|Article Index||"Caseous Lymphadenitis and Pinkeye"||Article Index|
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|CASEOUS LYMPHADENITIS AND PINKEYE||
1) Goats, like all other food animals, are plagued by numerous infectious diseases which reduce their productivity and profitability. Infectious diseases are ailments produced by microscopic organisms as a result of their existence and replication in the tissues of the host. These microorganisms are really parasites but the term ''parasite'' is commonly reserved for larger multicellular organisms such as lice, mites, flukes and various gastrointestinal worms. Thus, infectious diseases are commonly distinguished from parasitic diseases but also from metabolic diseases, nutritional diseases, toxic diseases, neoplastic diseases, etc. Infectious diseases are not necessarily communicable, that is, transmissible from animal to animal. Tuberculosis for example, is caused by a bacterium, Mycobacterium tuberculosis and is readily spread from man to man or animal to animal. Tetanus (lockjaw), on the other hand, although caused by a bacterium, Clostridium tetani, is not transmissible from animal to animal. It is associated with contamination of deep, penetrating wounds and is caused by a toxin elaborated by the organism.
2) Infectious diseases can be broadly subdivided as specific diseases caused by specific microorganisms (e.g. brucellosis: Brucella melitensis) and non-specific diseases such as mastitis, pneumonia, etc. which can be caused by a variety of different kinds of microorganisms. Mastitis for example, may be caused by staphylococci, streptococci, enteric bacilli, yeast, corynebacteria, etc.
3) Infectious diseases can also be subdivided according to the type of microorganism responsible for the infection, e.g.:
2. fungal: ringworm
3. bacterial: tuberculosis, brucellosis, caseous lymphadenitis, arthritis, Johne's disease
4. mycoplasmal: pleuropneumonia, arthritis
5. rickettsial: pinkeye
6. chlamydial: abortion, arthritis
7. viral: contagious ecthyma (sore mouth), arthritis
4) Mycoplasma, chlamydiae, and rickettsia are bacteria-like organisms. Mycoplasma will grow on special artificial media. Chlamydiae and rickettsia are also bacteria-like but, like viruses, can only replicate in living hosts.
5) No matter what causes a particular infectious disease, the eventual outcome of that infection is influenced by a number of different factors. Certain parameters of the host, the environment, and of the infecting microorganism are important.
6) With regards to the host, the integrity and preparedness of the immune system are critical. Some animals are born with defects of the immune system which make them unable to combat infectious diseases. Some animals are genetically endowed with superior resistance to infection; others are not. The newborn animal which receives passive immunity via maternal colostrum (first milk) is in an enviable position since it has a temporary protection against the microorganisms in its immediate environment at a most vulnerable time. Age of exposure is an important host factor since young animals are almost always more susceptible than older ones. In addition, poor nutrition can adversely influence an animal's resistance as can the presence of a concurrent illness or parasite infestation.
7) The nature of the environment can also have a profound effect on the outcome of a disease process. Cleanliness and adequate ventilation can reduce exposure to disease-producing organisms and prevent contamination build-up. Population density is also important since overcrowding almost invariably leads to disease problems. With infectious diseases in particular, the interchange of populations of animals is apt to be troublesome. Many cases of infectious disease outbreaks can be traced to the introduction of new animals into a herd. Such animals may appear healthy but may be incubating a disease or may be carriers of microorganisms to which the main herd has not been exposed. Of course, transfer of infection can also occur from the herd to the new animals.
8) Finally, there are factors associated with the infectious microorganisms themselves which can influence the nature of the disease produced. The virulence is genetically determined so that within a particular species of bacterium, there are a number of strains which vary in their ability to cause severe, even fatal disease. The dose of microorganisms involved is obviously important. In a contaminated environment, exposure to many microorganisms is more likely to result in a serious infection. A microorganism which can live peacefully if applied to the skin might wreak havoc if introduced to the lungs or mammary gland.
9) There are many infectious diseases of goats, even though goats as a species have not been well-studied from the infectious disease point of view. As goats are more intensively reared and investigated, new disease problems will undoubtedly be discovered. A brief discussion of some of the more important infectious disease problems of goats follows.
10) Caseous Lymphadenitis Caseous lymphadenitis, also called pseudotuberculosis or merely ''abscesses'' has been referred to as the curse of the sheep and goat industry throughout the world. It is considered by some to be the major disease problem of dairy goats in the United States. The causative agent, Corynebacterium ovis, also called C. pseudotuberculosis, was first described in 1894 from the same disease in sheep. It is a small rod-shaped bacterium which is colored blue (Gram +) by the common differential stain used in bacteriology. C. ovis grows readily on sheep blood agar and other bacteriological media enriched with serum. The organism forms small, dry, white to yellow colonies which are initially very tiny but grow to a pin-head size in about 48 hours. If an abscess has not ruptured and is lanced in a sterile fashion, pure cultures of C. ovis are commonly obtained from the pus.
11) The pus is thick, often dry, and greenish-white in color. Its consistency is best likened to toothpaste or putty. The abscesses formed by C. ovis are usually associated with lymph glands and may be ''external'' where they handily break to the outside or internal where they are not at all visible. In the goat the external abscesses of C. ovis are most often found around the head and neck, frequently below the ear and behind the jaw. They are initially small but invariably grow larger. Because the goat often manages to put a thick connective tissue wall around them, they do not readily rupture until they reach the size of walnuts or larger.
12) Internal lymph gland involvement often affects the mediastinal (between lungs), gastrohepatic (between stomach and liver) and mesenteric (intestinal suspensory) areas. Interference with organ function in these vital areas produces unthrifty and weakened animals which are frequently afflicted with difficult breathing and a chronic cough.
13) Much of our knowledge of caseous lymphadenitis comes from the experience of Australian workers with the disease in sheep. They found that environment contamination with C. ovis was common in afflicted herds and that the widespread distribution of abscesses in the species could be related to contamination of shearing wounds. The distribution of most external abscesses about the neck and head suggests that goats are most commonly infected via ingestion of the organism. Frequently goats are exposed as kids but abscesses don't become evident until the animals are at least a year of age. The disease is insidious in its development.
14) Clinical Signs To minimize environment contamination, encapsulated abscesses should be drained before they rupture. The hair should be clipped away around the abscess and its surface disinfected with tincture of iodine or other suitable antiseptic. The abscess should be incised vertically to promote drainage and pus should be squeezed out and collected for destruction by incineration or exposure to strong disinfectant solutions. Since C. ovis has been associated with infections in man, care should be taken to avoid direct exposure to the pus.
15) Following drainage, the affected goat should be isolated from other goats until healing is well-progressed. The wound should be irrigated initially and on a daily basis with an antiseptic solution such as chlorhexidine (''Nolvasan'') diluted 1:10 in hydrogen peroxide. Intramuscular application of penicillin - streptomycin on a daily basis for at least 3 days can minimize complications and continued shedding of the organism. Because of the presence of veins, nerves, arteries, esophagus, and glands in the throat region, abscesses in this area may require professional assistance in lancing. ''Throatlatch'' abscesses are especially serious and endanger the life of the affected individual.
16) Once established in a herd, caseous lymphadenitis is difficult to eliminate. Even goats in which abscesses are properly lanced and treated will often have recurrences, and environmental contamination leads to infection of kids. To remove caseous lymphadenitis as a herd problem, it is best to cull chronically affected goats. Kids should be separated from infected does at birth, given colostrum from clean does, and raised in a clean area on ''clean'' milk or replacer. Some experienced goat people have recommended the administration of bacterins made from C. ovis isolates from the herd in question but this practice remains controversial since no clearly definitive scientific studies have been made. Dr. Sam Guss, the eminent goat veterinarian, recommends initial application of an autogenous bacterin at 3 weeks of age, a second dose at 5 weeks of age, and booster doses at 3 to 6 month intervals thereafter. Lastly, the importance of cleaning and disinfecting premises before repopulation must be emphasized.
17) A bacterin is a young broth culture of C. ovis which has been inactivated with a dilute formalin solution. In this way the organism and its exotoxin are destroyed while the constituents which serve to stimulate the immune response are still active. Bacterins in theory should cause previously unexposed animals to more effectively resist natural infection or infected animals to more readily purge themselves of infection. The difficulty with C. ovis is that infected goats seem to have the ability to wall-off the organism temporarily but mobilize an immune response inadequate to effectively destroy it. Accordingly, recurrent abscessation is common.
18) Bacteria other than C. ovis may be responsible for abscessation as a result of contamination of lacerations or punctures. These are usually associated with poor sanitation. Corynebacterium pyogenes is frequently responsible for abscesses containing yellowish pus of a mayonnaise consistency. Streptococci often produce a watery discharge while staphylococci cause a creamy exudate. Although the nature of the pus can give clues to the cause of a particular abscess, only laboratory cultural methods can give definite information. Commercial bacterins against C. pyogenes and Pasteurella species are available and have been used prophylactically against pneumonia (which often accompanies the stress of shipping) and even against caseous lymphadenitis. Varying degrees of success have accompanied their use but, again, their real value is not well-established.
19) Pinkeye Infectious keratoconjunctivitis or pinkeye is a disease which usually appears in hot dry weather and is spread by close contact and flies. The cause is not definitely established in goats but rickettsia are believed to be involved in some cases and mycoplasma in others. The eyes are afflicted with excessive tearing, reddened mucous membranes, then a white discoloration of the cornea which obscures vision. In severe cases the cornea ulcerates and loss of the eye may result. In most cases, when the goats are protected from sunlight and given good nursing care, recovery is usual. Nevertheless, all goats, even those not affected, should be treated with broad spectrum antibiotic ophthalmic powders or ointments to minimize the spread of infection. Resistant carrier animals may serve as the source of the organism when dry, dusty, sunny days predispose a herd to the disease.
About the author: Extension Goat Handbook - This material was contributed from collections at the National Agricultural
Library. However, users should direct all inquires about the contents to
authors or originating agencies.|
J. M. Gaskin; U. of Florida, Gainesville
S. B. Guss; Pennsylvania State U., Unversity Park.
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