Infection rates for bovine leukosis, which can cause cancer in cattle, are growing.
“(Producers) should be worried, and they should do something about it because, as I said, the prevalence is high,” said Omid Nekouei, a PhD candidate of veterinary epidemiology at the Atlantic Veterinary College.
Nekouei, who is working on a thesis study on bovine leukosis, said he has found the number of dairy cattle with the disease has increased in the last 15 to 20 years. Bovine leukosis is a virus that can cause a form of cancer called bovine lymphosarcoma.
“The lympho site is a white blood cell in our bloodstream, and cattle have the same type of white blood cells,” said John Campbell, head of the large animal clinical sciences department at the University of Saskatchewan’s Western College of Veterinary Medicine.
“Basically this virus can cause a proliferation of those white blood cells, just like a leukemia in people.”
The proliferation can cause enlarged lymph nodes in cattle and can also occur in the heart, stomach and reproductive tract.
Cattle can have the bovine leukosis gene and never develop cancer, which is usually found only in older animals.
The disease is commonly spread through blood contamination.
“If you injected one cow and then injected another cow with one needle, you could potentially spread the virus from one animal to another,” Campbell said.
The disease can also be transmitted in the uterus of the cow to the calf and through milk from cow to calf.
Bovine leukosis is more prominent in dairy herds, which Campbell said could be because dairy cattle are sold and moved around more often than beef animals and because multiple dairy calves are fed milk from the same cow.
David Kelton, research chair in dairy cattle health at Dairy Farmers of Ontario, said the disease’s major economic effect is on trade.
“(European countries have) been very aggressive over the years at identifying diseases and especially if they’re present at a very low level in their population, that they’ve worked to get rid of them.”
Kenton believes Canada has not fought to eliminate the disease because there has been no major effect on humans or the beef and dairy industries.
However, an American study recently linked bovine leukosis to breast cancer in humans.
The study, which was explained in an article published in September called Exposure to Bovine Leukemia Virus is Associated with Breast Cancer: A Case-Control Study, found that breast cancer incidence is markedly higher in countries with raw milk consumption.
It also suggested that humans could have been introduced to the bovine leukosis gene.
“This certainly isn’t a (definitive) study, but it certainly raises the question,” Kelton said.
It’s not certain how many cows are affected with bovine leukosis in Canada, but the first national dairy study is being completed this year.