Date: Fri 17 Jan 2020
Source: The Herald [edited]
At least 177 cattle have died from anthrax while 87 people were treated for the disease in various clinics and hospitals after eating meat from cattle that died from the infection during this season. Anthrax is a bacterial disease that affects a wide range of animals and human beings.
Livestock, particularly cattle, take up anthrax bacteria during grazing, while people get infected when they handle or eat anthrax-infected meat. Anthrax disease occurs throughout the year, but in Zimbabwe, most cases start from onset of rainy season. It is rare to see an animal showing signs of the disease; animals are often found dead. [Actually once it gets started, ranchers will start seeing sick animals; watching more carefully, longer incubation periods. - ProMED Mod.MHJ]
Division of Veterinary Field Services, Acting Director, Dr. Wilmot Chikurunhe has told The Herald that anthrax outbreaks have been recorded in Gokwe, Nkayi, Gutu, Bikita, Marondera, Mazowe, Chegutu, Makonde and Sanyati. He said the disease is being detected in traditional outbreak areas and not affecting the whole district as it may seem from information circulating. "Even in the affected dip tanks, the disease is restricted to certain areas, although the vaccination coverage is then extended to a wider area to contain the outbreak.
"Cattle owners in anthrax areas need to ensure that their cattle are vaccinated against the disease once a year before the rainy season starts. The Department of Veterinary Services comes in to prevent massive outbreaks, but the primary responsibility for disease prevention lies with the owner," he said.
Dr. Chikurunhe said anthrax carcasses must be disposed of safely in a manner that does not leave the bacteria exposed to air. "The best method is to burn the carcasses in a pit, then bury the ashes. However, some parts of the country have firewood problems. In these areas it is recommended to dig a pit 6 feet [1.8 m] deep, bury the carcass, cover the carcass completely with soil and apply a layer of agricultural lime before filling the rest of the pit with soil. This is best done under supervision of veterinary personnel," said Dr. Chikurunhe. [Byline: Elita Chikwati]
[For maps clearly showing the locations of the individual provinces, go to <https://en.wikipedia.org/wiki/Provinces_of_Zimbabwe
>. The districts mentioned are in the following provinces: Bikita (Masvingo), Chegutu (Masonaland West), Gotwe (Midlands), Gutu (Masvingo), Makonde (Masonaland West), Marondera (Masonaland East), Mazowe (Masonaland Central), Nkayi (Matabeleland North), and Sanyati (Masonaland West).
The survival of anthrax spores is location dependent, and this facilitates mapping where the disease might be found and where control should be centered. For some relevant maps, see:
1. Carlson CJ, Kracalik IT, Ross N, et al. The global distribution of _Bacillus anthracis_ and associated anthrax risk to humans, livestock, and wildlife. Nat Microbiol 2019;4:1337-43. doi:10.1038/s41564-019-0435-4
2. Blackburn JK, Odugbo MO, Van Ert M, et al. _Bacillus anthracis_ diversity and geographic potential across Nigeria, Cameroon and Chad: further support of a novel West African lineage. PLOS Negl Trop Dis
As Dr. Wilmot Chikurunhe comments, while vaccination should center on these enzootic areas, one should extend the vaccination cover outwards because of the risk from female biting tabanid flies with contaminated mouthparts and non-reporting neighbours. Annual vaccination prior to the anthrax season protects the livestock at a minimal cost, as Sterne vaccine is extraordinarily cheap. And eradication follows from successful control. Country after country, province after province are realising the truth of this. I just wish the ranchers would be as enthusiastic. It is the procrastinators' livestock that come down, demonstrating a local persistence of risk. Experience shows that once you have gone 8-10 years without outbreaks, you can step back to just high awareness of unexpected deaths (for checking).
The spores have a reputation for "immortality", which is exaggerated. Archived spores have a 3% annual mortality. On my 1st field investigation of this disease, Max Sterne told me that in his experience the contaminated soil will present a risk for 3 months to 3 years; we repeatedly sampled the bloody soil site at that outbreak and found no live spores after 90 days, but we might have just run out of contaminated soil thanks to the repeated sampling. A study by one of my students showed the spore count decreasing by 30% per year. But in general this is an aspect of the epidemiology of this disease that is understudied. And another aspect is that over 5 to 6 years the spores in the soil lose their plasmids and become apathogenic.
The genetics of spore survival depend on a matching of the strain with the soil, Darwin again.
See: Mullins JC, Garofolo G, Van Ert M, et al. Ecological niche modeling of _Bacillus anthracis_ on three continents: evidence for genetic-ecological divergence? PLoS One 2013;8:e72451. <https://doi.org/10.1371/journal.pone.0072451
Remember, graduate students need fresh air and mud on their boots. - ProMED Mod.MHJ]