An Essex County man in his 70s is hospitalized with Eastern equine encephalitis—the fifth Massachusetts resident this season to be stricken with the often-fatal, mosquito-borne illness, state health officials announced Tuesday.

The officials also said that a man in his 40s from Greater Boston has been diagnosed with West Nile virus, another disease spread by mosquitoes that typically produces a less serious illness.

Disease trackers also confirmed another case of eastern equine in a horse, stabled in Plympton.

Advertisement - Continue Reading Below

Here is the announcement from the Massachusetts Department of Public Health:

“Mosquitoes are still active in the environment until the first hard overnight frost, so it’s important to keep taking common-sense precautions against mosquito bites until then,” said Department of Public Health State Epidemiologist Dr. Al DeMaria. “Use insect repellant, cover up exposed skin, and avoid being outdoors at dusk and after nightfall when mosquitoes are at their most active.”

There have been five confirmed human cases of EEE in Massachusetts residents so far this year, including one case that resulted in the death of a Worcester County man in his 70s. There were two cases of EEE in August of last year acquired in Massachusetts; a fatal case in a Bristol County man and an infection in a tourist from out of state. EEE activity in both 2010 and 2011 raised public concern and prompted DPH to work with a panel of experts to evaluate and enhance the state’s surveillance and response program. EEE is spread to humans through the bite of an infected mosquito. Initial symptoms of EEE are fever (often 103º to 106ºF), stiff neck, headache, and lack of energy, and in severe cases can progress to confusion, disorientation, and coma. EEE is a serious disease in all ages and can even cause death.

WNV infected mosquitoes have been found in 107 communities from nine counties so far during 2012, and health officials predict that the state is on track to have the greatest number of WNV-positive mosquito pools since WNV was first seen in Massachusetts in 2000. There have now been 15 human cases of WNV in Massachusetts this year, one of which resulted in death. There were six cases of WNV in Massachusetts residents and one in a horse last year. While WNV can infect people of all ages, people over the age of 50 are at higher risk for severe disease. WNV is usually transmitted to humans through the bite of an infected mosquito. Most people infected with WNV will have no symptoms. When present, WNV symptoms tend to include fever and flu-like illness. In rare cases, more severe illness can occur.

People have an important role to play in protecting themselves and their loved ones from illnesses caused by mosquitoes:

Apply Insect Repellent when Outdoors. Use a repellent with DEET (N, N-diethyl-m-toluamide), permethrin, picaridin (KBR 3023), oil of lemon eucalyptus [p-methane 3, 8-diol (PMD)] or IR3535 according to the instructions on the product label. DEET products should not be used on infants under two months of age and should be used in concentrations of 30% or less on older children. Oil of lemon eucalyptus should not be used on children under three years of age.

Be Aware of Peak Mosquito Hours. The hours from dusk to dawn are peak biting times for many mosquitoes. Consider rescheduling outdoor activities that occur during evening or early morning.

Clothing Can Help Reduce Mosquito Bites. Wearing long-sleeves, long pants and socks when outdoors will help keep mosquitoes away from your skin.

Drain Standing Water. Mosquitoes lay their eggs in standing water. Limit the number of places around your home for mosquitoes to breed by either draining or discarding items that hold water. Check rain gutters and drains. Empty any unused flowerpots and wading pools, and change water in birdbaths frequently.

Install or Repair Screens. Keep mosquitoes outside by having tightly-fitting screens on all of your windows and doors.

Animal owners should reduce potential mosquito breeding sites on their property by eliminating standing water from containers such as buckets, tires, and wading pools – especially after heavy rains. Water troughs provide excellent mosquito breeding habitats and should be flushed out at least once a week during the summer months to reduce mosquitoes near paddock areas.

Horse owners should keep horses in indoor stalls at night to reduce their risk of exposure to mosquitoes. If an animal is diagnosed with WNV or EEE, owners are required to report to DAR, Division of Animal Health by calling 617-626-1795 and to the Department of Public Health (DPH) by calling 617-983-6800.

More information, including all WNV and EEE positive results from 2012, can be found on the Arbovirus Surveillance Information web page or by calling the DPH Epidemiology Program at 617-983-6800. The findings of the DPH Eastern Equine Encephalitis Expert Panel were released earlier this year.