A deadly parasite in cattle may initially infect animals with multiple strains of the disease Bovine Anaplasmosis at the same time, according to a study led by Washington State University researchers.
The finding could inform new control strategies for a disease that causes serious health problems for cattle and economic problems for the beef industry that depends upon them.
“Controlling this disease is fundamental in reducing its impact on animal health, food, livelihoods and economies. These smallholder cattle farmers should be making profits, not taking losses,” said Roberta Koku, a WSU graduate student who led the study.
The study, conducted in Ghana and led by researchers at the WSU College of Veterinary Medicine, was recently published in the Journal of Infectious Diseases and Immunity.
Bovine Anaplasmosis is a major obstacle to profitable beef production. According to the latest estimates from 2012 provided by the United States Department of Agriculture, the disease costs the United States beef industry more than about $300 million per year. However, the economic impact of tickborne infections is difficult to track and has likely never been accurately measured.
The disease occurs in tropical and subtropical regions worldwide. It is spread when the parasite, Anaplasma marginale, is transmitted through the salivary glands of a tick into the host animal when the tick feeds. The bacteria enter the bloodstream and infect red blood cells.
Once an animal is infected, the disease can cause anemia, fever, weight loss, lethargy and death.
While some animals don’t show signs of disease, outbreaks can result in unexpected deaths of any number of animals in a herd. For more than 100 years, scientists have strived to produce an effective vaccine that can be used against the diverse strains of the parasite worldwide.
A blood-based vaccine is in use in South Africa but does not provide complete protection. It is also not effective against strains of the disease in other parts of the world.
For Koku, a Ghana native who is part of WSU associate professor Susan Noh’s laboratory, the work is especially critical, not just for the animals but to alleviate the intervention costs for farmers in her home country, who are trying to manage the disease with antibiotics. In addition, she said the antibiotic use also drives the threat of antibiotic resistance.
In Ghana, Koku and fellow researchers from the Paul G. Allen School for Global Health, the USDA and WSU’s Veterinary Microbiology and Pathology research unit monitored 16 uninfected animals that were introduced into an endemic herd where 97% of animals were infected with multiple strains.
Blood samples were collected daily to document any infection. It didn’t take long before all 16 introduced animals were infected with at least two strains of the parasite. Most animals were infected with three or four strains, and researchers noted as many as six strains in an animal.
The scientists also noted the number of strains entering a host animal after an immune response was 16% lower than those strains present before an immune response.
Koku said understanding the number of strains initially infecting the animal and at which particular timepoint is key.
Knowing fewer strains enter a host after an immune response and understanding how strains come about will allow Koku and her colleagues to zero-in on those strains associated with severe disease.
Now, the team plans to take those strains and closely examine their genetic makeup.
“This genetic portion of the work is in the early stages, but it will give us an idea of what is happening during an infection and could give us some ideas for intervention,” she said.