When Dr Mokhtar asked about what is the common diseases in goat I simply answered CLA! but then I realized CLA is just the term I often heard when we talk about goat but never looked detail about it.
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CLA in goat
Caseous Lymphadenitis (commonly referred to as "CL"), is a chronic lymph node abcess that is caused by the organism corynebacterium pseudotuberculosis. It is a contagious bacterial infection in goats (and sheep). Infection occurs through wounds caused by head butting, punctures, and shearing, as well as by oral ingestion of the exudate (pus) from an abscess that has ruptured. The lymph system filters the bacteria from the goat's body and pushes it outside into thick-walled encapsulated abscesses so that it can't harm the goat.
Infection occurs after C pseudotuberculosis penetrates through unbroken or abraded skin or through mucous membranes. Most infections occur through wounds contaminated with purulent exudate from ruptured external and pulmonary abscesses. Contaminated dipping vats and shearing, handling, and feeding equipment are responsible for spread of the organism, along with confinement housing at high stocking densities.
The pus contains large numbers of bacteria that can survive for months in hay, shavings, and soil. The disease is most often introduced into a flock by entry of an apparently healthy carrier from an infected flock, by contact on shared pastures, or via contaminated fomites such as shearing equipment.
Dairy goats have had a higher incidence of CL than meat breeds, primarily because the penned method of raising dairy animals gave rise to easier transmission of the bacterium from goat to goat. However, the use of dairy does as recipients for Boer embryos has facilitated the spread of CL, and crossbreeding dairy animals with meat goats has taken it a step farther.
Because the thick pus is enclosed in a tough fibrous capsule which medicine cannot penetrate, antibiotic treatment is ineffective against the CL bacteria. Caseous Lymphadenitis is currently considered incurable.
**From Merck Veterinary Manual
Lesions
Caseous lymphadenitis is a chronic, recurring disease. A slowly enlarging, localized, and nonpainful abscess may develop either at the point of entry into the skin or in the regional lymph node (superficial or external form), from which it may spread via the blood or lymphatic system and cause abscessation of internal lymph nodes or organs (visceral or internal form).
Initial infection may cause no clinical signs or may be accompanied by high fever, anorexia, anemia, and cellulitis at the infection site. Superficial abscesses enlarge and may rupture and discharge infectious pus. In sheep on range, most superficial abscesses develop in the prescapular and prefemoral region, with transmission probably occurring when the flock is gathered for group treatments such as shearing.
In housed goats and sheep, superficial abscesses develop mainly in the head and neck region, likely due to transmission by contaminated feed, feeders, and other fomites. Animals with superficial abscesses show no obvious ill effects unless the location of the abscess interferes with functions such as swallowing or breathing. Abscessation may recur at the same site. Internal abscesses should be considered as a potential diagnosis for “thin ewe syndrome,” in which an adult small ruminant loses condition in the face of adequate nutrition. The visceral form is usually more extensive in sheep than in goats, mostly involving abscesses of the pulmonary parenchyma and mediastinal lymph nodes.
Other less common manifestations include caseous bronchopneumonia, arthritis, abortion, CNS abscessation often occurring in the pituitary gland, abscessation of a vertebral body causing paresis or paralysis, scrotal abscessation, and rarely, mastitis. Scrotal (inguinal) abscesses can cause temporary infertility in rams. The incidence of abscesses steadily increases with age; clinical disease is more prevalent in adults, and up to 40% of animals in a flock can have superficial abscesses.
Lesions
The typical gross lesion is a discrete abscess distended by thick and often dry, greenish yellow or white, purulent exudate. In sheep, the abscess often has the classically described laminated “onion-ring” appearance in cross section, with concentric fibrous layers separated by inspissated caseous exudate. In goats, the exudate is usually soft and pasty.
Clinical signs
Most commonly, symptoms are palpable enlargements of one or more of the superficial lymph nodes. The morbidity of the infection rate in goat flocks increase with age, and may approach 70%.The enlarged lymph nodes have a very thick wall and are filled with thick greenish pus. The most common lymph nodes affected are mandibular, prescapular (B), prefermoral (C), and supramammary (D) lymph nodes. Less common is involvement of lymph nodes internally in the chest and abdomen. As the animal gets older, abscesses often develop around the lungs, heart, liver, kidney, and spinal cord. They may cause weight loss, pneumonia, and neuoligical signs.
Location of common swelling caused by CLA
Diagnosis
1. Presence of a firm to slightly soft subcutaneous swelling in the location of a lymph node
2. Herd history of CL.
3. Culture: aspiration of the swelling and sending it to the diagnostic lab for isolating and identifying the organism.
4. Serology: serologic tests such as bacterial agglutination test and synergistic hemolysis - inhibition test are valuable in identifying goats with early stage of the disease (no abscess yet developing).
**Serologic testing may not be accurate due to the presence of antibodies in previously exposed non-diseased or from cross - reactivity of diagnostic antigens with antibodies against other bacteria
1. Separate and isolate the affective animals.
2. Ripened abscesses lanced and flushed with 7% iodine solution.
3. The pus should be flushed down a drain, or collected and burned.
4. Wear gloves to prevent skin infections in humans.
5. Wash hands well after handling infected animal.
6. Surgical removal of the encapsulated abscess offers the advantages that the treated animals need not be quarantined.
7. antibiotic treatment has not been effective
** Commercial vaccines, currently only licensed for use in sheep, reduce the incidence and prevalence of caseous lymphadenitis within a flock, but they neither prevent all new infections nor cure animals already infected. Vaccination should start in young stock after colostral immunity has waned (~3 mo of age).
Colostral immunity can be improved by administering a booster to pregnant ewes and does 1 mo prior to lambing/kidding. A primary series (2 injections, 4 wk apart) is required in young stock or previously unvaccinated adults; repeat vaccination at least annually will help reduce the prevalence of disease.
Vaccination will not cure existing infections, so it is important to ensure that animals are well vaccinated prior to exposure. These vaccines should be used with caution in potentially infected goats, as adverse reactions are sometimes reported.
Control
1. Vaccinating, culling, and reducing exposure to potentially contaminated fomites, such as shearing blades, dipping fluids, feeders, and feed. Eradication is difficult and requires strict biosecurity and vaccination protocols and rigorous culling of all infected animals. Once the disease is at a low prevalence, vaccination should be stopped and all seropositive, nonvaccinated animals culled.
2. Prevention of disease entry into a clean flock is based on serologic screening and isolation of incoming animals. Seropostive unvaccinated animals should not be accepted into the flock.
Colostral immunity can be improved by administering a booster to pregnant ewes and does 1 mo prior to lambing/kidding. A primary series (2 injections, 4 wk apart) is required in young stock or previously unvaccinated adults; repeat vaccination at least annually will help reduce the prevalence of disease.
Vaccination will not cure existing infections, so it is important to ensure that animals are well vaccinated prior to exposure. These vaccines should be used with caution in potentially infected goats, as adverse reactions are sometimes reported.
Control
1. Vaccinating, culling, and reducing exposure to potentially contaminated fomites, such as shearing blades, dipping fluids, feeders, and feed. Eradication is difficult and requires strict biosecurity and vaccination protocols and rigorous culling of all infected animals. Once the disease is at a low prevalence, vaccination should be stopped and all seropositive, nonvaccinated animals culled.
2. Prevention of disease entry into a clean flock is based on serologic screening and isolation of incoming animals. Seropostive unvaccinated animals should not be accepted into the flock.
3. Remove young stock at birth and rearing separately from the infected flock has been shown to be an effective means of eradication. The infected flock is then culled as quickly as economics allow.
4. Prevention of CLA in an uninfected flock involves shearing biosecurity and purchase only of uninfected replacement stock.
5. Producers should purchase their own shearing equipment and not share it with other flocks.
6. Shearers should arrive at the flock wearing clean footwear and clothing. Wool bags, shearing boards, moccasins, hands, clothing, and all parts of clippers can be a source of bacteria. If there is a break in biosecurity, disease usually shows up 1-3 mo after exposure, or longer if the initial abscesses are internal or are missed.
Sources: Merck Veterinary Manual, CLA L. Dawson, CLA Suzanne W. Gasparotto
Sources: Merck Veterinary Manual, CLA L. Dawson, CLA Suzanne W. Gasparotto
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