As the world marks tuberculosis (TB) day tomorrow, one of the things animal health specialists will be discussing is how to curb the spread of the disease from animals to human.
Bovine TB, which affects animals, remains a serious threat to livestock and human health.
The World Organisation for Animal Health (WOAH) notes that the chronic respiratory disease is caused by a bacteria called Mycobacterium bovis (M. bovis), which is closely related to the bacteria that causes human tuberculosis (M. tuberculosis)
Bovine TB is a zoonotic disease, which means that it can be naturally transmitted between animals and humans.
However, it is more serious and harder to treat than human tuberculosis. This is because the bacteria is resistant to the antibiotic pyrazinamide used to treat human TB.
Dr Joseph Mugachia, a veterinarian at the Garden Veterinary Services in Nairobi, says Bovine TB is an infectious disease among cattle and affects other domesticated animals, and certain wildlife populations.
It causes persistent coughing, bleeding through the nose or mouth, nodules of the skin and udder (at advance stage of illness) and eventually death.
He says that the infectious Bovine TB is not treatable in cows. “TB is a neglected disease whose diagnosis and control is not given much attention. The emphasis is only at the slaughterhouse when checking the safety of meat for consumption,” says Dr Mugachia.
He adds that the disease is not treatable because the risk analysis on cost, time and spread shows that it is not practicable to treat.
“It is too expensive because cows have bigger mass than human hence need more drugs. It takes too long to treat, which increases the risk of transmission to humans and other animals. The best thing, therefore, is to destroy the affected animals.”
INHALING DROPLETS FROM COUGHS OR SNEEZES
In dogs and cats, Dr Mugachia says skin reaction test and X-rays are used to detect the disease. “In cattle, we use only the skin reaction test. The reason being X-ray is logistical difficulty in cattle due to large body mass which is poorly penetrable by the rays.”
Animals too can get infected with human TB and that chicken TB can also affect both cows and humans and vice versa, he offers.
Dr Dave Muthama, who deals with human TB at the Elizabeth Glaser Pediatric AIDS Foundation, says that Bovine TB in human is treatable, just like the ordinary type, through a combination of antibiotics that kill the Mycobacterium bovis bacteria.
However, one complication is that M. bovis is always resistant to the TB drug pyrazinamide, although other first line TB drugs can still be used.
And like the human disease, Bovine TB is spread through inhaling tiny droplets from the coughs or sneezes of an infected animal or person and through contaminated food, making it gradually a greater threat to human health than previously thought.
It mainly affects the lungs, but it can also affect any part of the body, including the abdominal glands, bones and nervous system.
In human, its symptoms include fever, night sweats, persistent cough, diarrhoea, weight loss and abdominal pain.
According to the World Health Organisation (WHO), of the things that makes it difficult to know how much human disease is caused by M. bovis is because most commonly used laboratory processes can’t distinguish between M. bovis and M. tuberculosis.
The organisation further notes that the true burden of zoonotic TB is likely to be underestimated due to lack of routine surveillance data from most countries.
Dr Muthama, however, says that with advance in technology, it is possible to detect the rare forms of TB using gene expert tests.
MILK SHOULD BE TESTED
“Gene expert test is like looking at the DNA of the organisms. We have found out that these rare forms of TB are in small proportion among human beings.”
In 2016, there were an estimated 147,000 new cases of zoonotic TB in people globally, and 12,500 deaths due to the disease with most developed countries recording a much smaller number of cases of TB caused by M. bovis in humans, according to WHO.
Africa is the highest hit with an incidence of 71,000 and mortality of 9,270. It is followed by South East Asia with 44,900 incidences against 2,090 deaths. Western Pacific is third with 10,000 incidences and 309 death.
In 2018, Kenya listed Bovine TB among the 36 priority zoonoses diseases to be tackled. Others were anthrax, brucellosis, avian influenza and other pandemic influenza viruses and plague.
According to Dr Mugachia, the best way to save both humans and livestock from Bovine TB is to control its spread.
“I would advise that animals in high risk areas be tested for TB. Animals should be housed with good air circulation and people who are suspected to have TB should be tested and treated as soon as possible to avoid spreading it to the livestock,” says Dr Mugachia.
High risk areas, he says, are arid and semi-arid, and places like Kiambu, Vihiga and Kisii where families live close to animals due to small acreages of land.
He adds that whenever TB is diagnosed on the farm, milk should be tested to rule out contamination.
Cattle can spread Bovine TB to other cattle directly via respiratory route, via infected milk, during birth through the placenta and contamination of grazing areas or natural water sources.