Herd(er) immunity: Anthrax vaccine blunts seasonal outbreak

LAST November, thunder clouds gathered over Mazowe, 40 km from Zimbabwe's capital, Harare, signalling the onset of the rains.

The first drops, overdue and longawaited, soon soaked into thirsty earth, but Tedious Murape (42) lay anxious in his bed.

His mind was on his livestock, particularly his cattle — a crucial repository, for the herder, of both personal wealth and social prestige.

"The rain season is a welcome season for everyone, including animals, because our existence as famers largely depends on a good season, but it also brings forth diseases, which may be harmful to the animals we depend on for our daily sustenance," Murape explained.

He was thinking of anthrax, a zoonotic bacterial disease endemic to Mazowe, which would cause more than 1 100 spillover cases in humans in five countries across southern and eastern Africa in 2023.

"For years now, in Mazowe, we have known that we are one of the country's anthrax hotspots. As farmers, we are urged to report any signs and symptoms of the disease immediately to veterinary officials, but the rain season is always a difficult period," said Murape.

These rains, arriving after a prolonged heatwave on land left sparsely covered with grazing, brought to mind the late rains of 2020, which had preceded an anthrax outbreak that killed 177 cattle and infected 87 people countrywide.

By December, Murape's fears turned to reality when he heard reports of a new outbreak in a radio news bulletin.

Anthrax, a soil-borne disease caused by the bacterium Bacillus anthracis, usually affects wild and domestic herbivores, which ingest the bacterial spores from the ground while grazing. Humans can contract the deadly infection from handling sick animals or eating their meat.

Anthrax symptoms in humans can include fever and chills, swelling of the neck or neck glands, sore throat and painful swallowing. Without treatment, anthrax can be fatal.

Reverend Spargo, the acting deputy director of veterinary field services for the Lands, Agriculture, Fisheries and Rural Development ministry told VaccinesWork that the anthrax disease is endemic in 26 known and mapped districts across Zimbabwe, including Mazowe.

"Each rain season, when the rain starts, the cattle graze close to the ground, and pick the bacteria from the soil when they graze, and only the animals which are in contact with the bacteria are affected," Dr Spargo said.

Once an area is infected, Spargo explained, the bacteria can stay in the soil for a period of about 50 years.

"It is not a contagious disease," he added, meaning that anthrax does not spread from human to human or animal to animal, "but a notifiable disease, and people must notify the veterinary services when there is a suspected case."

In December, Zimbabwe's government acquired a first volley of 426 000 vaccines to fight the disease in the identified anthrax hotspots. In total, the country requires nearly two million vaccines to control the disease.

"So far, we have vaccinated the hotspots using the vaccines that were acquired from Botswana, and we have since seen the reduction of anthrax cases after the vaccination and the campaign programme that we conduct in the hotspot areas to fight the disease," said Spargo.

Rates of infection would soon slow, but by early January, 36 animals had already died of the disease.

For subsistence farmers like Murape, the loss of a single animal is more than the loss of its dollar value of US$250– 350 .

It's also a dent in a herd, a loss of a working farm animal , and a vanished source of food and potential income.

Moreover, anthrax is not the only pathogenic threat to the grazing herds. Since 2016, Zimbabwean herdsmen have lost around 500,000 of cattle to tick-borne January Disease

(Theileriosis).

"It is always painful to lose an animal that you have invested a lot into,” Murape said.

“We have seen some people consuming the dead animals, or killing them when they are about to die, and sell the meat in a bid to get something, although they understand the dangers of doing so, they just do it out of ignorance, or desperation.”

The danger, of course, is transmission to humans.

To avoid zoonotic spillover, authorities prescribe deep burials of dead animals, or burning of the infected carcass, as even handling infected animals risks the bacterial spores entering the human body. But some people butcher infected animals to eat or sell, either in ignorance, or in hopes of softening the financial blow of a cow's death.

Still, Spargo emphasises, "It is a treatable disease. So far in 2023, we have around 532 cases of people affected with anthrax, and zero deaths."