Date: Thu 10 Mar 2016
Source: The Guardian [edited]
Some 9 cattle have recently died in Belize as a result of both rabies and blackleg [_Clostridium chauvoei_] diseases. There have been at least 3 cases of rabies among cattle in the Orange Walk and Cayo districts and several cases of blackleg have been clinically diagnosed in the Toledo district. There is now a concurrent infection among cattle with rabies and blackleg and from previous years it has been known that in the starting of every year, cattle would come down with blackleg. As a result, the Belize Agriculture Health Authority, BAHA, is now recommending that farmers purchase the vaccines that can be used to prevent both diseases from occurring. BAHA has since been having meetings with the Belize Livestock Producers Association.
A specially assembled team has also been meeting with cattle farmers. In collaboration with the Ministry of Agriculture, a team travelled last week to the Toledo District and have been getting positive response from cattle farmers. BAHA strongly recommends for all cattle farmers to vaccinate their cattle against rabies if they have not been vaccinated in the last year and against blackleg if they have not been vaccinated in the last 6 months. Rabies is a highly fatal disease that affects all mammals. The disease is always fatal but can be prevented through vaccination. Affected animals will usually show nervous signs and aggressive behaviour.
Most animals will show excessive salivation as swallowing becomes impossible. The rabies virus infects the central nervous system, ultimately causing disease in the brain and death. Avoid coming in contact with animals showing these symptoms and immediately call BAHA Officers. An advisory from BAHA notes that blackleg is a highly fatal disease in young cattle. In most cases the animal is found dead without being previously observed sick. The speed with which blackleg kills usually makes individual treatment useless. It is caused by the spore forming, rod shaped, gas producing bacteria _Clostridium chauvoei_.
The spores of the organism can live in the soil for many years. The 1st sign observed is usually lameness, loss of appetite, rapid breathing, and the animal is usually depressed and has a high fever. Characteristic swellings develop in the hip, shoulder, or elsewhere. First the swelling is small, hot, and painful. As the disease progresses, the swelling enlarges and becomes spongy and gaseous. If you press the swelling, gas can be felt under the skin. The animal usually dies in 12 to 48 hours. Dr Miguel DePaz, the Director of the Animal Health Department within BAHA recommends that farmers should vaccinate their cattle every year. He reasons that farmers can obtain up to BZD 2400.00 [about USD 1200] from an 800 pound [363 kg] animal, so spending BZD 5.00 [about USD 2.50] on a rabies vaccine and BZD 1.50 [about USD 0.75] for a vaccine to fight blackleg is cost effective. These vaccines can be obtained at any agro veterinary store or from a registered veterinarian. Blackleg is almost entirely preventable by vaccination.
The most commonly used clostridial vaccination in cattle is the 7-way type, which protects against 7 types of clostridia organisms. Additional information can be obtained from livestock officers of the Department of Agriculture in the districts, BAHA animal health officers, Belize Livestock Producers Association, and Registered Veterinarians. -- Communicated by: ProMED-mail <firstname.lastname@example.org> [It is unclear if the cattle had both diseases or there were herds with both diseases. I think the latter is more probable but the former is a possibility. Blackleg is an acute, febrile, highly fatal disease of cattle and sheep caused by _Clostridium chauvoei_ and characterized by emphysematous swelling, commonly affecting heavy muscles (clostridial myositis). It is found worldwide. _C. chauvoei_ is found naturally in the intestinal tract of animals. Spores remain viable in the soil for years and are purported to be a source of infection. Outbreaks of blackleg have occurred in cattle on farms in which recent excavations have occurred or after flooding.
The organisms probably are ingested, pass through the wall of the gastrointestinal tract, and after gaining access to the bloodstream, are deposited in muscle and other tissues (spleen, liver, and alimentary tract) and may remain dormant indefinitely. In cattle, blackleg infection is endogenous. Lesions develop without any history of wounds, although bruising or excessive exercise may precipitate disease in some cases. Commonly, the animals that contract blackleg are of the beef breeds, in excellent health, and gaining weight. Outbreaks occur in which a few new cases are found each day, sometimes for several days.
Most cases are seen in cattle from 6-24 months old, but thrifty calves as young as 6 weeks and cattle as old as 10-12 years may be affected. The disease usually occurs in summer and fall and is uncommon during the winter. Usually, onset is sudden, and a few cattle may be found dead without premonitory signs. Acute, severe lameness and marked depression are common. Initially, there is a fever but, by the time clinical signs are obvious, body temperature may be normal or subnormal. Characteristic edematous and crepitant swellings develop in the hip, shoulder, chest, back, neck, or elsewhere. At first, the swelling is small, hot, and painful.
As the disease rapidly progresses, the swelling enlarges, there is crepitation on palpation, and the skin becomes cold and insensitive with decreased blood supply to affected areas. General signs include prostration and tremors. Death occurs within 12-48 hours. In some cattle, the lesions are restricted to the myocardium and the diaphragm. A rapidly fatal, febrile disease in well-nourished young cattle, particularly of the beef breeds, with crepitant swellings of the heavy muscles suggests blackleg. The affected muscles are dark red to black and dry and spongy, have a sweetish odor, and are infiltrated with small bubbles but little oedema.
The lesions may be seen in any muscle, even in the tongue or diaphragm. In sheep, because the lesions of the spontaneously occurring type are often small and deep, they may be overlooked. Occasionally, the tissue changes caused by _C. septicum_, _C. novyi_, _C. sordellii_, and _C. perfringens_ may resemble those of blackleg. At times, both _C. septicum_ and _C. chauvoei_ may be isolated from blackleg lesions, particularly when the carcass is examined ~24 hours after death, which allows time for postmortem invasion of the tissues by _C sordellii_. Field diagnoses are confirmed by laboratory demonstration of _C. chauvoei_ in affected muscle (standard methods: culture and biochemical identification). The samples of muscle should be taken as soon after death as possible.
The fluorescent antibody test for _C. chauvoei_ is rapid and reliable. A PCR is available and reported to be very good for clinical samples but not for environmental samples. A multivalent vaccine containing _C. chauvoei_, _C. septicum_, and, where needed, _C. novyi_ antigens is safe and reliable for cattle and sheep. Calves 3-6 months of age should be vaccinated twice, 4 weeks apart, followed by annual boosters before the anticipated danger period (usually spring or early summer). In an outbreak, all susceptible cattle should be vaccinated and treated prophylactically with penicillin (10,000 IU/kg, IM) to prevent new cases for as long as 14 days. Cattle should be moved from affected pastures. Vaccine failure has been observed locally and attributed to a deficient spectrum of antigens in the vaccine. In such instances, a bacterin vaccine is produced with local, previously identified clostridial strains of C chauvoei.
This comment was extracted from <http://www.merckvetmanual.com/mvm/generalized_conditions/clostridial_diseases/blackleg.html
Rabies transmitted by vampire bats has existed in tropical America since the pre-Hispanic era. Originally the epidemiological cycle of the disease involved mainly wildlife, with the vampire bat being the main vector of the disease and the wild mammals of the region its victims. With the arrival of domestic mammals and with the European conquest and colonization, the vampire bat changed its feeding habits, preferring to feed on domestic mammals, especially cattle. Since the vampire bat is a very effective vector of the rabies virus, vampire-transmitted rabies became a very important limiting factor for the development of livestock production in most countries of Latin America and the Caribbean.
Vampire bats preferentially prey on livestock. Livestock and horses are generally larger than indigenous wildlife prey species, are more abundant and tend to stay in the same location for extended periods. Once a colony of vampire bats has located a herd of animals, they are then able to return to the same herd on subsequent nights. This is particularly true for cattle. Humans have also provided vampire bats with roosting sites in the form of buildings, bridges, and wells. This in turn has contributed to an increase in the number and size of vampire bat colonies, and enlarged the population that can act as a reservoir for rabies virus. Deforestation, a consequence of land clearance for logging and modification for agriculture has simultaneously reduced the numbers of natural prey species and brought vampire bats into contact with livestock and man.
Bovine rabies in Latin America is commonly called derriengue, a Spanish word for a fatal paralytic disease. The infected animals exhibit signs of restlessness or excitement with sudden onset of hind limb paralysis. This progresses to the fore limbs. Overt salivation is commonly observed but is believed to be due to difficulties in swallowing rather than excess saliva production. Emaciation in animals that survive for any length of time is observed but the disease is invariably fatal.
There are 3 species of blood-feeding or hematophagous bats found exclusively in Latin America. Only one of these, the common vampire bat _Desmodus rotundus_, is a well known reservoir for rabies. Vaccination of cattle is a very successful way of preventing rabies in cattle. Extracted from <http://www.mdpi.com/1999-4915/6/5/1911/pdf
>. Ultimately both of these diseases may be prevented by vaccination. - Mod.TG] [Maps of Belize can be seen at <http://www.lib.utexas.edu/maps/americas/belize_pol_03.jpg
> and <http://healthmap.org/promed/p/19
>. - ProMED Sr.Tech.Ed.MJ]