Mosquito-borne Viruses in Vermont

Mosquito-borne arboviruses inVT West Nile virus (WNV) Eastern equine encephalitis (EEE) Arboviruses: Arthropod – Borne- Viruses Arthropod definition: invertebrate animals (as insects, arachnids, and crustaceans) that have a segmented body and jointed appendages, and achitinous exoskeleton Includes mosquitoes and ticks Mosquitoes and ticks are the important arthropod vectors in VT.

Eastern Equine Encephalitis Virus Genus Alphavirus Family Togaviridae Outbreaks in horses recorded in 1831 Virus isolated in 1933 First human case confirmed in 1938 in MA Select agent Not new to the US. Probable horse cases back in the 1830s Virus is mostly present east of the Mississippi River – mostly along the coastal areas but also some inland swamps Present in Central and S. America – but different lineage of the virus Select agent- considered a potential BT agent

? Culiseta melanura Aedes, Coquillettidia, Culex species Amplifying hosts: Passerines – contain more than half of all bird species – perching songbirds, Small to medium body size Culiseta melanura is the enzootic vector – the species of mosquito that keeps the virus circulating among birds This species primarily bites birds but will occasionally bite mammals Bridge vectors – ones that bite birds and mammals – thought to be responsible for transmitting the virus from birds to mammals These 3 species may play a role but more recently it’s been proposed that Cs melanura is responsible for mammalian infections – may be why human illness is uncommon – this species bites humans and other mammals infrequently As for WNV – humans and other mammals are dead-end hosts Aedes, Coquillettidia, Culex species

EEE is Rare – Thankfully Most pathogenic mosquito-borne disease in the US Human case fatality rate ~35% Death more common in older people Among survivors, severe neurologic sequelae in ~50% (esp. children)

Symptoms – Human Incubation period 4 – 10 days Systemic Encephalitic Chills, fever, malaise, arthralgia, myalgia Duration 1-2 weeks Recovery complete as long as no CNS involvement Encephalitic Fever, headache, irritability, restlessness, drowsiness, anorexia, vomiting, diarrhea, cyanosis, convulsions, coma Two presentations – Systemic and Encephalitic

Other Species Affected horses and donkeys llamas and alpacas emus and pheasants also puppies, harbor seal, cow, African penguin, deer Vaccine licensed for horses – may also be effective in llamas, alpacas and emus

What Did We Know about EEE in VT? Until 2010 no evidence of the virus detected in VT Surveillance Passive human and veterinary surveillance Limited mosquito surveillance Seemed likely to be here… Found in neighboring states and Quebec Acidic hardwood swamps and vector species present Activity increasing in general in northeast?? New foci in ME and NH Increases in human cases in MA Although we hadn’t documented EEE in VT until recently, it seemed likely to be here. First of all, it had been found in our neighboring states and Quebec. Secondly, we have the enzootic vector, Culiseta melanura, here. And we have some acidic hardwood swamps – the preferred breeding habitat for that mosquito. Finally, there seems to be increased activity in New England in general.

Mosquito Surveillance Culiseta Habitat To look for EEE you want to look for habitat where the enzootic vector lives. This is the preferred habitat for Cs melanura. They overwinter as larvae deep in in crypts under tree roots – this makes it difficult to reduce their numbers with larvicides because it’s hard to get the chemicals into the crypts. Brandon, Leicester, Salisbury swamp area is our largest acidic hardwood swamp The first emergence in April and May are not infected with EEE. You can’t isolate the virus form mosquitoes until the second emergence. We don’t know exactly why that is. Acidic swamps (red maple, cedar) Crypts formed by pockets of water surrounding tree roots Brandon, Leicester, Salisbury area Adults emerge in April and May with second emergence in late June/July

Resting Box Passive collecting device Serves as a resting place for blooded mosquitoes from dawn to noon Attracts blooded, gravid, and host-seeking Culiseta melanura The best method for collecting this species.

This shows were potential bridge vectors and the enzootic vectors have been found in VT.

Deer Serosurvey for EEE virus 2010 hunting season Deer get bitten by a lot of mosquitoes Develop detectable antibodies Survive infection although clinical illness has been reported Limited range – ~1 square mile in summer Blood readily available 513 blood samples collected from deer and moose at check stations during youth weekend and opening weekend of rifle season Samples sent to CDC to test for antibodies against EEEV We started doing deer serosurveys in 2010. CDC partners with us on this project. They test the samples for us. Convenient samples – easy to obtain

Deer serosurvey - equipment Very simple equipment and little training needed to get samples. Samples collected by volunteers.

Youth weekend in Swanton.

Results of 2010 Serosurvey Deer – 50/489 (10.2%) Moose – 6/21 (28.6%) 8 positive yearlings This showed a surprisingly widespread distribution of virus. Surprising because most EEE virus had previously been found in close proximity to the acidic hardwood swamps. This study did not show any clustering of positive deer near known good Culiseta habitat.

What Did Deer Serosurvey Mean? EEE virus is present in Vermont Need to keep up surveillance – both human and veterinary More complete mosquito surveillance would be nice, but expensive Continue to educate Vermonters about preventing mosquito bites The virus is clearly here and is widespread. But since we hadn’t recognized any domestic animal or human cases in most of the state (until recently), the risk for transmission to people appears to be low.

Deer Serosurvey: 2010 - 2012 This map shows 3 years of data. Still shows evidence of widespread exposure in deer.

EEE in VT emus Sept 21, 2011 – report of ill emus Southern Rutland County – near large acidic swamp Several emus in a flock developed hemorrhagic gastroenteritis; ataxia Earliest onset 9/15 By 9/21, 14 emus had died Last death on 9/24 19/93 died, 2 ill birds recovered All ages affected First evidence of EEE causing illness in a domesticated animal in VT. Emus are very susceptible to this virus. Unlike mammals, they tend to get a viscerotropic form – it affects the GI tract and internal organs. In addition to developing neurologic signs they typically get a bloody diarrhea. The bloody secretions are infectious to other emu and potentially to people. Unlike horses, illness tends to go through the flock, often killing up to 30% of the animals. People must use caution when taking care of sick emus. Pheasants also can have a similar presentation.

2012 – Mosquito surveillance focused on EEE. Because of limited resources, mosquito surveillance limited to this area. This are was chosen because is has the only active mosquito control districts AND It is an area of high mosquito activity AND It has the largest hardwood swamp in VT This paid off, as the very first detections of EEE in mosquitoes in VT occurred in 2012 in this area. Most isolations were from one trap site and occurred for several weeks in a row starting in late July.

Unfortunately, mosquitoes weren’t the only ones infected Unfortunately, mosquitoes weren’t the only ones infected. About the same time we were learning about the virus being present in the mosquitoes, we learned about two possible human cases. Both of these people ended up being infected with the virus and dying from their illnesses.

Plans for 2013 Mosquito surveillance in known EEE area Surveillance data available on-line Human and veterinary surveillance Education to residents preventing mosquito bites On-line availability of a risk-map Updated throughout the season

WNV & EEE Prevention Promote use of personal protection Long sleeves and pants Insect repellent that contains DEET, Picaridin, or oil of lemon eucalyptus Cover baby carriages with mosquito netting Fix holes in screens Avoid outdoor activities when mosquitoes are active Eliminate mosquito breeding habitats Reduce standing water Vaccinate horses and other susceptible animals

Thank You