Summertime means picnics, parties, barbeques and other outdoor activities. It also means health hazards related to these warm weather activities, including exposure to vectors such as ticks and mosquitoes. Of the many diseases spread by insects, few are actually caused by the insects themselves, but rather by other organisms such as bacteria, viruses and protozoa that are passed on when insects feed or bite. The following summarizes the more common vector-borne diseases that occur in and around the northeast.
Lyme disease is caused by bacteria that are spread by tiny, infected deer ticks. In Massachusetts, deer ticks are found everywhere, but especially in coastal areas, the islands and the Connecticut River Valley. Deer ticks cling to plants near the ground in brushy, wooded or grassy areas. The ticks climb onto and infect animals and people who brush against the plants. The tick usually must be attached for at least 24 hours to pass on the bacteria, so removing the tick promptly will virtually eliminate your chances of becoming infected. An early symptom of Lyme disease is usually, but not always, a rash where the tick was attached. The rash appears from three days to a month after the bite. It often starts as a small red area, then spreads, clearing up in the center so it looks like a donut. The rash is usually greater than 2½ inches in diameter. Flu-like symptoms such as fever, headache, stiff neck, swollen glands and fatigue are also common in the early stages. Prompt treatment of early symptoms with antibiotics can prevent more serious problems in the future. Untreated Lyme disease can lead to infection in the joints, nervous system and heart.
Babesiosis, which is a disease spread by deer ticks, is caused by a microscopic parasite that infects red blood cells. Human-to-human transmission can also occur during blood transfusion. In Massachusetts, the majority of cases are reported from Nantucket, Martha's Vineyard and Cape Cod. Most people who are infected with Babesia microti show very mild signs of illness or no signs at all. Symptoms occur gradually, usually one to four weeks after being bitten by an infected tick. They may include fever, chills, achy joints and muscles, fatigue, nausea, vomiting, abdominal pain and dark urine. Symptoms can last from several days to several months. Disease is most serious in people with immune deficiency, an absent spleen or in the elderly. In most cases, babesiosis is self-resolving, but more severe cases can be effectively treated with antimicrobials.
Tularemia is a bacterial disease that occurs in both animals and humans and can be spread to people in a number of ways. Humans can become infected through the bite of an infected tick. Infection can also occur after touching, handling or eating an infected animal, having contact with water or soil that has been contaminated by an infected animal, or being bitten by an infected animal. Animals most commonly infected include rabbits, squirrels, muskrats and beavers. Most of the cases in Massachusetts have occurred on Martha's Vineyard and have involved people inhaling contaminated particles during outdoor landscaping activities. Symptoms of tularemia vary depending on how the bacteria entered the body (e.g., by an infected tick bite, ingesting contaminated food or breathing in the germs). Tularemia of the lungs or bloodstream may be life threatening; however, tularemia can be effectively treated with antibiotics.
HGE, which is spread by the deer tick, is caused by bacteria that attack certain white blood cells called granulocytes. The disease occurs primarily in the southeastern and south central regions of the country. Symptoms of HGE usually begin to appear between one and three weeks after being bitten by an infected tick. Symptoms may be mild and can include fever, headache, chills, muscle aches and fatigue. HGE can be effectively treated with antibiotics. Early recognition and treatment are important to prevent potentially life-threatening complications.
WNV is a virus that can cause illness ranging from a mild fever to serious diseases such as encephalitis and meningitis. It is most commonly spread to people through the bite of an infected mosquito. It has also rarely been spread through blood transfusions or organ transplants. The majority of people who are infected with WNV have no symptoms. A small number have flu-like symptoms. Very few people go on to develop severe illness, but symptoms of such illness include high fever, headache, neck stiffness, disorientation, coma, tremors, convulsions, numbness and paralysis. There is no specific treatment for WNV. People with mild infections usually recover on their own. When WNV infects birds, it can cause death in certain species, including crows, blue jays and robins. The Massachusetts Department of Public Health collects information about the location of these types of dead birds to help identify areas where WNV may be active in Massachusetts.
EEE is a very rare but serious viral disease spread by infected mosquitoes. Outbreaks in Massachusetts usually occur every 10 to 20 years, with the most recent outbreak beginning in 2004. The first symptoms of EEE show up three to 10 days after a bite from an infected mosquito and include high fever, stiff neck, headache and fatigue. Encephalitis is the most dangerous and frequent serious complication. The disease worsens quickly, and patients may go into a coma within a week. There is no specific treatment for EEE. People who survive the disease will often be permanently disabled. Few people recover completely.
There are no vaccines available to protect against the vector-borne diseases summarized above. The only way to protect yourself is to avoid exposure by following the tips suggested below.
More detailed information and links to additional educational websites about vector-borne infectious diseases can be found on our Lyme Disease and West Nile Virus pages. It should be noted that individuals can be simultaneously infected with more than one of the tick-borne agents.