DIVISION OF PUBLIC HEALTH SERVICES
DEPARTMENT OF PUBLIC SAFETY
Mosquito and Vector Control
||First Hunterdon Horse Victim
of West Nile Virus
Press Release Dated:
September 17, 2003
"We never like to hear about a horse getting West Nile virus, but we were bracing for this kind of news all season," said Mosquito Control and Vector team leader Tadhgh Rainey as he described the lead up to the first confirmed equine case of WNV in Hunterdon. Rainey's group, a unit of the Hunterdon County Department of Health, counseled residents all season long about WNV, both in the field and through the media. "Since spring, we've reported evolving conditions pointing to a serious mosquito problem. With WNV confirmed here in the county horse population, horse owners and caretakers will want to be doubly sure that water in troughs and drinking pools is kept fresh." Standing water sources nearby horse facilities can and frequently do provide perfect breeding spots for mosquito populations.
But mosquitoes alone are not where the problem begins. WNV is an arboviral disease, meaning it is carried in host birds, crows the key subject. Throughout Hunterdon, 40 dead crows out of the 55 specimens tested for WNV were positive with the disease. While alive, these crows provided both a host system for WNV and a blood meal for mosquitoes who could pick up the disease and carry it forward, injecting it into horses or humans they encounter.
"We've received more than 150 calls from county residents, telling us they spotted a dead crow in their yard or nearby," Rainey said. "But not every crow specimen is suitable for lab testing. Many of the birds called in to us can't be used because they don't fit the state criteria of 'acceptable specimens for testing," Rainey explained. "For the state lab to take a specimen, the bird has to be dead less than 24 hours and be intact. We've seen crows already in advanced decay with maggot activity. In this stage, these are not useful specimens." Rainey added that another common reason for bird specimens to be rejected for testing by the state lab is misbagging. "The state has strict guidelines on how dead crows should be packaged."
Statewide, 1202 crows have been tested. Of the samples, 426 crows found in 20 counties were confirmed positive with WNV. Of the 6,292 mosquito pools tested, 215 positive pools were found. Data provided by the state also tracks the human-WNV condition. To date, more than 100 New Jersey residents have been tested for WNV with six cases confirmed positive, including one blood donor. Fifty-four of the human cases tested negative, eighteen are pending, and samples were not yet received for the remainder.
The infected horse in Ringoes is presumed to be recovering. Rainey said the horse most likely was vaccinated for WNV but there was no way to confirm if it underwent the complete vaccination regimen. "Considering the severity of this mosquito season, we're lucky in Hunterdon," Rainey said. "Statewide to date, there are 32 positive horse cases. We only have one. But nobody on the team likes to get news about even one case happening in county. Three out of 10 horses acquiring WNV aren't going to make it, so we're disheartened whenever we hear something like this."
Apparently, the season isn't over until it's over. According to Rainey, "We're not out of the woods yet. Traditionally equine activity occurs well into October, if not later."
With the sizable equestrian population in Hunterdon, Rainey pointed out that horse owners should ensure their animals are immunized. "Too many people don't feel this is a high priority," Rainey said. "But the late summer-early fall period is the most serious time for WNV transmission. Although it remains unclear how effective the immunization is, we remind horse owners that it is still the main defense available."
The Hunterdon health department is discovering that mosquito activity affecting horses is not always found in areas where human-mosquito encounters spawn numerous 'nuisance' calls. While still theoretical, it's entirely possible that the mosquitoe type feeding on horses is different than that which prefers humans. Pointing out that this enigma adds to the difficulty of getting ahead of the disease, Rainey said, "The impact of this finding suggests that WNV activity affecting horses might occur in areas where it wouldn't be expected simply because the human-mosquito encounters have not prompted residents to call. Overall, we're finding WNV scattered widely throughout the county and in no specific pattern. But this part of the science comes as no surprise to us."
The Hunterdon health department also uses technology to track WNV. "Using our global information system (GIS), we map our mosquito trapping sites to monitor activity experienced at those sites," said Rainey. "This gives us a visual picture of the changing dynamics of hot spots and newly emerging active zones." For a current picture of WNV activity, visit http://www.co.hunterdon.nj.us/health/westnilemap.htm.
"At this point, we're hoping we catch a meteorological break," Rainey said, looking beyond the rainfall predicted with approaching Hurricane Isabel. "This coming fall can't get here soon enough. That will give us some time to comprehensively analyze the many samples we're accumulating. We start next year's battle plan immediately after this year's activities wind down. With county support, we'll give next year's mosquitoes the fight of their life."