Babesiosis: yet another disease spread by deer ticks

Based on the work of Dr Peter J Krause M.D., Connecticut Children’s Medical Center, Hartford and University of Connecticut School of Medicine

“With such extensive human exposure to ticks and a relatively large number of Lyme disease cases in Fairfield County, and considering recent trends, the number of cases of babesiosis is likely to increase appreciably in the future.” Centers for Disease Control and Prevention 2004 

Deer ticks spread more than Lyme disease. Two other increasingly common diseases are causing serious illness in humans and sometimes death in Fairfield County towns, babesiosis and ehrlichiosis. All three diseases are spread by the bite of the same black legged ticks that feed on white tailed deer and some patients can become infected with more than one organism at one time.

Babesiosis, an infection caused by a parasite that invades and lives within red blood cells like malaria, is a newly recognized disease in humans until recently only seen in wild and domestic animals such as cattle. It was first recognized in humans in 1957 when a young cattle farmer with no spleen died from the disease in Croatia. The first human case in the US was recognized on Nantucket Island  in 1968. Approximately 1000 cases of babesiosis have been reported in Connecticut alone between 1991 and 2007 (see graph.) 
Fairfield County is one of the high risk area: the Centers for Disease Control and Prevention issued a warning for this area in 2004. A man from Redding was seriously ill in intensive care with babesiosis last summer and a 77 year old man from Wilton died from complications of babesiosis in August. Many other reported cases occur during the summer months along the immediate coast and off-shore islands of the Northeast, such as Nantucket, Block Island and Shelter Island where deer and the deer (black legged) tick are common. 


Babesiosis cases in Connecticut 1991-2007

How is babesiosis spread?
 The deer is essential for the successful spread of the tick that carries babesiosis as it allows the tick to breed and amplify its numbers. The adult female tick needs the protein from a 5 to 7 day feeding on deer blood to successfully lay its 2000 eggs. The growth of the deer population over the past few decades is thought to be the major cause for the dramatic increase in human cases of both Lyme disease and babesiosis. In turn this growth in the deer population is due to the loss of the deer’s natural predators and to the regrowth of woodlands in the northeastern US when farms were abandoned in the early 1900s, aided by the diminishing number of deer hunters.
Babesiosis is thought to have spread more slowly through the northeastern US than Lyme disease when deer and their ticks re-colonized the state from a pocket off the southern New England coast. This probably is because babesiosis, unlike Lyme disease, is not also spread by birds.
Who gets babesiosis?
 People who spend time outdoors in tick infested areas are at an increased risk of exposure. The disease is more severe in people over age 50 and in people who have weakened immune systems, especially those who have had their spleens removed or who have certain types of cancer. It also affects young people and is more common in children than currently reported. Unlike Lyme disease, babesiosis has no diagnostic rash so signs and symptoms are easily mistaken for a viral illness. In coastal New England the number of cases is in the category of “moderately common”, similar in incidence to gonorrhea, with evidence that it is increasing relative to Lyme cases.
Symptoms Not all people will become sick if they have babesiosis, but most will, usually within 1-6 weeks of the tick bite.. The illness can range from very mild to very severe and even fatal in 5% of cases. Patients may experience fever, drenching sweats, muscle or joint pain and malaise. A breakdown of the red blood cells, called hemolytic anemia, is also common. Less frequent symptoms include nausea, vomiting, headache. Patients who have a simultaneous infection with Lyme Borrelia experience a more severe acute illness.
Diagnosis
 Babesiosis can be diagnosed by blood tests, looking for an immune response to the parasite and examining smears of several 100 red blood cells and recognizing the characteristic "ring" form taken by the Babesia parasite within the red blood cells of the patient. All babesiosis cases must be reported to the Connecticut DPH.
Treatment Some people do not become sick enough with babesiosis to require treatment, but a number do. Effective therapies are usually a combination of two antibiotics. Up to 38% of patients over 50 yrs of age require hospital admission for treatment. 
Preventive measures consist of personal (protection and tick checks), residential, and community approaches. The use of multiple strategies is most likely to be effective, just as for Lyme disease.
Community efforts to reduce the density of deer can sharply reduce the risk of infection. This is potentially the most successful preventive measure. Deer were reduced to around 6 deer per sq mile in Great Island, a peninsula on Cape Cod, Massachusetts and within 3 to 5 years the density of deer ticks fell precipitously. Only one case of babesiosis has been reported from that site in the 20 years since deer reduction. People with a history of babesiosis are prohibited from donating blood.
Public awareness: A study is currently underway to examine the number of ticks collected from public recreation and school locations in Fairfield County towns that carry the babesiosis parasite. A study was recently completed that showed a 60% infection rate with Lyme bacteria, an unexpectedly high rate of infection of ticks.

This article is based on information from the Connecticut Department of Public Health, the Centers for Disease Control and Prevention and the work of Dr Peter J. Krause, M.D., Division of Infectious Diseases, Connecticut Children’s Medical Center, Hartford and University of Connecticut School of Medicine. See: Human Babesiosis, Vannier, Gewurz, Krause: Infectious Disease Clinics of North America, 22, (2008) 469-488.