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Tick-Borne Diseases Are Rising Sharply in Number and Variety
Most people are well aware of the dangers of Lyme disease, spread by the deer tick (otherwise known as the blacklegged tick). Many people have been educated about its severity and what to look out for, while others may have been victim to the infection themselves. The 20-30,000 people who contract it each year can tell you how its neurological symptoms can be lingering or, if untreated, permanent.
Tick-borne diseases are of particular interest and concern to scientists who are tracking their spread – and even more disturbing is the rise of these diseases over the last couple of decades. Last year the CDC warned that another disease spread by the same tick that spreads Lyme disease was on the rise both through tick bites and through blood infusions in medical centers.
Yale University researchers observed that this disease, called babesiosis, rose from 3 cases to 100 cases per year in Connecticut alone over the last 20 years. It’s rising at a similar rate in lower New York Sate, and can be found in most states along the Eastern seaboard, as well as Minnesota, Wisconsin, and even some states on the West coast. Symptoms can include fever, chills, fatigue, sweats and muscle pain; it can be fatal in 6-9% of patients, and the number is higher (about 20%) in people who contract it through blood transfusion. Researchers have likened it to malaria, since it invades and destroys the body’s red blood cells. Most cases, luckily, are treated successfully with antibiotics.
And there are other forms of tick-borne diseases whose prevalence is rising. Researchers at New York Medical College reported the rise of two “new” diseases: deer tick virus, spread by the hard-bodied deer tick, and Powassan virus (POWV), carried by the soft-bodied tick. These ticks had historically fed on groundhogs and woodchucks, but have recently been shown to affect humans as well. These viruses can range from asymptomatic to fatal in about 15% of patients. About half of the people infected with the viruses may have permanent brain or nerve damage.
Finally, deer ticks have been shown to spread human granulocytic anaplasmosis (HGA), which attacks white blood cells. This disease was originally found in North America and Europe, but has recently been seen in Asia as well. What’s perhaps even more alarming is other related species of ticks can also carry the disease, which expands its spread. Additionally, close but distinct relatives of the HGA virus have also been recorded in the US. In China an outbreak that was thought to be HGA turned out to be an even more fatal form, killing about 30% of its victims.
The experts highlight the importance of good surveillance along with, of course, good treatment. "Today's findings underscore the shifting landscape of tick-borne diseases, whose rapid emergence can challenge the best efforts of science and medicine to diagnose, treat, and prevent their occurrence," said Yale researcher, Peter Krause. For more information on tick-borne diseases, see the CDC’s webpage on the subject.
The findings of these studies were presented at the annual meeting of the American Society of Tropical Medicine and Hygiene (ASTMH).
November 14, 2012