Caseous lymphadenitis in goats & sheep Paul R. Earl Facultad de Ciencias BiolÃ³gicas Universidad AutÃ³noma de Nuevo LeÃ³n San NicolÃ¡s de los Garza, NL, Mexico email@example.com.
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Caseous lymphadenitis in goats & sheepPaul R. EarlFacultad de Ciencias BiológicasUniversidad Autónoma de Nuevo LeónSan Nicolás de los Garza, NL, Mexicopearl@dsi.uanl.mx
Introduction. Caseous lymphadenitis (CL) involves 1) prenatal intoxication causing immune tolerance, 2) respiratory paralysis, 3) the futility of vaccinating subclinically infected animals, many of which do not respond well immunologically, 4) involves treatment and 5) quarantine as needed for eradication.
The theme of perinatal CL is death by paralysis with many variations. In districts with CL, all goats and sheep may be infected as they are likely born tolerized to the toxin phospholipase D (PLD) and the other corynebacterial proteins. This means that the kids (cabritos) and lambs have no defense against prompt infections that can raise the blood PLD concentrations to lethal levels including demyelination analogous to diphtheric polyneuropathy.
Pathology.It is a false impression that CL in goats & sheep caused by Corynebacterium pseudotuberculosis and is confined to the lymphatic system, evincing abscesses and granulomas mainly seen in the skin. Grave lesions in the lungs are common. CL can be a permanent heritage rather than a chronic disease as the fetus is often exposed to and therefore tolerized by the toxin phospholipase D (PLD) and other corynebacterial proteins produced in its infected dam.
In some districts and countries like Mexico, all sheep and goats that have been inspected are or were infected. To vaccinate them as being disease-free is a traditional mistake. The cabrito can acquire immune tolerance. Many neonatal cabritos intoxicated with PLD are infected from their dams’ milk, feces in the corrals or from other goats with the production of more PLD leading to paralysis and death. That is, many tolerized cabritos born intoxicated with PLD never reach market age of 1 to 3 months, dying of asphyxiation that is almost always undiagnosed. This is respiratory muscle dysfunction.
An unusual but wellknown situation is exemplified. A truckload of 600 cabritos arrived in Monterrey, NL after a 6-hour ride at 8 o’clock of a hot day. All were dead. This is why slaughter is at night, and trucks start off after 6 o’clock, arriving at times like 4 AM. Asphyxiation was credited to the heat, and of course goatraisers do not know about PLD. In one ranch, 352/352 cabritos of a herd of 500 goats died, and complete wipeouts are common. The majority might pass as cases of pneumonia, but actually death is by paralysis involving the demyelination of the nerves to the diaphragm.
Furthermore, C. pseudotuberculosis has been long known to infect horses and cattle. Infections in man are known for over 50 years Still, it is not always clear that Corynebacterium sp. rather than Actinomyces sp. was the cause. Hemolysis with catalase Identification of orynebacterium pseudotubercul-osis. It is Gram-positive and catalase positive, usually a bacillus, but on solid agar it can grow as a coccoid.
Biochemical tests that are suggested for coryneform bacteria are: 1) catalase, 2) nitrate, 3) starch, 4) pyrazinamide, 5) esculin, 6) mannose, 7) mannitol, 8) ribose, 9) trehalose, and 10) xylose.However, many more tests might well be added.
Treatment. Animals can be successfully treated orally with penicillin G, and oral tetracycline is a second choice on alongterm basis such as 2-3 months of treatment. However, encapsulated abscesses (“cheesy glands”) have to be removed or cleaned out surgically. Rose-red abscesses should have the circulation needed for antibiotic treatment.
In common texts, antibiotic treatment is discouraged unfortunately as blocked circulation is considered. Treatment lowers the PLD levels. Negative levels will change to positive antitoxin levels with successful penicillin since PLD production by the bacteria is then stopped while antibodies are being produced. By a negative antitoxin level is obviously meant a positive toxin titer. The cabrito that is born intoxicated has a positive toxin level Nonetheless, the textbook advice could imply that difficult treatment costs more than the patient.
Vaccines. Human and animal health vaccines dating from Louis Pasteur have had enormous success in disease prevention. Diphtheria by Corynebacterium diphtheriae is among these famous diseases. Nevertheless, CL vaccines have consistently failed via not recognizing immune tolerance for PLD and other proteins of Cps. There are also a large number of antecedent works, all to be graded as failures, because survivors have often been taken as uninfected, and the antibody status of the host before and after vaccination was not given. Toxin in the blood should be searched for.
The futility of vaccinating an infected and thereby PLD-intoxicated animal has not always been wisely taken into account. The effect of the first vaccination can often be that of a booster when antitoxin is detectable.. Nonetheless, the health status of each goat or sheep against CL is not usually known, and in particular its CL immune state is unknown.
Immune tolerance.The goat says to the veterinarian, “You are vaccinating me against me!” The goat is wrong, but recognized PLD and other CL proteins as self.It is wellknown that immunosuppressed animals and man may succumb to other diseases. In addition, sheep & goats infected with CL do suffer accidents. Injections lend towards hysteria in them or considerable stress.
The intoxicated and thus tolerized newborns soon to be infected are not recognized by most veterinarians who believe that skin abcesses and swollen lymphatics are the main indicators of the disease prevalence. This misdiagnosis encourages vaccination campaigns with unresponsive animals.
Eradication.PLD production in the infected dam can be stopped by treatment with penicillin G as formulated in some milk replacers sometimes used to protect calves. Tetracycline is a second choice by cost and oral administration. However, treatment for elimination of CL has never been tried on a respectable scale. When the infected dam receives an antibiotic throughout pregnancy, the fetus is not tolerized, and the newborn will receive passive immunity from colostrum and milk, i. e., is protected against CL.
Nonetheless, cabritos should have some access to antibiotics in milk replacers. This has never been seen in the field since often owners cannot find such milk replacers even if they were willing to pay for them. Again, the normal state is assumed when the infected state is factual. Mexican goatraisers are losing more than 10 millions of dollars a year, essentially because the problem is unrecognized. The problem is bacterial PLD production and all its attributes including low level immune responses.
Goats, a symbol of poverty, are raised in a subsistance no-cost system, yet have a high labor requirement, and expected facilities like a watering trough can be missing in the barren corrals. If by cost and lack of facilities, the dams are not to be treated, the cabritos can be by using an antibiotic milk replacer. One hundred replaceable plastic nipples can be placed along a large plastic pipe to hold the milk replacer (50 nipples on each side). This two-times per day feeding system will save cabritos.
Toxicosis again.Complete wipeouts with CL deaths of all cabritos are recurrent events. Goat owners usually do not keep records and soon forget catastrophic animal losses that they always accept fatalistically. Fatalism widens the gap between traditional losses and technical prevention. The last question is: Who will pay for prevention?
The goat or sheep in repose may not be able to get up, because of paralysis in the limbs and the diaphragm, and very likely will die. This condition is likely to be repiratory muscle dysfunction. It cannot reach food or water. yet may refuse them. Importantly, seasonal starvation by drought or winter enter this panorama which of course includes other infectious diseases and common parasitoses.
Erradication is the ultimate form of prevention and depends on 1) longterm antibiotic treatment, 2) quarantine and 3) vaccination of competent animals as well as veterinary monitoring of ranches over perhaps several decades and extending to millions of goats and sheep. Clearly, erradication is both costly and slow, likely radiating from some center that has been freed of CL. However, it is crystal clear that vaccinating unresponsive animals must fail to prevent CL which is already subclinical in them.
How to raise cabritos.The infected dams must receive penicillin G to normalize their immune status so that a passively immune cabrito is obtained. The cabrito must be removed from its mother at birth to enter a clean environment and then to be raised on antibiotic milk replacer, if it is retained by the ranch. At 1 month of age if it has PLD neutralizing antitoxin, it can be vaccinated with a killed vaccine (toxoide).
In conclusion, CL should be recognized as a paralyzing toxicosis rather than as a necrotizing skin disease. It can be controlled or eliminated by oral penicillin G, or other antibiotics. Cabritos can be saved by giving them antibiotics in milk replacers with but also without removing them from their infected dams at birth. Vaccine success depends on the immune response rather than on the vaccine qualities. The cessation of PLD production in the infected host allows the antitoxin expression. Ongoing vaccine campaigns as in Brazil are presumed to fail since all others have, mainly because immune tolerance does not allow protective host responses.