Searching for blood once again this season: tick, tick, tick

With luck, the fierce winter killed a lot of ticks, but let’s not count on annihilation. This is the time of year when the female of Ixodes scapularis, also called the black-legged or deer tick, lay eggs. In July and August, these eggs hatch into larvae, which search for passing warm-blooded animals (usually mice). 

After a blood meal, the larvae drop off the host and transform into nymphs — bizarrely, nymphs gain a pair of legs and have eight to the larva’s six. The nymphs survive through the fall and winter and search for a host in May, June and July. They attach to a leaf or blade of grass with their two new legs and wave the front six in the air until they grasp a mouse, squirrel or bird; inserting a fierce file-looking mouth part through the surface layer of skin and into the dermis, they start to suck blood. Some of the tick fluids escape into the host, transmitting disease. 

Each tick stage — nymph, larva and adult — requires a blood meal. Nothing happens in the tick’s world without an animal’s blood to feed the next step in the life cycle. Ticks are arthropods, but not insects. They don’t have inactive winter stages like insects and can spring into action on a warm day, even in winter. 

Ticks can transmit diseases caused by viruses, bacteria or complex protozoan cells. Let’s worry only about the infections that occur in New England. The most common is Lyme disease, first described in 1975 in a group of arthritis patients in Lyme, Conn. It is caused by the bacterium Borrelia burgdorferi. Cases of Lyme disease in Connecticut peak in July, producing thousand of infections per year; infections may be under-reported. B. burgdorferi divides rapidly at the site of the bite, forming a bulls-eye rash about 60 to 70 percent of the time and then disseminates to skin, heart, joint and nervous tissues where serious inflammation occurs as the immune system mobilizes to kill the bacteria. Treatment with antibiotics limits the damage. There is no human vaccine, but there is one for dogs. 

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Ticks carry other diseases and in our region, notably in southwestern Massachusetts, southeastern Connecticut and Long Island. Babesia microti is transmitted by ticks and causes Babesiosis, a malaria-like illness. B. microti is a protozoan and is harbored by the white-footed mouse — one study reported over 40 percent of these wild mice carry B. microti. The deer tick transmits B. microti to humans where it lodges in red-blood cells. Its life cycle resembles that of malaria. The symptoms can be mild to very serious. 

Powassan virus, which is rare, has recently been detected in ticks in Connecticut. As far as I know, there are no patients. There have been fewer than a score of cases over the last decade, but like many virus infections, when it does occur there is no treatment other than managing the symptoms.

I have spared readers many other tick-borne diseases: granulocytic anaplasmosis, Colorado tick fever, Ehrichiosis, Southern Tick Associated rash illness, Rocky Mountain Spotted Fever, Relapsing Fever, Tularemia and a strange tick paralysis disease, but you can read about them in a comprehensive summary prepared by Dr. Kirby C. Stafford, chief entomologist of The Connecticut Agricultural Research Station and available from their website (www.ct.gov/caes). Dr. Stafford also discusses preventive measures, some of which I knew about and some of which were new. 

What of the future? Jacob Lemieux, MD, Ph.D., and a Millerton resident, is studying tick-borne diseases with Pardis Sabeti, MD, Ph.D., at the Broad Institute in Cambridge, Mass. As in other areas of biology, the ability to sequence and analyze DNA quickly and cheaply can be applied to ticks. Sequencing can be used to ask what dangerous organisms ticks are carrying, how fast they are spreading in the tick population, who has been infected and perhaps, someday, how to control tick populations. The basic technique is this: At times of the year when larvae, nymphs or adults are seeking a blood meal, one drags a piece of white flannel attached to a stick across the edge of a lawn. Ticks will leap at it and then can be picked off and dropped into alcohol, which kills them and preserves their DNA and the DNA of the bacteria, protozoans or viruses that they carry. In the laboratory, the DNA of individual ticks is extracted and sequenced, which tells us what potential dangers they harbor. 

Perhaps Dr. Lemieux and his colleagues will find organisms that we did not know about, which is always a good idea. As for me, enough of sitting behind a computer, I’m ready to hunt ticks.

Richard Kessin, Ph.D., is professor of pathology and cell biology at Columbia University (rhk2@columbia.edu).