usually aerosol. Organism excreted in bird feces, stable when dried. Aborting animals present additional risk for transmission.
• - Epidemiology - generally 40-60 or more cases per year. A total of 163 cases occurred in 1974, and 117 of these were associated with 7 outbreaks in turkey processing plants. In 1991, there were 87 cases in humans. Parrots a most likely source, then pigeons and parakeets. Eye infections and abortions have occurred in humans who have had contact with infected aborting sheep.
• - Control - difficult. 30-day quarantine, treatment of imported birds. Routine serologic testing of turkey flocks, treatment when indicated. No vaccine.

17.4.2 Mycotic

Not reportable so epidemiology not well established. Many ubiquitous, often secondary to other diseases. Not usually contagious.

• - Humans - usually acute respiratory disease (may mimic TB). May be disseminated in lungs, bone marrow, other organs. May progress over months or years.
• - Animals - most confirmed cases in dogs, some in cats, livestock, wildlife (few animal cases confirmed).
• - Transmission - inhalation of spore from environment. Occasionally vehicles (e.g., feathers).
• - Epidemiology - is natural soil contaminant. Humans, animals accidental hosts. Major sources - old chicken houses,starling, pigeon roosts, bat caves. Endemic in many areas - note positive skin reactors. Unapparent cases common.
• - Control - soil decontamination, bird control, environmental cleanup.

• A fungal disease of keratinized tissues. Two major genera: Microsporum spp. and Trichophyton spp. Various species tend to have host preference.
• - Humans - hair loss, sterile lesions, itching - head, groin, feet, nails.
• - Animals - hair, nails. More common in cats, cattle, less in dogs, other species, including birds.
• - Transmission - direct, indirect contact with infective debris, including fomites, and possibly arthropods. Organisms may survive months, years.
• - Epidemiology - large number of unapparent carriers, worldwide. Lesions often not obvious on animals. Stress can lead to clinical disease.
• - Control - treatable disease. Since environment is a constant source of organisms, educate relative to precautions and hygiene.

17.4.3 Parasitic

17.4.3.1 Protozoan

One-celled, intracellular. Mainly a tropical disease or common in underdeveloped countries. Often involves vector transmission.

• - Involvement of multiple tissues. Rare disease but common infection due to Toxoplasma gondii and other species.
• - Humans - asymptomatic or flu-like illness, pneumonia, encephalitis, abortion retardation, retinitis.
• - Animals - abortion (cattle, sheep), respiratory, G.I. asymptomatic.
• - Transmission - congenital, ingestion (cysts or oocysts). Of primary concern to pregnant women. Possibly vectors.

NOTE: role of cats.

• - Epidemiology - 27-40% antibody positive. Usual sources cat feces, uncooked meat. Reported worldwide.
• - Control - treatable (variable effectiveness). Education, vector control.

17.4.3.2 Cestodes (tapeworms)

• Require intermediate host

Three (3) segmented tapeworm. Definitive host dogs, possibly wild carnivores. Intermediate host-man, livestock (mainly sheep, swine, cattle). Three common species: Echinococcus granulosus, E. vogeli, and E. multilocularis.

• - Humans - cysts in lung, liver, brain, bone marrow. Rupture can be fatal. Treatment - surgery.
• - Animals - usually lung, liver, cysts.
• - Transmission - ingestion of eggs from dog feces. Possibly via vectors.
• - Epidemiology - prevalence unknown. Endemic in California, Utah, Idaho. Recent episode in Southeast involved infected foxes/E. multilocularis transported from the Mid-West for fox hunting.
• - Control - eliminate dog infestations and exposure to livestock viscera.

17.4.3.3 Nematodes (roundworms)

• Human disease caused by migration of larvae (Trinchinella spiralis and other species).
• - Humans - most infections subclinical. Signs - fluid swelling of face, muscle pain, fever, diarrhea, eye pain.
• - Animals - parasite probably adaptable to all animals, some birds. Widest host distribution of any helminth. Swine main source for humans
• - signs of illness in swine similar to disease in people.
• - Transmission - same animal intermediate and final host. Domestic cycle involving pork scraps and wildlife. (Predatory cycle)
• - Epidemiology - of continuous importance, with resurgence in 1974 (141 cases) and in 1975 (220 cases). In 1991 there was a marked decline (61 cases). In swine, the disease is decreasing. However, pork sausage is the source of more than 85% of cases in humans.
• - Control - feeding of swine other than uncooked garbage. Education of public regarding the cooking of pork, freezing, curing. Rodent reduction. Disease is treatable.

   

      

         
Example
         2. Visceral Larva Migrans
         
      
   

• - Cat and dog roundworm larvae (Toxocara spp.) easily infect humans.
• - Humans - fever, weight and appetite loss; muscle, joint, abdominal pain; retinal scars.
• - Animals - adults in intestinal tract - domestic, wild canine and feline.
• - Transmission - ingestion. Can be prenatal infection in animals. Also ingestion of rodents. Immunity in adult dog.
• - Epidemiology - worldwide. Primarily in children 1-3 years. No accurate data.
• - Control - education, animal treatment.

17.4.3.4 Trematodes (flukes)

• - Humans share several fluke infections with other animals (schistosomiasis, lung fluke disease and so forth. Some of these infections may be acquired by eating raw or undercooked fish, shellfish, or contaminated vegetables. Others may be acquired by dermal contact with water containing infective cercariae (stage in the life-cycle of flukes).
• - Animals - flukes are a major concern in cattle production in and around swampy areas and wetlands.
• - Epidemiology - worldwide, especially in the tropics and sub-tropics.
• - Control - education, animal treatment, snail control, pasture and land management.

17.4.4Rickettsial

• - between virus and bacteria in size. Mainly intracellular pathogens, and usually vectorborne.

• - Humans - headache, chills, muscle aches, nausea, fever leading to rash. 20% mortality if untreated. Diagnostic problem, but readily treated.
• - Animals - reservoirs - wildlife (principally rodents), Many species including birds show antibodies. Dogs also show titers, but rarely clinical signs. Importance as reservoir unknown although important source of infected ticks. Bird migration can spread ticks over vast distances.
• - Transmission - Two (2) tick species in U.S. are common vectors. Must be attached 10-20 hours for successful infection.
• - Epidemiology - increasing in importance since 1963. 850 cases in 1975; 635 cases in 1991. Tends to be seasonal (summer), in eastern half of U.S. Recreational, rural exposure.
• - Control - education, tick control on dogs and premises, physician education. Vaccine of questionable value.

17.4.5 Viral Diseases

• 1. Arthropod-borne - only mosquito-borne encephalitides of importance in U. S.-grouped into three categories:

Examples 

Group A:

• - Eastern Equine Encephalomyelitis (EEE)
• - Western Equine Encephalomyelitis (WEE)
• - Venezuelan Equine Encephalitis (VEE)

Group B:

• - Saint Louis Encephalitis
• - Group C:
• - California Sero Group-California Encephalitis

The above varies as to severity in man, animals, geographic area of involvement. All include animal and/or avian reservoir as source of virus.

• - Eastern equine - most severe (up to 60%) mortality - man, over 90% horses). four (4) cases - 1974 with same number of cases (4) in 1990. Historically tens to occur along coastal U.S. from New England to southern tip of Texas. Avian reservoir.
• - Western equine - similar clinically to EEE, although case fatality only 5-15%. Two (2) cases - 1974 with zero (0) cases in 1990. Historically occurs in western two-thirds of U.S. A. Avian reservoir (starlings, sparrows, and other birds).
• - Venezuelan equine - uncommon human disease in U. S. - generally mild. High mortality in horses. Generally confined to southern, southwest border areas. Equine vaccine widely used. Rodent and possibly avian reservoirs.
• - Saint Louis encephalitis (SLE)
• - Humans - fever, headache, stiff neck, nausea, central nervous system abnormalities. Case fatality % (25% + in older age groups).
• - Animals - wild birds only important reservoir. Asymptomatic.
• - Transmission - primarily Culex mosquitoes. Bird-mosquito-bird cycle with human as dead-end host. Disease of late summer, fall.
• - Epidemiology - SLE comprises over 70% of arboviral encephalitis since 1955 in U.S. Primarily a clinical disease of older people, although all age groups probably equal risk of infection. More likely in lower socioeconomic groups. Approximately 150 cases in 1990.
• - Control - reduction of mosquito breeding, mosquito control, public education to reduce exposure.
• - California encephalitis - similar clinically to others. Geographically scattered foci of infection. Rodent reservoir. Approximately 25 cases in 1990.

17.4.5 Viral Diseases - nonarthropod-borne

• - Humans - invariable fatal. Behavior change, headache, fever,pain at site of bite, death in 2-6 days.
• - Animals - similar signs, although indications that some species can secrete virus in saliva without developing clinical illness. Other species can survive variable periods (weeks), although dogs, cats die within 10 days once salivary secretion begins.
• - Transmission - bite, aerosol
• - Epidemiology - generally 1-3 human cases per year. (Three human cases in 1991). 2,677 animal cases in 1975, 85% of which were in wild animals. In 1991, there were 6,486 cumulative cases (preliminary data) of animal rabies, largely in wildlife. Skunks result in 50% of wildlife cases. Other important feral species - foxes, bats, raccoons. Prevalence of various species may vary geographically.
• - Prevention and Control - vaccination of domestic animals, animal control, possibly wildlife vaccination. Preexposure immunization of humans. Adjunct procedures such as licensure of dogs/cats, leash laws, and quarantine and travel restrictions/international-interstate import compliance.
• - Postexposure Management - Any animal bitten or scratched by a wild, carnivorous mammal (or a bat) not available for testing should be regarded as having been exposed to rabies.

17.5 Principles of Animal and Public Health Maintenance

Paul R. Schnurrenberger (deceased) : Prepared by a Faculty Committee of the School of Veterinary Medicine, Auburn University

• 1. Maintaining animal health, a positive concept, results in more efficient production than does the mere prevention of disease.
• 2. A health maintenance program should be considered as a dynamic, coordinated entity, not as a patchwork of unrelated, unchanging procedures. Every aspect of the health program must be flexible so it can be adjusted to changing situations.
• 3. Maintenance of health requires the expertise of many disciplines and occupations but the veterinarian is the person best qualified to determine when advice from another specialist is needed.
• 4. The law of limiting factors is just as applicable in health maintenance and animal production as in any other ecological situation.
• 5. Changing the limiting factor may increase the carrying capacity but this increased stress on the ecosystem may produce other hazards.
• 6. Many disease hazards are reduced most effectively and efficiently through altering the environment or management practices. Each contemplated environmental or management change should be evaluated in terms of its effect on health maintenance.
• 7. The air, soil, and water should be free of physical, biological and chemical health detractors.
• 8. Preventing exposure to the etiologic agent is the surest way of preventing disease.
• 9. One of the bases of any health maintenance program is an adequate nutritional program, including an ample supply of suitable water.
• 10. Infectious and noxious agents need not always be excluded from an area. It may be sufficient, or even desirable, to provide barriers which reduce the exposing dose of these agents to a subinfective or subclinical level.
• 11. Direct transmission of infectious agents is in proportion to the frequency and extent of contact between animals.
• 12. Disease transmission may be minimized by segregating animals according to species and age.
• 13. Small, stable populations discourage transmission of disease.
• 14. No animal or item should be placed in contact with the herd until it is certain that it is free of health detractors.
• 15. When feasible, diseases should be eradicated and measures instituted to prevent their being reintroduced. When this is not feasible, controls should be instituted.
• 16. Potential disease producing situations vary be disease, time and place. Each should be evaluated and solved according to its own characteristics.
• 17. A problem in curative medicine has not been solved until the health maintenance program has been adjusted to eliminate or reduce the probability of its recurrence.
• 18. Livestock production will not be profitable unless the location selected is suitable for the operation in question, and will remain so for an economically justifiable time.
• 19. Adequate shelter and enclosure provide protection from the elements, parasites, and predators, and keep animals in desired areas. This is accomplished with adequate space, light, ventilation and sanitation. Attention is given to physical, social and psychological needs of the animals.
• 20. Sanitation consists of prompt, proper removal and disposal of solid, liquid, and gaseous wastes in order to maintain a healthy environment.
• 21. All production personnel (owners, managers and other workers) and specialized consultants must understand and meet their commitments if a health maintenance program is to function properly.
• 22. Division of responsibility should be accomplished so as to achieve the optimal balance between economy and expertise. Each task should be performed by the person who is competent to perform it at the lowest cost under routine conditions, but who can recognize when a situation is not routine. At that point, the task is referred up the cost-competency ladder until the necessary level is reached.
• 23. One of the most frequent causes of breakdowns in a health maintenance program is faulty communication. Instructions should be given clearly and completely, then repeated by the recipient as a check on accuracy.
• 24. Animals should be observed with sufficient regularity and detail to detect abnormalities in an individual or group at the earliest possible moment. The timing and scrutiny are determined by the risk and severity of anticipated abnormalities.
• 25. An early accurate diagnosis is a major step toward prevention and control.
• 26. Increased knowledge of the causes and epidemiology of a disease improves the likelihood that prevention can be achieved but complete knowledge is not always necessary.
• 27. Preventive measures should begin with those diseases which the animal has the greatest risk of contracting.
• 28. Cost-effectiveness is always a consideration in production of food and fiber animals. As a result, the optimal situation must often be tempered to one which is nearly adequate.
• 29. Cost-benefit ratios must include psychological factors for the animal, producer, neighbor, consumer, and society in general.
• 30. Cost-effectiveness studies should be of a long range nature since increased production persists for the duration of the improvement in health status.
• 31. Every health maintenance procedure must be evaluated for its economic feasibility before it can be instituted.
• 32. Records should contain sufficient details on all aspects of the operation to permit adequate epidemiologic and cost: benefit analyses.
• 33. The most economical way to increase herd size is through efficient reproduction of high quality foundation stock.
• 34. Breeding programs should include disease resistance as an indirect means of genetic improvement of production.
• 34. Judicious culling is an important means of improving herd quality and health.
• 36. Permanent identification of production units is essential for good management. The unit may be an individual or a group depending on the species and type of operation.
• 37. All decisions should be based on the most accurate, current knowledge in existence.