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Pursuing a pathogen: building on a century of research

A cow standing in a pasture.
Anaplasma marginale is transmitted through a tick’s salivary glands and into a cow when it feeds.

In 1908, using just a microscope, veterinarian Sir Arnold Theiler discovered a microorganism inside the gut of ticks that sickens thousands of cows annually.

More than a century later, researchers at Washington State University’s College of Veterinary Medicine and the University of Pretoria in South Africa are using molecular tools to build on Theiler’s work.

“It took more than 100 years but we are inching closer toward what has always been the goal — a safe, global vaccine that is effective against all strains of the pathogen,” said Professor Kelly Brayton, a researcher in WSU’s Veterinary Microbiology and Pathology department.

The pathogen, Anaplasma marginale, is transmitted through the tick’s salivary glands and into the host when ticks feed.

The bacteria makes its way into the bloodstream and infects red blood cells, causing anemia, fever, breathlessness, weight loss, lethargy, abortion and death. The infection is known as Bovine Anaplasmosis and if left untreated, cattle can experience up to a 36% mortality rate.

“This is one of the top three widespread livestock diseases in the world,” Brayton said. “In addition to sickness and death, this disease can spread quickly and result in major economic losses for beef producers.”

Brayton and the team’s goal is to produce a vaccine that can be used against the diverse strains of Anaplasma marginale in the United States and worldwide.

Currently, a blood-based vaccine developed by Theiler is still in use in South Africa, but it does not provide complete protection against Anaplasma marginale. It can’t be used in the United States because the vaccine can also transmit other blood-borne pathogens.

Closeup of Kelly Brayton
Kelly Brayton, a researcher in WSU’s Veterinary Microbiology and Pathology department.

According to research in Ticks and Tick-borne diseases, five of Anaplasma marginale’s outer proteins have been identified as potential targets for a global vaccine.

For several years the five proteins — Am779, Am854, omp7, omp8 and omp9 — have been identified as potential vaccine targets in the United States due to their location and function.  What remained unknown is if the proteins’ vaccine candidacy would remain valid across the diverse strains of Anaplasma marginale in endemic regions like South Africa.

“If you’re trying to develop a vaccine you want it to work everywhere. Based on our research, a vaccine targeting these five proteins should be just as effective in the United States as it is in South Africa,” Brayton said.

To conduct the research, Brayton and her colleagues at the University of Pretoria collected a wide variety of Anaplasma marginale strains from throughout South Africa.

Once collected, researchers cloned the candidate genes from the South African strains and compared the potential target proteins with the versions for the United States.

“The proteins weren’t particularly diverse, which is one reason why they are on our list to serve as good vaccine candidates,” Brayton said.

The research is just the latest publication coming out of the WSU-University of Pretoria partnership formed by Brayton and her colleagues in 2012.

A $625,000 grant recently awarded by the National Institutes of Health will now allow WSU and University of Pretoria to collect epidemiological data on tick-borne diseases in South Africa for the next four years. Brayton has partnered with University of Pretoria Professors Nicola Collins and Marinda Oosthuizen on the project.

The team works with the Mnisi people, a community of subsistence farmers, to test ticks and blood from humans, captured rodents, community dogs and livestock.

“Malaria in Africa has declined over the past 10 to 15 years but the incidence of acute febrile illness has not. Our premise is that some of that acute febrile illness is due to tick-borne disease,” Brayton said. “There’s also this question: Are new disease agents emerging? This grant will also look for those pathogens.”

A nurse from the National Center for Infectious Diseases will staff a clinic in the community to screen people experiencing acute febrile illness. All patients are asked to take part in the study and provide blood samples and answer a questionnaire.

University of Pretoria has a long-standing relationship with the Mnisi community: over 80 research projects are run in the community. In exchange, UP veterinary students provide free veterinary care through a clinical rotation in the community.

“Ticks are spreading, and they are gaining new ecological niches in areas so the diseases that go with them are spreading and becoming more of a problem,” Brayton said. “This partnership and program will help us keep a pulse on tick-borne disease and detect new diseases early.”

Media contact:

  • Kelly Brayton, WSU College of Veterinary Medicine, 509-335-6340,

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