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Vra die veearts - Anthrax in cattle

Written by  Joan van der Poel
| in Veearts
| May 30, 2014

The disease, Anthrax, is caused by Bacillus anthracis, a spore forming bacteria.

It affects mostly herbivores, domestic as well as wildlife. In these animals it causes very acute illness with a high fatality rate. It is also seen in dogs, humans, pigs and horses, but is usually much less acute.  

Spores remain infective in soil for decades and may infect animals grazing there. In an outbreak biting flies may mechanically transmit spores between animals. Where feed is contaminated with meat or bone meal from animals which have died of anthrax, it can infect livestock. Hay may also be contaminated with infected soil. Carnivores and omnivores, including humans, may become infected through eating raw or poorly cooked contaminated meat.
    The disease occurs worldwide but is more commonly seen in regions with neutral or alkaline calcareous soils. Here epizootics periodically emerge among livestock and game, usually in association with drought, flooding or soil disturbance.  Sporadic cases occur between epidemics and maintain soil contamination.
    After spores enter the body, they first infect macrophages, one of the body’s defence cells. Here they germinate and multiply, usually at the site of infection and the closest lymph nodes. Toxin is produced which causes tissue death, and swelling. As bacteria spread through the body and release more toxins, generalised tissue damage and organ failure follow. After death, exposure to oxygen causes the vegetative bacteria to sporulate. For this reason it is best to avoid doing a post mortem. In an unopened carcass, vegetative bacteria will die due to pH changes in the carcass. However, discharges from body openings, bloating, scavengers, etc. may cause spore formation.

Clinical Findings
    The incubation period is 3–7 days (range 1−14 days). In cattle and sheep the clinical course is usually peracute and fatal. Staggering, dyspnea, trembling, collapse, a few convulsive movements, and death may occur in cattle, sheep, or goats with only a brief illness. Often animals are found dead without signs being observed. Body temperature is up to 41.5 degrees Celsius. Bloody discharges are often seen from the body openings after death. In some infections, severe swelling may be seen, especially of the lower neck, chest and shoulders.

    After death the carcass does not stiffen as normal. Rigor mortis may be absent or incomplete. Dark blood may be observed oozing from the mouth, anus and nostrils. Bloating and decomposition is rapid.  At this stage anthrax should be considered and blood smears taken with care.
    If the carcass is opened, blood will be dark and thick but not clotted. Bleedings will be visible on the surfaces of the abdomen and chest and heart. Red tinged fluid is present. The spleen will be enlarged, dark and soft. Liver, kidneys and lymph nodes are enlarged and dark red due to congestion.
    Blood smears are most often used to confirm the disease, but false positives are possible. Other conditions that cause acute death may be mistaken for anthrax. Consider lightning strike, bloat, clostridial infections, bovine babesiosis  and lead poisoning amongst other differential diagnoses.
    All livestock in endemic areas should be vaccinated annually . As this is a live vaccine, it will be inactivated by antibiotic given within 7 days of vaccination. Correct vaccination will normally prevent outbreaks. When outbreaks do occur all at risk livestock should be treated with a long acting antibiotic to stop possible early infections. Then they should be vaccinated 7 to 10 days later. If any animals become sick, retreat  them immediately and vaccinate again after a month. Do not use vaccines and antibiotics simultaneously.
    Notify the nearest state veterinarian as anthrax is a notifiable disease. Move animals to a clean camp, away from where any anthrax carcases have contaminated the soil. Cremate preferably or bury deeply all dead animals and in contact materials. Do not allow animals off the farm for 2 weeks after vaccination or 6 weeks if going to slaughter.  Clean all animal facilities and equipment.  Use insect repellents. Control scavengers. Ensure that people who handle sick animals use proper sanitary procedures.  It is often not achievable to decontaminate soil, but if a small area was affected, removal and burial of topsoil with formaldehyde treatment of the exposed surface may be successful.
    Remember that anthrax is a zoonosis which can infect animals as well as humans. If anyone was exposed to possible infection without proper protection, get medical advice without delay.

Dr Joan Kleynhans-Jordaan is ’n ervare veearts en het tydens haar loopbaan wat reeds oor vier dekades strek, met plaasdiere, huisdiere en wild gewerk. Sy doen tans lokums in die Wes-Kaap en elders en skryf graag oor haar wedervaringe. Sy is ook ’n ywerige fotograaf en kunstenaar. Sy skilder veral graag kleurvolle hondeportrette.