The Emergence of Babesiosis

Another tick-borne disease is already endemic in Connecticut and other regions of the United States and researchers at the Yale School of Public Health have evidence that its range is still expanding.

While babesiosis is far less familiar than Lyme disease among the general public, the tick-borne illness is receiving increased attention from researchers at the Yale School of Public Health who are actively studying its expanding range and monitoring the number of new infections. In contrast to Lyme disease, babesiosis has a greater potential to be lethal and the infection can be transmitted through blood transfusion. Peter J. Krause, M.D., a senior research scientist at YSPH, has been studying babesiosis for more than 20 years and recently co-authored with Edouard Vannier, Ph.D. of Tufts Medical Center in Boston a review article in the New England Journal of Medicine that provides an overview of what is know about the disease and what remains to be learned.

Babesiosis has been classified as an “emerging health risk.” Does this mean that the threat is growing and that it will likely continue to do so?

PK: The number of cases is steadily increasing in every state in the northeastern United States where babesiosis has been reported. Cases also are being reported in other parts of the world where human babesiosis had not previously been reported.

Most everyone, especially here in Connecticut, is familiar with Lyme disease, while babesiosis remains largely unknown. Both diseases are transmitted by the same tick species but the symptoms and the potential outcomes are quite different. How so?

PK: Human babesiosis and Lyme disease are caused by different microorganisms that infect different cells and elicit different immune responses. The Lyme disease microorganism is deposited in the skin where it causes a rash. If not treated in a timely manner, it may disseminate to the joints, nervous system and heart. The Babesiamicroorganism infects red blood cells and may cause mild systemic symptoms such as fever, headache and fatigue, but also may cause severe illness in people who are immunocompromised and in those over 50 years of age in previous good health.

Babesiosis also has a greater potential to be lethal?

PK: The overall babesiosis fatality rate is 6 percent to 9 percent in hospitalized patients and may reach as high as 21 percent in people who are immunocompromised. Meanwhile, Lyme disease-associated fatalities are rare.

You have traveled internationally to examine patients who may have been ill with babesiosis. Does this mean that there are not many doctors trained to diagnose and treat this disease?

PK:Many physicians living in areas where babesiosis is endemic, such as parts of the Northeast and the upper Midwest, are well versed in the diagnosis and treatment of this disease. Physicians practicing where only a few cases have been described generally are not familiar with babesiosis.

The geographical spread of babesiosis in the United States is not as great at Lyme disease. Based on what you have seen, is the range of babesiosis likely to grow in the coming years?

PK: Dr. Maria Diuk-Wasser and Dr. Durland Fish, both of the Yale School of Public Health, and I are currently writing a paper that describes the spread of babesiosis into areas in Connecticut where only Lyme disease was previously identified. Other investigators are observing the emergence of human babesiosis in other areas of the United States such as in Maine, Delaware, Maryland and California and other parts of the world including Australia and Europe.

How does babesiosis compare at this point to Lyme in terms of new infections? Is the gap narrowing?

PK: We previously established that the incidence of babesiosis is close to that of Lyme disease on Block Island and southeastern Connecticut whereas the ratio of Lyme disease to babesiosis cases is about 25 to 1 nationally. We believe that the gap between the number of cases of babesiosis and Lyme disease in the United States will narrow over the next decade.

Why do some ticks carry the bacterium responsible for Lyme and others the parasite for babesiosis if the ticks are living and breeding in the same areas?

PK: Ticks acquire the microorganisms that cause babesiosis or Lyme disease from field mice. Some mice are infected with the Lyme agent, some with the Babesia agent and some with both.

Can a single tick carry each microorganism and simultaneously and potentially infect a person with both?

PK: Field mice and ticks can carry both microorganisms simultaneously and some ticks transmit both to humans who then become simultaneously infected.

Are there other tick-related diseases on the horizon that are cause for concern?

PK: Dr. Fish discovered an organism called Borrelia miyamotoiin deer ticks in Connecticut. It is closely related to the Lyme microorganism but causes relapsing fever. He and I described the first human cases of infection with Borrelia miyamotoiin collaboration with Russian researchers, as the cases occurred in Russia. We are now looking for evidence of this infection in people in the United States. Another cause for concern is the deer tick virus that can cause brain infection. Currently, there are only a few cases in the northeast each year.

Were many people talking about babesiosis 20 years ago?

PK: A small group of people in southern New England and New York were aware of this disease but it was largely unknown 20 years ago when I began babesiosis research. Many more people are now aware of babesiosis, as the number of tick-borne cases and blood transfusion cases have increased. Babesia microti is currently the most common blood transfusion-transmitted pathogen reported to the Food and Drug Administration (FDA) in the United States. Although the actual risk of acquiring babesiosis through blood transfusion is low, the FDA, National Institutes of Health, Centers for Disease Control and Prevention and the American Association of Blood Banks are all supporting research to develop methods to eliminate the problem.

Babesiosis is particularly pronounced in pockets in the Northeast and along the New England coastline. Is Connecticut considered “ground zero?”

PK: Nantucket is considered “ground zero” for babesiosis in the United States because the first case in a healthy person was described there in 1969 and Nantucket was the first known endemic area where many cases were reported each year. The southern New England coastline was one of the first regions where human babesiosis became endemic.

You do a lot of your research on Block Island and Nantucket. Describe your work there.

PK: We have been carrying out babesiosis research on Block Island since 1990 when the late Dr. Andrew Spielman and I were invited to help control the disease there. Work on Nantucket began even earlier. The research at these sites now continues with Dr. Diuk-Wasser, Dr. Fish, Dr. Vannier and Dr. Choukri Ben Mamoun, Dr. Linda Bockenstedt and Dr. Erol Fikrig at the Yale School of Medicine. We are studying ticks, mice, deer and humans for babesiosis and other tick-borne diseases. It is very exciting and productive research. Block Island and Nantucket are ideal natural research study sites because they are highly endemic for babesiosis and Lyme disease, isolated from the mainland and have relatively small size and small indigenous populations that help control research variables.

Other research collaborators include Dr. Sahar Usmani-Brown at the Yale School of Public Health; Dr. Timothy Lepore on Nantucket; Dr. Janice Miller, Elizabeth Dyer and Linda Closter on Block Island; Dr. Kenneth Dardick in Storrs, Connecticut; Dr. Robert Smith in Portland, Maine; Dr. Sam Telford at the Tufts University School of Veterinary Medicine, and Dr. David Pombo in Hyannis, Massachusetts. Funding for babesiosis research has come from The Gordon and Llura Gund Foundation and the National Institutes of Health.