Cooperating counties and the Department of Environmental Protection began monitoring and surveillance activities this week for mosquitoes and ticks that carry West Nile Virus, Lyme and other diseases affecting people, according to Matt Helwig from DEPs Vector Management Program.

Activities to monitor mosquitoes and ticks are considered an essential function because they are designed to detect and prevent disease.

Mosquitoes

Helwig said he expects the mosquito population to still be rebounding from 2019 when Pennsylvania experienced its lowest level of West Nile Virus activity.

The state saw the highest level of West Nile activity in 2018 due to a lot of wet weather and warm temperatures.

He said West Nile activity was at its lowest level in 2019 because the most popular host for the disease-- birds-- crashed.  “It killed a lot of birds in 2018,” he explained.

“I wouldn’t anticipate an outbreak year [for West Nile Virus] this year, but I would anticipate West Nile Virus activity to continue,” said Helwig, “Because it’s [now] endemic in Pennsylvania.”

The warmer winter didn’t affect the lifecycle of Pennsylvania’s native species of mosquitoes, but Hilwig said, the Aedes albopictus-- the Asian Tiger mosquito that is often associated with carrying the Zika virus-- has a lower egg survival in cold weather.

Their territory may expand in the state he said 

Helwig added he does not expect to see Zika virus this year because the spread of the virus is largely dependent on foreign travel importing the disease to Pennsylvania and travel has been restricted due to COVID-19.

Ticks

Like mosquitoes, tick surveillance activities began this week by counties to determine what the population is and then testing determines what percentage of those sampled are carrying disease, said Helwig.

Just like mosquitoes, ticks are sensitive to weather conditions and warmer winters do not kill off as many ticks as a colder winter, which means a somewhat higher risk of Lyme disease from ticks.

DEP is in the second year of a five-year tick surveillance program being done in cooperation with the Department of Health to better understand tick population trends and the diseases they carry.

One result of the study is finding the invasive longhorned tick, that can spread disease in wildlife, livestock and people, has spread into seven counties in Pennsylvania-- Bucks, Chester, Delaware, Franklin, Montgomery, Northampton and Philadelphia.

He expects the longhorned tick to continue to expand its territory.

Tick sampling also found a rising percentage of adult blacklegged ticks infected with Lyme disease-- about half last year-- and about 12 percent of blacklegged ticks have been found carrying Anaplasmosis, which can infect people. 

The longhorned tick is also a known carrier of Anaplasmosis.

These results raised some flags with the Department of Health because they have seen a corresponding increase in the number of human illnesses related to Anaplasmosis.  There were 94 cases of Anaplasmosis in Pennsylvania in 2017 up from 6 in 2011.

Of course, this is nowhere near the 11,900 Lyme disease cases reported in Pennsylvania during 2017.

Control Measures

Helwig said the COVID-19 restrictions should not have a major impact on efforts to control mosquito populations either at the larvae or adult stages.

What has changed is the way public education is conducted to let people know how they can reduce their risk of disease from mosquitoes and ticks.

Helwig said in previous years they used a combination of public meetings and personal contacts to educate people on reducing risk so they can continue to enjoy the outdoors.

He said DEP and the counties are going to rely more on social media, flyers and other tools that involve no personal contact to get the word out.

For more information on vector-borne diseases and their prevention, visit the Department of Health’s Lyme Disease webpage [ticks] and DEP’s West Nile Virus webpage [mosquitoes].

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4/20/2020