With new tick-borne diseases emerging and expanding their ranges, there's more reasons than ever to tuck your pants into your socks if you're on a hike.
At the annual meeting of the American Society and Tropical Medicine and Hygiene, Yale University researchers presented work on babesiosis, a malaria-like disease spread by a parasite that attacks red blood cells. The deer tick, which also spreads Lyme disease, is the most common vector for the babesiosis parasite, Babesia microti.
The research suggests that babesiosis is on the rise. From 2000 to 2008, the number of cases of the condition rose from about 3 per year to around 100 per year, and the disease expanded from 30 to 85 towns in Connecticut. On Nantucket Island, about 10 percent of deer ticks carry the B. microti parasite, according to Yale researcher Maria Diuk-Wasser.
Babesiosis has also increased its foothold in the Lower Hudson Valley of New York, jumping from 6 cases to 119 cases per year between 2001 and 2008.
Diuk-Wasser and colleagues have also investigated how the Lyme disease parasite can give a boost to the babesiosis parasite. The researchers infected mice with either one of the parasites, or both at the same time, then allowed ticks to feed on the mice. The ticks that fed on mice infected with both parasites were more likely to be carrying B. microti, and tended to carry higher concentrations of it, than ticks that bit mice just infected with the babesiosis parasite.
"This suggests that Lyme disease is somehow intensifying transmission of babesiosis," Yale researcher Peter Krause said in a statement Monday.
Babesiosis isn't the only rising star amongst tick-borne diseases. The deer tick virus, carried by the hard-bodied deer tick, was not considered a threat until 2001, when traces of the virus were found in the brain of a man that died from a mysterious encephalitis infection.
At the same meeting of the ASTMH, New York Medical College researcher Marc El Khoury reported that many cases previously attributed to Powassan virus are actually more likely caused by the deer tick virus.
What's more, deer tick virus is on the rise. While only 40 cases attributed to Powassan virus were reported in the U.S. and Canada between 1958 and 2003, 33 cases were reported in Wisconsin, Minnesota and New York in the four-year period between 2008 and 2012.
"Almost all of these cases are in Lyme country, where humans are much more likely to be preyed upon by deer ticks carrying deer tick virus than ticks carrying Powassan virus," El Khoury said in a statement Monday. "Now it appears that in Lyme-endemic areas, people can not only get Lyme disease or babesiosis, but also a deer tick virus-related meningoencephalitis."
While many of these infections are mild, severe deer tick virus infections can lead to brain inflammation, which causes permanent brain or nerve damage in about half of patients and has a fatality rate of around 15 percent.
Deer ticks can also carry the bacteria that causes human granulocytic anaplasmosis, which attacks the white blood cells of the immune system. Cases of HGA have risen in North America and Europe, and the disease is now cropping up in Asia, Johns Hopkins University School of Medicine researcher J. Stephen Dumler reported at the ASTMH meeting.
Plus, hundreds of cases of presumed HGA in China turned out to be caused by a new tick-borne virus with a 30 percent fatality rate.
This past August, CDC researchers wrote in the New England Journal of Medicine about another newly discovered tick-borne virus that infected two farmers in Missouri this past summer. Scientists know that this particular bug is a phlebovirus, a family that also includes the mouse-spread hantavirus.
"We increasingly need to apply the most sophisticated genetic tools to identify the numerous new tick-borne microbes that have the theoretical capacity to infect humans," Tufts University researcher Sam Telford said Monday. "Only by raising awareness among health professionals of what to look for, publishing case reports with good laboratory details, and doing good epidemiology will we be able to truly understand and appropriately respond to emerging disease threats."