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HomeUncategorizedLow mosquito counts in Hernando, but nearby areas report arbovirus presence

Low mosquito counts in Hernando, but nearby areas report arbovirus presence

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It has been a wet spring and summer has brought rains which have kept up the water level. There are several areas in Hernando County with significant standing water where there usually is not water. There have also been cases of Eastern Equine Encephalitis (EEE) and West Nile found in nearby counties. These factors could lead to a mosquito problem. 

On Monday The Hernando Sun spoke with Mosquito Control Director Sandra Fisher-Grainger and she gave an update on the current mosquito situation in Hernando County.  Although there has been a lot of rain, and there is much standing water around the county, Grainger’s report is positive, with findings of very low mosquito activity at the moment.  However, she is cautious with the possibility of more rain that could saturate the ground for longer periods of time which leads to increased mosquito breeding.  Additionally, counties around Florida are discovering West Nile positive mosquitoes as well as West Nile positive sentinel chickens. In recent months, Central Florida counties have found Eastern Equine Encephalitis (EEE) in mosquito pools, horses, emus and sentinel chickens.

Weekly reports from the Department of Health summarize the latest activity of arboviruses in Florida.  The most active of those diseases currently is EEE and West Nile.  For West Nile Virus Activity The July 22- 28 report states, “One human case of WNV infection was reported this week in Bay County. No horses with WNV infection were reported this week. Four mosquito pools tested positive for WNV this week in Sarasota County. Thirteen sentinel chickens tested positive for antibodies to WNV this week in Alachua, Bay, Nassau, Polk, and Walton counties. In 2018, positive samples from one human, one blood donor, one crow, eleven mosquito pools, and fifty sentinel chickens have been reported from eleven counties.”

The report for EEE states, “No human cases of EEEV infection were reported this week. No horses with EEEV infection were reported this week. Eleven sentinel chickens tested positive for antibodies to EEEV this week in Nassau, Orange, Putnam, St. Johns, and Walton counties. In 2018, positive samples from one human, forty-four horses, one mule, one donkey, one owl, one emu, five emu flocks, two mosquito pools, and one hundred sixteen sentinel chickens have been reported from thirty-one counties.”

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Grainger explained many of the treatment and surveillance strategies they utilize in the mosquito control department.  She said that any area of standing water they are aware of gets treated regularly. 

“A lot of areas that we know the water is standing all the time gets treated regularly and as we get more water and the ground becomes saturated so that the water is not percolating directly into the soil, the technicians are out doing treatments of that water.”

Treatment, she explained is a combination of spraying and the use of mosquitofish.  

“Any area that’s a permanent body of water such as a drainage retention area that always has water or if it’s a woodland pool or a freshwater wetland, we’ll put fish in those because we don’t want to put fish somewhere where the water’s going to eventually evaporate or percolate into the ground.”

Mosquitofish are tiny freshwater fish that consume a large amount of mosquito larvae in comparison to their body size. In circumstances where they cannot utilize mosquitofish, Grainger says-  

“Otherwise what we use are called larvacides which is basically a pesticide that targets the mosquito larvae that are developing in the water.  The products that we use are all bacterial based or they are insect growth regulators which basically is tricking the mosquito larvae into believing that it’s already fully grown… and they basically starve to death.”

Residents should contact mosquito control if they are experiencing a mosquito problem.  Grainger described the service request process, 
“When someone calls for a service request, we will come out to the property and check the property and the property of residents that surround them. We’ll also check any drainage retention area, catch basin or storm drain in the area and try to identify the problem.  The majority of the service requests we have right now are almost all coming back as people breeding mosquitoes in containers on their own property.”  

She continued, “We set traps throughout the county and trap counts have been very very low and so have our landing rate counts.  Mostly what we’re seeing right now are container breeding mosquitoes.” 

Grainger said that landing and trap counts are low because the ground hasn’t been saturated for enough time to allow mosquito larvae to develop.  
“As we continue to get rain daily, the ground has to become saturated to a certain percentage for the water to stand long enough for the mosquitoes to develop.  Depending on the species, they can take anywhere from 5 to 10 days to develop.  If that water is there this morning or this afternoon and it’s gone tomorrow then you know that’s not enough time for them to hatch.  That’s basically what we’re seeing right now and why our trap counts are so low.”  

As far as traps in the county, Mosquito Control sets 16 traps every week. “These are called CDC traps which use dry ice as bait because it produces CO2 which mimics a human or animal exhaling. We also do landing rate counts three times a week at 25 different locations.  A technician will stand fully covered and allows mosquitoes to land on him and he counts how many he gets in a one minute time period,” Grainger stated.

Landing rate counts and traps are considered surveillance.  “We’ve had some of the lowest surveillance numbers in a couple of seasons now,” said Grainger.  She erred on the side of caution though, because with all the rains we’re getting right now- that could make the problem worse.

“Even though it was a real rainy spring, there was some time when the ground was able to get rid of the water… We will get to a point though where the ground will be saturated enough for the water to stand longer,” remarked Grainger.

During Irma she explained, “There was a lot of water dumped at one time and it didn’t have anywhere to go.  This was on the east side of the county.  The west side of the county didn’t see mosquito numbers the way the east side did.  That was because the water didn’t have anywhere to go because the (Withlacoochee) river was flooded.  We do still see standing water in catch basins and storm drains- those particular storm structures were treated this past spring.  Hundreds if not thousands of storm drains and catch basins were pretreated this spring so that prevented a lot of breeding that might have occurred when the rains started coming in on a daily basis.”

About West Nile or EEE showing up in the county she said, “It’s always possible.”

She recalled,  “A couple of years ago we had two horses go down with West Nile virus.”   We have five chicken coops throughout the county that get tested on a weekly basis.  We have not had one positive.”

Grainger continued, “We have West Nile to the south of us but we also have EEE which has been killing horses in areas such as Marion County and mostly the central area of the state.  Eastern Equine Encephalitis is a far more serious disease. I’m worried about West Nile, but I’m more worried about Eastern Equine Encephalitis.”

However, the mosquito numbers they are finding in the field now aren’t warranting drastic concern.

“We haven’t had any positive chickens this year at all for any disease and we haven’t had any travelers with any kind of disease come into the county such as Dengue, Zika or Chikindungya.  Quite frankly, the vectors that are the mosquito species that carry West Nile- the numbers are so low- we would need a lot more mosquito numbers for that to be more concerning.  To be more concerned I would need to see the numbers of those particular species be very high and that just hasn’t happened this year.”

Grainger elaborated on the serious situation immediately following Hurricane Irma which resulted in aerial spraying.

“For example, right after Irma last year, the species that first popped off after the storm, they’re called Psorophera ferox and Psorophera howardii- it’s a nuisance mosquito.  They do not carry disease.  They were first to develop and become adults because they lay their eggs on moist soil.  As soon as the water got into areas and the eggs were laid- they immediately started to develop and in less than 7 days they were on the wing.  Now what happened after that is that the vector for West Nile virus- Culex nigripalpus- they lay their eggs on the surface of water.  So while the Psorophora had already hatched, the nigripalpus lay their eggs.  So within 5 to 7 days after the nuisance attack by the first mosquitoes (Psorophora), the vector species developed into adults.  That’s when things became very concerning and that’s why we ordered the aerial spray.  There were areas that were flooded that we couldn’t get a truck into.”

Mosquito Control were running 4 to 8 trucks after Irma between morning and evening in order to treat the areas they could reach.  Right now,  they are running one or two routes a night.

Grainger says, “We’re not even spraying every night because the numbers just aren’t there. We have to have numbers in order to justify to the state that there was a reason to send a truck.  That either comes from the trap counts, landing rate counts or it’s a technician that’s responding to a service request where they experience a large number of adults.  That’s how we decide whether we’re going to spray and these container breeders that we’re finding on people’s properties can’t be controlled with a truck.” 

The best way to control container breeding mosquitoes is for residents to check for any standing water containers on their property once a week.  This includes checking gutters, boats to make sure they’re properly drained, tarps to make sure they’re taut so that water does not accumulate and especially tires.

Currently Mosquito Control is not testing mosquitoes that they trap.  

“We haven’t had any chickens come up positive, we haven’t had enough mosquitoes for it really to be worthwhile,” Grainger said.  
She explained that you need to test a large number of mosquitoes in order to get the positive results and it’s helpful when you know it’s in the bird population.

“You have to test a lot of mosquitoes to get those positives.  It’s sort of like a needle in a haystack.  You’re chances of finding them are better when you know already that they’re in the bird population.  It used to be that throughout the country they submitted dead birds on a regular basis- they just don’t do that anymore.  Primarily because the birds are becoming immune- they’re carrying the virus but not dying from it anymore.”  

The Florida Wildlife Conservation Commission does collect data on dead bird findings which can be reported to www.myfwc.com/bird/.  Although the birds reported could have died from any number of causes, it could be an indication of arbovirus circulation in an area.  In 2018, 288 reports representing a total of 737 dead birds (17 crows, 20 jays, 60 raptors, 17 doves) were received from 41 of Florida’s 67 counties. 

Also with the CDC traps, a  large portion of the trapped mosquitoes are dead by the time they bring them back to the lab due to heat exhaustion.  “When we want test mosquitoes, we use specialized traps that capture mosquitoes that have already taken a blood meal.  We are targeting female mosquitoes that are looking to lay their eggs- which is called a gravid trap. The mosquito comes across a container of sticky water we put out and she goes to lay her eggs on the surface and it has a fan attached to it that basically sucks her in there.  We only put it out for a day.” When mosquitoes get back to the lab, they are frozen immediately so that the RNA is frozen with them.  If they die out in the field- the technology can’t test for virus.

Although Hernando County is not currently testing mosquitoes, they will be doing so in the near future.  With the support of state and local funding.
Last year, Hernando County’s Mosquito Control department was awarded a $75,000 grant from the Florida Department of Agriculture and Consumer Services (FDACS) to purchase equipment for real-time testing of mosquitoes for diseases. This would eliminate the weeks of waiting for the virus to incubate in chickens or for mosquitoes to be sent to labs for testing. The County provided $22,500 in matching funds.

The county states, “With in-house testing capabilities, populations would be monitored weekly for all viruses that have previously been found in the County, thereby conferring immediate action to the threat of an outbreak if a positive pool of mosquitoes is found. This work would also allow the department to better understand hosts and vectors involved in transmission of these viruses as any of the samples could also be forwarded to Universities for further DNA analysis, as the initial phase of this process would have already been completed by the Hernando County Mosquito Control Department.”

“Our laboratory is almost complete for us to start testing the mosquitoes ourselves,” said Grainger.  She explained that one species she will be testing is Culex quinquefasciatus because it can carry West Nile in their bodies and it can tell you if West Nile is in the area.

Because there has been arbovirus activity in surrounding counties, Grainger stresses vigilance in wearing mosquito repellent while outdoors and checking for containers with standing water regularly.    

To request service to your property call Mosquito Control at (352) 540-6552. 

You can also request online: http://www.hernandocounty.us/departments/departments-f-m/mosquito-control 

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