An old scourge … or an emerging problem
Anthrax is an infectious and frequently fatal disease of livestock, wildlife and even humans, and is caused by the bacterium Bacillus anthracis. Anthrax is one of the oldest diseases known to man, and the biblical fifth and sixth plagues, which first affected livestock and then humans in Pharaoh’s Egypt, were most probably due to anthrax.
From earliest historical records up until the development of an effective vaccine midway through the 20th century, anthrax was one of the foremost causes of uncontrolled mortality in cattle, goats, horses and pigs worldwide. A sharp decline in anthrax outbreaks in livestock occurred during the period 1930 to 1980, as a result of successful national vaccination programs, in many parts of the globe. More recently, however, a resurgence of this disease in livestock has been reported in some regions, where complacency and a false sense of security have derailed vaccination programs. In addition, many outbreaks of anthrax in wildlife go undetected and unreported because of inadequate surveillance and the difficulties associated with disease monitoring in free-ranging wildlife. With the increase in wildlife ranching, ecotourism and hunting in Southern Africa, surveillance for and awareness of this disease becomes even more important.
The life history of anthrax bacteria differs markedly from most other pathogenic micro-organisms in that this bacterium needs to kill its host in order to propagate itself in nature. There are two stages in the life cycle of this bacterium, the first being a highly resistant spore that can lie dormant and survive for years or even decades in the soil. Survival of these spores is optimum in alkaline soils with high calcium and organic content and these conditions are present in certain areas known as anthrax endemic areas. In sub-Saharan Africa, these anthrax endemic areas include the Kruger National Park and Northern Cape Province in South Africa, Etosha National Park and the Caprivi strip in Namibia, Chobe National Park in Botswana, Hwange and Gonarezhou National Parks in Zimbabwe, Luangwa National Park in Zambia, Queen Elizabeth National Park and Lake Mburo National Park in Uganda and Lake Manyara National Park in Tanzania. The second stage of the bacterium’s life cycle occurs when the spore enters an animal’s body and germinates to form a bacillus, which then undergoes rapid multiplication in the bloodstream, and causes acute death within a few days. If the carcass is then opened, those millions of anthrax bacilli will form spores and go back into the soil.
Anthrax can infect most warm-blooded animals, but herbivorous animals are more susceptible than carnivores or primates. Most herbivorous animals become infected by ingesting contaminated water or vegetation. They may also become infected if bitten by biting flies that have recently fed on an infected animal. Infected animal carcasses (old or fresh) are the cause of contamination of soil and grazing, and spore-ladened water run-off after rain storms may result in spore accumulation in lower-lying water pools. In addition, animals in the terminal stages of anthrax are frequently dehydrated and are running high body temperatures. They seek out and remain close to water points because they are very thirsty, and they may die close to the water or even in the water, resulting in serious contamination. Blowflies (brommers) that feed on carcass fluids may also contaminate vegetation (especially browse) in the immediate vicinity of a carcass and this is an important source of infection for browsing antelopes. Chewing of infected bones from old carcasses (usually in phosphate deficient areas) by pregnant or lactating females is a common source of infection. Mammalian predators that feed on infected carcasses may become infected, but the disease is less acute, and infected lions and leopards frequently develop massively swollen heads, faces and lips. Some die and some recover and are then immune. Cheetahs are very susceptible and die acutely, but hyenas and vultures are highly resistant. In addition, scavenging birds that feed on infected carcasses may transport the infection over long distances on their beaks, feet and feathers. Ostriches are the only birds in which anthrax deaths have been reported.
In the lowveld and bushveld areas of our country, anthrax outbreaks are generally a winter / dry season phenomenon, whereas in the Northern Cape (where certain biting flies appear to be important transmitters) late summer outbreaks are more frequent. Although most mammals are susceptible to anthrax, in South Africa, kudu, buffalo, waterbuck, zebra, nyala, roan antelope and elephant are most commonly affected. Anthrax should be suspected when sudden deaths are observed, frequently in a cluster, and may involve several wildlife species. The victims are generally in good body condition, and dark, unclotted blood is frequently seen exuding from one or more body openings. Red / purple spots (skin haemorrhages) may be seen in hairless areas on the inside of the thighs, udder and genitals.
ACTIONS IF YOU SUSPECT ANTHRAX – A FEW DO’S AND DON’T’S
Firstly – DO NOT CUT OPEN THE CARCASS! Opening the carcass will generate millions of spores, and unprotected handling of the animal tissues will place you and your helpers at risk of developing anthrax.
Secondly – attempt to cover up the carcass with branches or plastic sheeting, and call for veterinary assistance to confirm the diagnosis. Then increase the surveillance on your farm / ranch / game reserve, and GPS and cover all carcasses found. If available, microlites and helicopters are very useful for finding carcasses. Covering the carcasses denies access to scavenging birds, blowflies and biting flies, and unopened, covered carcasses will develop fewer spores and decompose rapidly, which destroys large numbers of anthrax bacilli in the carcass. Covering will, however, not deter mammalian scavengers, such as jackals or hyenas. Once the diagnosis has been confirmed, it is important to report the outbreak to the nearest state veterinary office (anthrax is a notifiable and controlled disease). The infected farm will then be placed under quarantine, while control options are instituted. One should then go back to the GPS-located carcasses, and if fuel (wood, fossil fuels or old crankcase oil) is available, one should attempt to burn as many carcasses as possible. This is the best disposal option. Other disposal options are to bury the carcasses and add agricultural lime or HTH before covering. Unfortunately, the spores from buried carcasses will at some stage reach the surface again and may cause another outbreak years later. Another option would be to uncover the carcasses that were covered with branches or plastic, spray them with 5% formalin, and then re-cover them and allow them to compost.
If the carcasses are all clustered in one ‘hotspot’ area or camp on the farm, serious consideration should be given to burning that block or camp. The fire will destroy many of the spores on the vegetation, and reduce the number of blowflies or biting flies. It will also force the animals to disperse away from the ‘hotspot’ area, and the burnt area should remain unattractive to herbivores for some time.
The cornerstone of anthrax control in livestock is vaccination. The vaccine is locally made, inexpensive and gives protection that lasts for approximately 12 months. Livestock can easily be handled using a crush, and large numbers can be vaccinated within a short period of time. Unfortunately, it is much more difficult and expensive to vaccinate wildlife. High-value species kept semi-intensively in relatively small camps may be remotely vaccinated from the ground using drop-out darts. Free-ranging wildlife are much more difficult to vaccinate, requiring vaccine darting from a helicopter, or driving herd animals into a capture corral, and then vaccinating with a pole syringe. The problems associated include high stress levels on the animals, disrupting of family groups and the need for some form of functional, robust marking system so that one knows which animals have been vaccinated. In addition, the vaccine only gives protection for one year. Better vaccines giving longer protection are currently being researched.
MOVEMENT OF ANIMALS
Translocation or movement of animals during an outbreak, from an infected farm to another property or sale yard, should only be considered after the animals have been isolated for a minimum of 14 days after they have been vaccinated. In an emergency, animals may be injected with antibiotics, moved and then vaccinated at destination 14 days later. It is important that antibiotics and vaccine are not given together because the antibiotics will kill the vaccine strain of anthrax and prevent development of immunity. These options must be carried out under state veterinary supervision.
OTHER PREVENTATIVE MEASURES
If an anthrax outbreak occurs in your area, or in the vicinity of your farm, the following measures may reduce the possibility of your farm becoming infected.
1) Make your water points unfriendly for vultures and other scavenging birds. Partially cover small water holes with branches, leaving only a few gaps for the animal to drink. Place foreign deterrent objects, which can be easily seen from the air (pieces of cloth, shiny objects or scarecrows), close to the waterhole. For larger dams, place obstruction in potential landing areas or shallow wading areas to deter bathing of avian scavengers. Running water (i.e. rivers and streams) is not a problem because of the dilution and flushing effect.
2) Short-term blowfly and biting-fly control using traps and insecticides may be considered.
3) Avoid purchasing and introductions of animals from outbreak areas, unless vaccinated or treated according to state veterinary protocol.
HUNTING, PROCESSSING OF MEAT AND TROPHIES DURING AN ANTHRAX OUTBREAK
As a general rule, hunting, processing of meat and trophies on a property that is experiencing an anthrax outbreak should be avoided. This is because of the very real risk to human health. Humans may become infected with anthrax by handling the tissues of an infected animal or eating the meat of an infected animal. There is always a chance, all be it relatively small, that a hunter may shoot an animal shortly before it dies of anthrax. In such a case, millions of anthrax organisms are already present in the tissues of this animal. Handling the tissues of this animal by the hunter, PH or field staff may result in multiple human exposures. The most common form of anthrax in humans is skin anthrax, which if neglected can be fatal. Eating undercooked meat, biltong or dry wors made from anthrax-infected animals may result in intestinal anthrax, which is even more serious and has a high mortality rate. The handling of trophies, even dried hides or skulls, is not without risk. People have become infected with anthrax after buying and using traditional African drums covered with animal skins. Where the decision is made to shoot a healthy-looking animal during an outbreak, to minimise risk, arrange for a vet or competent laboratory to examine a blood smear from the carcass. Only make biltong or wors if the blood smear is negative. Cook fresh meat well!! Trophies, such as skulls and tusks, can be soaked in 10% formalin for 48 hours to sterilise them, and dried skins require special disinfectant processing at the taxidermist. Is it really worth the risk?!
With the greater part of the life cycle of anthrax occurring as a dormant, highly resistant spore in the environment, and accepting that surveillance and monitoring for disease in free-ranging wildlife is by nature very difficult, we can expect that anthrax outbreaks in wildlife will continue to occur sporadically in high-risk endemic areas in the future. We must always be alert and any sudden unexpected deaths in wildlife should be thoroughly investigated.