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Certain Gram-negative bacteria play a significant role in contributing to losses suffered by the animal industry due to infection. For example the genus Pasteurella is part of a multiple complex disease of bovine called pasteurellosis "shipping fever complex" hemorrhagic stockyard disease, etc. This infection is largely due to the shipment of cattle to long distant markets by railroad or by trucks. It appears that added stress on the animals brought about by inadequate rest stops and contaminated water and feed increases the susceptibility of these animals to the Pasteurella which may be normally present on the mucus membrane.
The Pasteurella is responsible for respiratory infection in other animal species such as swine, sheep and goats, rabbits and other rodents. The predominant species P. hemolytica and P. multocida can readily be identified by their characteristics coccoid, short, blunt rods shape and the ability to demonstrate........ staining.
The genus Hemophilus is the example of a Gram-negative organism of which many are not significant as inciters of disease. However, there are certain species that are important as disease entirely for animals. Hemophilus is important in swine influenza or hog flue. The organism works in concert with influenza virus to produce the disease which neither can produce alone.
Hemophilus somnus (agri), the cause of infectious meningo-encephalitis in cattle has become an important disease in North America. The organism colonizes in the respiratory tract after natural exposure and is transmitted horizontally to other animals.
Most Hemophilus species require the X and V-factor, but H. somnus does not respond to them but requires an unknown factor in blood and yeast. It inhibits satellitism when grown near a feeder culture.
Malleomyces mallei (Glanders) is an infectious disease primarily of horses. This disease has been eliminated or controlled in most well-developed countries but remains quite prevalent in some of the developing countries. The infection is contracted in most instances through ingestion although it probably can occur through inhalation and wound infection. Historically, from ancient to modern times, wars have always caused the disease to flourish and the distribution of army animals to civilian service has served to spread the disease. The respiratory tract is the target organ in the acute form of the disease resulting in a fulminating pneumonia which is seen mainly in mules. A more insidious form coupled with purulent pneumonia is seen in horses. The disease may be diagnosed by demonstrating compliment fixation antibody or a positive reaction to mallein. The mallein test is based on a delayed type hypersensitivity.
Infectious bovine keratoconjunctivitis (IBK) is caused by Moraxella bouis. The disease occurs in cattle only. The disease is most common in summer and autumn and reaches epizootic proportions when flies and dust are abundant and the grass is long. Transmission is thought to be by means of these reagents contaminated by ocular discharge of infected animal. The conjunctiva is the most probable port of entry. Lesions of IBK are localized in the eye; the organism does not reach the blood stream of the infected animal serum agglutination and precipitiniogenes are detectable.
Two other closely related organisms causing infection in cattle that will be discussed in chapter 11 are actinobacillosis the causative agent of wooden tongue and actinomyces bovis the primary etiology of lymph jar.
Actinobacillus lignieresi is the only species causing wood tongue which is characterized by inflammation of the rod shaped organism is encased in small cheese like granules in the exudates and are quite similar to the sulfur granules of actinomycosis, but are generally smaller.
In culture it coccobacillary, occurring singly impairs or short chains. However pleomorphic coccal, long rod, or filamentous forms can occur. The organism is Gram-negative. The pathogenicity for man is not significant.
Actinomyces bovis is the primary cause of lumpy jar which commonly occurs only in cattle occasionally a case may occur in swine. In lesions the organism stains Gram-positive and may appear as cocci, rods of varying size, filament, branching form or club shaped. In cultures the A. bovis grows as a long filamentous branching organism.
Much attention has recently been given to infectious atrophic rhinitis a disease of swine characterized by atrophy of the nasal turbinates. Two organism have been incriminated as the causative agents of the disease which are Brodetella bronchiseptica and Pasteurella multocida type D. However, B. bronchiseptica appears to initiate the infection. Atrophic rhinitis is of considerable economic importance in the swine industry since 25-40% of all hogs slaughtered in the United States are affected with the disease. The disease causes a serious depression of growth rate and added time to produce market weight hogs. Transmission of the disease is by way of infective aerosols. Attempts to control the disease has been through the use of antibiotic and vaccination programs and strict management practices.
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Pasteurellosis bovis, shipping fever, hemorrhagic septicemia, hemorrhagic stockyard disease, stockyard pneumonia, enzootic pneumonia of calves, swine plague.27.3.2 Definition:
Pasteurellosis is an acute infectious disease of cattle, sheep, swine and rabbits caused by Pasteurella multocida and P. hemolytica and characterized by hemorrhagic septicemia and pneumonia. The infection is most often seen in young animals.
27.3.3 General Characteristics:
Pasteurella are coccoid, short, blunt rods, usually demonstrating bipolar staining. They are Gram negative. The majority are capsulated, nonmotile and nonsporeforming. Pasteurella colonies are medium sized, gray opaque, and do not demonstrate the biconvex appearance as do those of the enteric group. The Pasteurella have a characteristic odor, sometimes described as sour, and sometimes referred to as being similar to that of unscented toilet soap.
In this discussion, emphasis will be placed on the two main species of concern in veterinary medicine--Pasteurella hemolytica and P. multocida.
Pasteurella hemolytica will usually demonstrate hemolysis on blood agar;P. multocida will not. This hemolytic pattern is variable and usually confined to an area restricted under the colony as opposed to a wide zone of hemolysis seen in organisms such as Streptococcus and Listeria. The Pasteurella will not grow on EMB or SS agar, thus differentiating them from the enteric Gram negative rods. They will produce small pink colonies on McConkey's agar; this pink color indicates lactose fermentation. Pasteurella multocida will not grow on McConkey's agar. Pasteurella multocida characteristically give a positive indole test while P. hemolytica ferments sugar with the formation of acid but not gas. Acid formation is not as pronounced as is seen with enteric organisms.
Summary of Cultural Features of the Main Species of Pasteurella
__________________________________________________________
Species hemolysis EMB McConkey's Indole Dextrose Lac Suc Malt
P. hemolytica + no growth growth - A A A A
P. multocida - no growth no growth + A - A -
__________________________________________________________
A = Acid
27.3.4 Historical Facts:
- a. First significant report by Bollinger in 1878 following investigation of fatal disease among wild animals and cattle.
- b. In the U.S., Salmon and Smith described the organism in 1880.
- c. Loeffler and Schutz observed and described the organism of swine septicemia in 1882.
- d. In 1885, Kitt made a comparative study of the organism producing fowl cholera, swine septicemia and the septicemia of rabbits, wild animals and cattle. He concluded that the organism recovered from each was in many respects the same and referred to them as Bacterium bi-polare multicadium.
- e. When the Pasteurella genus became established the species name was based on the nomenclature described by Flugge, hence the organism was renamed Pasteurella oviseptica.
- f. Further research on strains isolated from the different animals has failed to support a zoological classification. All of the strains are morphologically, biochemically, serologically and pathologically similar.
27.3.5 Occurrence and Distribution
Pasteurella multocida is encountered throughout the world and is frequently the cause of great economic loss. Pasteurella hemolytica has been reported in the United States, Sweden, Norway, England and Japan.
27.3.6 Etiology
Nomenclature of the disease caused by infections with Pasteurella spp. in farm animals has been confusing. Based on clinical signs and on the bacteria commonly associated with each entity a suggestive nomenclature is set forth:
Septicemia Pasteurellosis of Cattle (aka, hemorrhagic septicemia) is commonly associated with P. multocida type I or B, and is the classical disease of Southern Asia characterized by a peracute septicemia and a high mortality rate.
Pneumonia Pasteurellosis of Cattle is commonly associated with infection by P. multocida type II or A and P. hemolytica, is common in the western hemisphere and Europe. It is characterized by a bronchopneumonia, a long course and a lower mortality than in the case of septicemic pasteurellosis.
Pasteurellosis of swine, sheep and goat P. multocida: is usually seen as the pneumonic form in swine. Pasteurellosis of sheep and goats is usually due to P. hemolytica in the pneumonic form, although a septicemia form is also seen, especially in lambs.
27.3.7 Resistance
Laboratory cultures of Pasteurella die out quickly, and transfers must be made at least twice each month. Organisms dried on cover glasses in the air and protected from light usually die in less than 24 hours. Cultures are quickly and easily killed with all ordinary disinfectants. Many organisms of the Pasteurella genus have been isolated from the normal mucus membranes but it is doubtful if they thrive elsewhere.
27.3.8 Transmission
Transmission is by contact and the consumption of contaminated food and water. In some cases droplet infection is of significance since the infectious agents may be coughed up or exhaled by infected animals which maybe clinical or recovered cases in which the infection persists in the upper respiratory tract. The organism may be a normal inhabitant of the respiratory tract.
27.3.9 Clinical Picture
Cattle, goat and sheep:
Hemorrhagic septicemia of these animals usually takes the pectoral or pneumonic form. The affected animals suffer from a very high fever (1060F to 1080F or higher). They breathe with great difficulty in the later stages of infection, and the death rate is high. In cattle, the disease often occurs after exposure or shipping fever or shipping pneumonia. It is thought that the extreme fatigue suffered by the animal while kept in crowded quarters for many hours in transit between irregular feeding and watering stops increases susceptibility to the disease. It is not clear whether all cases known under the names are pasteurellosis, since there are reports of instances in which Pasteurella organisms were not found and evidence to suggest that a virus was concerned. An accumulation of evidence indicates that a myxovirus belonging to the parainfluenza group (PI3) may be associated with shipping fever.
Swine:
The clinical signs of pasteurellosis of swine are those of broncho-pneumonia. Signs vary, depending upon severity and lung involvement. In cases of mild pulmonary pasteurellosis, the only clinical sign may be coughing. The bronchopneumonia in which severe and labored abdominal breathing (thumpy or thumping) is common an known as a secondary breakdown. In a severe case of the disease, the body temperature is 1050F to 1060F. A muco-purulent nasal discharge is frequently present. Anorexia, general weakness along with depression and frequent prostration are evident in the acute disease. The clinical course in the case of acute disease ranges from 5 to 10 days with a usually fatal termination in the absence of effective treatment.
27.3.10 Pathogenesis
Cattle, sheep and goats:
Hemorrhagic septicemia is marked by hemorrhages on serous surfaces, blood-stained fluid in the thorax and abdomen, enteritis and edema in the subcutaneous tissues (in the less acute forms). The bronchopneumonia seen with shipping fever shows moderate amounts of fibrin on the lung surface, areas of pneumonia and greatly thickened septa. On the otherhand, the pneumonia produced by P. hemolytica produced much greater amounts of fibrin, and thus is a true fibrinous pleuropneumonia.
Swine:
Swine plaque usually takes the form of a fibrinous pneumonia accompanied in some cases by septicemia. The pathology of the lungs frequently involves the anterior lobes of the lung and anterior portion of the diaphragmmatic lobes as well. The lungs are firm and liverlike in consistency. The surface of the lung is covered with a serofibrinous exudate, and a turbid fluid containing flakes of fibrin is found in the thoracic cavity. The cut surface of the involved lung is firm and mottled in color.
27.3.11 Laboratory Diagnosis
The bipolar organism can be demonstrated in abundance in stained films made from the pneumonic tissue of swine. They may be readily cultivated from these tissues and are often found in large numbers in stained sections in the exudate in the alveoli. In such cases the organism shows very little virulence for rabbits. This is not true of Pasteurella organism found in other animals. It appears doubtful that these organisms are the primary cause of the disease; however, it is quite probable that they play a major role in the production of the pneumonia that is the immediate cause of death.
A few organisms can often be recovered from the spleen and blood of cattle suffering from Pasteurella pneumonia. However, they are not usually found in large numbers, and the disease is not regarded as a bacteremia. In addition, hemorrhages have never been a prominent feature. Hemorrhagic septicemia, therefore, is regarded as a misleading name for this disease. It is not uncommon to find pure or nearly pure cultures of Pasteurella in respiratory infections of young calves.
The most dependable diagnosis of Pasteurella multocida infection must employ the fermentation reaction on saccharose, lactose, rhamnose, xylose, and arabinose, along with the other biochemical reactions. The nonproduction of indole, the fermentation of lactose, and the hemolysis of blood are outstanding reactions of P. hemolytica.
27.3.12 Treatment
Therapeutic agents:
Apparently the Pasteurella are much more sensitive to antibiotic and sulfa drugs than other Gram negative organisms. Sulfamerazine has merit in the treatment of the disease. Reports on the efficacy of antibiotics vary, but penicillin, aureomycin, neomycin, terramycin, polymyxin B, chloromycetin and dihydrostreptomycin have been employed with success. Calves treated with terramycin and antiserum combinations are reported to have a dramatic recovery.
27.3.13 Biologics:
Bacterins.
These are cultures of the specific organism killed with heat or chemicals or a suspension of formalinized embryo in which the bacterium has been propagated. They may consist of the antigen absorbed on aluminum hydroxide from formalin killed cultures. These bacterins are used on cattle and sheep from 1-3 weeks prior to shipment in order to allow antibodies to form by the time they are needed.
Immune serums.
Two kinds of immune serum are available for treating animals in the early stages:
- (1) one made from cattle, and
- (2) one made from horses.
The homologous product should always be used since fewer serum reactions will be obtained following its administration. Large doses are effective in treating the affected animal in the early stages. Serum treatment may be used on a herd basis, but it is probably useless to give serum to an animal in which the pneumonia is fully developed.
Supportive treatment.
General supportive treatment as outlined in the treatment of pneumonia should be implemented. This may include oxygen where it is available, especially in the critical stage where anoxia is severe. Treatment with enzymes and expectorants have value in chronic cases. Affected animals should be housed in warm, draft-free accommodations, and provided with ample, fresh water, and light, nourishing food. Fluid therapy can be of value but must be given carefully, as overloading of the right ventricle may cause acute heart failure.
27.3.13 Control
There are no state or Federal regulations. Pretreatment of cattle destined for shipping with tranquilizing agents has been of some value. It is claimed that treated animals are more easily handled, adapt more readily to the feedlot environment, and show a lower incidence of infection.
27.4.1 Pasteurella tularensis
causes tularemia primarily in various rodents but especially the cotton tail rabbit. The organism caused infection in sheep in the western USA which were heavily infected with the wood tick. The wood tick had of course been feeding on wild rodents in which the disease was enzootic.
27.4.2 Pasteurella pseudotuberculosis
Causes plaquelike disease of guinea pigs, sometimes of rats, and occasionally of other rodents.
27.4.3 Pasteurella pestis
Cause of plaque or pest of man.
27.4.4 The Genus Hemophilus
This is a group of bacteria which require certain growth-promoting substances known as X-factor and V-factor. These substances are present in hemoglobin of animals and in the fresh juice of certain plants. Because of the stimulating effect of hemoglobin on these organisms, the name Hemophilus was created. The organisms are small, coccoid, nonmotile, nonsporeforming bacilli that are found for the most part in the respiratory tract of animals and man. These bacteria are frequently associated with the disease influenza; consequently they are often referred to as the influenza group.
Many of the species of this group are not significant as inciters of disease in animals and man. Some have been described by only a few investigators and are not considered of great importance. However, a few species are important factors in human and animal infections.
The species that are of particular interest in veterinary medicine are:
27.4.5 Hemophilus influenza
Associate with human influenza
H. suis - associated with swine influenza
H. canis - found in the preputial secretion of dogs
H. ovis - isolated from respiratory infections in sheep
H. cuniculi - found in subcutaneous abscesses of rabbits
H. gallinarum - associated with infectious coryza of fowl
The X-factor is now recognized as a catalase of beef liver or iron complex called hemin. Hemin is probably a necessary link in the synthesis of catalase. It can be replaced by cysteine, which reduces peroxide and makes catalase unnecessary.
The V-factor is recognized as Coenzyme I (diphosophopyridine nucleotide, DPN) which may be extracted from yeast, certain vegetable cells, and some bacteria, particularly Staphylococci.
The X-factor withstands moderate autoclaving; the V-factor is easily destroyed by heat.
The phenomenon of satellitism or satellite formation, is often exhibited by organisms of this group when inoculated on media containing the X factor but lacking the V factor, i.e. heated blood agar. Little or no growth will occur on such media except in the immediate neighborhood of colonies of other bacteria species (i.e., Staphylococci) which produce the V-factor which then diffuses into the surrounding medium.
This was described by Pfeiffer in 1892. It was isolated from the upper respiratory tract of a person suffering from influenza and was believed to be the cause of that condition. However, in the great pandemic of human influenza in 1918-19, it was discovered that Pfeiffer's bacillus was not invariably present in the disease, and it was shown by English and American workers that influenza was caused by a filterable virus. The influenza bacillus undoubtedly plays a secondary role in human influenza, and frequently has a part in the complications which so often develop, but true influenza can occur in its absence.
27.4.5.1 Morphology and Staining Reaction
Hemophilus influenza is a Gram negative, nonsporeforming, aerobic facultative bacillus. It is a tiny rod-shaped organism that may be quite pleomorphic. Some strains are encapsulated. In young cultures it usually appears as thin rods measuring about 0.2 microns in breadth and 0.50-2.0 microns in length. Long thread forms are seen frequently. Cultures older than 24 hours usually consist largely of coccoid elements, often arranged in large masses. Club-shaped forms and comma-shaped cells are also seen. The organism stains poorly with ordinary stains.
27.4.5.2 Cultural Features
The organism is highly parasitic and sensitive to all heat but body conditions. No growth is obtained on plain or glycerol-containing agar, in broth, gelatin, milk. potato, or egg media, or on coagulated blood serums, unless the growth factors X and V are added, usually in the form of fresh blood or blood extracts. Cultures must be incubated at 370C.
Agar slants to which 0.5-1.0 ml defibrinated blood has been added may be used for isolation. Another medium on which the organism will grow is chocolate agar. It is made by adding defibrinated blood to agar at a temperature of 70-800C.
The surface colonies of H. influenza are circular in outline, grayish, flattened, semi transparent, and have sharp edges. Under the most favorable conditions the colonies do not become larger than about 1 mm in diameter.
27.4.6.1 Synonyms:
Hemophilus influenza var. suis, hog flu
The organism was first described by Lewis and Shope in 1931. In subsequent studies, Shope showed that H. suis was relatively harmless to pigs when inoculated alone. It became highly pathogenic when inoculated along with a filterable virus causing what is termed swine influenza. Swine influenza is therefore a disease produced only by the concerted action of the bacillus and the virus.
27.4.6.2 Cultural Features
Hemophilus suis resembles H. influenza except that it is relatively inert biochemically and differs immunologically. Both X and V factors are required.
27.4.6.3 Pathogenicity
Hemophilus suis is only slightly pathogenic for normal swine. After internal installation a mild transitory illness sometimes occurs, but frequently there are no detectable symptoms. When illness is evident, the disease does not transmit to pen mates. However, when cultures of H. suis are added to the influenza virus (which alone will not cause serious illness) typical influenza results, and then the disease will transmit naturally.
The organism is not pathogenic for rabbits, guinea pigs, or white rats. It occasionally proves pathogenic for white mice.
27.4.6.4 Immunity
Swine which have recovered from attacks of influenza are immune. The presence of virus-neutralizing antibodies in the blood serum of these swine indicates that the immunity is a virus immunity and not related to H. suis. Hemophilus suis will not immunize swine against influenza. Although it is essential for the production of the disease, it is clear that the virus plays the important role. Therefore there are no available immunizing agents.
27.4.6.5 Diagnosis
The presence of H. suis can be detected only by demonstrating the organism by the inoculation of suitable culture media. For this purpose blood agar, chocolate agar or potato infusion media are recommended.
27.4.6.6 Antigenic Structure
The organism does not cross agglutinate with other strains of Hemophilus. The antigenic structure had not been determined. The organism does not produce a soluble toxin and is not hemolytic.
27.4.7.1 Synonyms: Glanders, Farcy
27.4.7.2 Etiology:
Glanders is an infectious disease produced Malleomyces mallei (Pseudomonas mallei). Though it is primarily a disease of solipeds (horses), it has occurred spontaneously in goats, sheep and domestic and wild carnivores that have eaten infected horse flesh. Man is quite susceptible, particularly when infection is acquired through cultivated material in the laboratory.
27.4.7.3 History
Glanders is one of the oldest known disease of horses, and at one time was wide spread throughout Europe, Asia, Africa, and to a lesser extent the Western Hemisphere. Through test and eradication methods, sanitation and veterinary surveillance, and because of the decrease in density of the horse population, the disease has been eliminated or controlled in most well-developed countries. Though it is rarely seen in America today, it should be remembered that glanders has not been eradicated. The causative agent, M. mallei, was first isolated in 1892.
27.4.7.4 Morphology and Staining Reaction
The pathogen is a slender, pleomorphic rod, varying from 0.3-0.5 microns in width and 1.5-5 microns in length. The ends are rounded, and the sides are irregularly parallel or wavy. The organism is Gram negative, but the stain is uneven and bipolar staining is quite common. It is nonmotile, nonencapsulated, and nonsporeforming.
27.4.7.5 Cultural Features
As a facultative anaerobe, M. mallei grows well on most common laboratory media, when incubated at 370C. It produces brown, amorphous, translucent colonies. No hemolysis is produced on blood agar.
27.4.7.6 Resistance
The organism is not especially resistant, and dessication in sunlight kills it quickly. A number of disinfectants, including benzalkonium chloride, iodine and mercuric chloride are effective. However, lysol and phenol are apparently ineffective. The organism can remain viable in water for at least 4 weeks.
27.4.8.3 Transmission
Infection is contracted in most instances through ingestion, although it probably can occur through inhalation and wound infection. From ancient to modern times, wars have always caused the disease to flourish, and the distribution of army animals to civilian services has served to spread the disease.
Clinical Features
In both the acute and chronic forms, the respiratory tract is the principal target. A cough and high fever reflect the fulminating bronchopneumonia that characterizes the acute form. This form is usually seen in asses and mules. In the horse, a more insidious, debilitating condition, coupled with chronic pneumonia and a purulent nasal exudate (often unilateral) is commonly encountered. The disease may occasionally assume a cutaneous form with swelling, indolent ulcers, and lymphangitis.
27.4.7.8 Pathogenicity
In the acute form, the lesions are attributed to septicemia and a diffuse severe catarrhal bronchopneumonia, while in the chronic form, the pneumonia is more miliary in nature, resembling tuberculosis. The organisms may be found in other organs such as the liver and spleen. Crater-like ulcers in the lymph nodes may discharge a thick exudate containing the organism; a condition known as Farcy.
27.4.7.9 Diagnosis
The organism can be found in impression smears made from fresh lesions, but demonstration of the organism in older lesions is difficult. Diagnosis must be based on demonstration; the presence of complement-fixing antibodies; or a positive reaction to mallein. Biochemically the organism is rather inactive. Demonstration of the presence of the organism is often based on a positive reaction to intraperitoneal infection of a small amount of suspect tissue into a male guinea pig. If M. mallei is present, an orchitis develops in 3-4 days. Unfortunately the reaction is not specific for M. mallei.
The Mallei test is based on a delayed hypersensitivity reaction, similar to the one used to diagnose tuberculosis. The reagent consists of an autoclaved filtrate from a broth culture of the organism, which after suitable dilution may be injected subcutaneously into the skin of the neck, or more often, intradermally into the skin of the eyelid. For a normal animal the test will give only a slight reaction. However, an animal with glanders will develop delayed hypersensitivity with symptoms of intoxication.
Subcutaneous injected in an infected animal will give rise to fever and swelling, while a normal animal will show only swelling. In an ophthalmically injected animal, a purulent infection occurs as the reaction in a few hours.
27.4.7.10 Immunity
No immunizing agents are available for the treatment and prevention of glanders. Animals that recover from natural infections are not solidly immune.
27.4.7.11 Treatment
It is not advisable to institute treatment in domestic animals. Sulfonamides have been shown to be effective in man.
27.4.7.12 Public Health
Man is not highly susceptible to glanders, yet numerous infections have occurred in persons caring for glanderous animals, especially stablemen and veterinarians. Glanders in man is characterized by pain at the point of infection, swelling of the area lymph nodes, development of nasal and mouth ulcers, development of abscesses and pustules in the skin, joint inflammation, and general symptoms accompanied by pain. Most cases usually end fatally in 2 to 4 weeks.
27.4.8.1 Synonyms: IBK, Pinkeye, Blight
27.4.8.2 Etiology:
There is a lack of specific information on M. bovis as the etiologic agent:
- 1. The identity of the organism is not clear. Certain other bacterial species are similar in general characteristics.
- 2. Attempts by many workers to experimentally reproduce
