PENNSYLVANIA STATE REPORT

Judy Cherepko

PA Vector Control Association

ABSTRACT

West Nile virus has really reared its ugly head this year in Pennsylvania. Because of the mild winter and warm temperatures in early spring, the virus became established in the Culex mosquito population leading to numerous WNV positive horses, humans and dead wild birds this summer/fall. Surveillance in the state identified the highest number of positive mosquito pools since the program began in 2000, almost tripling the previous high of last year. To date, the state has reported WNV positives in; 24 humans (1 deceased) , 4 blood donors, 41 horses, 132 dead birds and 3372 mosquito samples (4263 pools). It is anticipated that the human cases will increase substantially because of the delay involved in testing and reporting of additional cases.

The virus was primarily detected in Culex species in 2012. Culex pipiens (around 3,000 pools) had the greatest number identified while Culex restuans (~1100 pools) had the second highest number of pools. The virus was also detected in Culex salinarius (16 pools) and Culex erraticus (4).

A number of bridge vector collections also detected West Nile this season. Aedes albopictus (4 pools), Aedes vexans (3 pools), Ochlerotatus japonicus (4 pools), Anopheles punctipennis (1 pool), and Psorophora ferox (1 pool) were typical mammal feeders that also tested positive for West Nile.

As a result of the activity, DEP and its county partners have larvicided and adulticided continually since early June. Larval control was directed toward treating catch basins in more populated municipalities, towns and cities while also inspecting and treating if necessary wastewater treatment facilities in areas where human populations were at the greatest risk. Typically ULV truck spraying is the last option in PA, beginning in early August but the program had to mobilize the trucks much earlier this season as a result of the high WNV infection rate detected in the mosquito populations.

A positive EEE horse was also reported in Luzerne County in early September. Mosquito surveillance identified the presence of Culiseta melanura in the vicinity of the bordered horse but those mosquitoes tested negative for the virus. A number of bridge vectors were also collected but those also were negative for EEE.

Pennsylvania has had Ae. albopictus nuisance problems in the southeastern portion of the state since 2005 but it has gradually expanded westward into southcentral PA over the past three years. This mosquito became the “Number 1” nuisance mosquito complaint that the program received from citizen submissions in 2012. We have implemented some of New Jersey’s recommended control strategies directed at reducing Asian tiger mosquito populations but are really hoping for a very cold winter to cause egg mortality and therefore letting nature take care of this problem for us.

The state continues to support the largest black fly suppression program in the world, its mission to reduce nuisance black fly adults during the outdoor recreational months from mid-April to August. Pennsylvania aerially treated 40 rivers and streams throughout the state, targeting the Simulium jenningsi complex, which is an aggressive nuisance black fly in the Commonwealth. The program used around 82,000 gallons of Bacillus thuringiensis israelensis (Bti) to combat this pesky insect in 2012.