West Nile Virus an unpleasant surprise

West Nile Virus, according to State Epidemiologist Dr. Catherine Brown, is hard to predict in advance. In her words, it is “almost impossible to predict in advance of a season how bad it’s going to be.”

This year, as it turned out, the cases of WNV have turned out to be especially troublesome. Statewide, there have been 11 human cases and two animal cases. The percentage of mosquito samples testing positive this year for the virus, which is carried by birds and spread by mosquitoes, has about doubled the percentage last year.

In Worcester, WNV has been in news headlines on a regular basis. Most recently, this week spraying was expected to be done in two areas. The city is approaching double digits in spraying events. So far, however, no human cases of WNV have been detected in Worcester.

Worcester is looking mighty smart for joining the Central Massachusetts Mosquito Control Project earlier this year, even if it did so for an entirely different reason. In fact, the stated purpose for Worcester joining the CMMCP - at a cost of almost $150,000 a year - was over concerns of the Zika virus. The state had alerted city health officials of evidence of the Asian Tiger mosquito, which can carry the Zika virus, in Worcester. That let to a recommendation to join the CMMCP, which, among other services, provides spraying of mosquitoes.

Just this week. Brown told Worcester Magazine, “Zika we knew was, first of all there has never been Zika locally in Massachusetts.” Likewise, she said, the state wasn’t particularly concerned about eastern equine encephalitis, or EEE.

It turned out the virus least on the radar became the biggest problem.

“It was pretty early on in the season, based on mosquito surveillance, we were able to tell this was going to be a tough year for West Nile Virus,” Brown said.

High heat and heavy rain have made Worcester and many other cities and towns around Massachusetts big targets for mosquitoes, particularly the Culex, which have overwhelmingly been the species testing positive for WNV. Climate change is being seen as a culprit, with more extreme weather patterns featuring higher temperatures and longer-lasting rain events that have led to flooding.

A deeper issue involves the birds carrying WNV. As quoted in a story elsewhere in this issue, Brown said more birds than normal had to be carrying the virus at the beginning of the season in order for so many mosquitoes to be testing positive. That is alarming and bears further study.

In the meantime, for the remainder of the season and perhaps into early fall, even with cooler weather having entered the area this week, people should pay careful attention to their exposure to mosquitoes - and to the habitats that breed them. WNV is not typically deadly, but it can be. It can also be particularly troublesome to older individuals or those with compromised immune systems.

It may not have been the virus local health officials expected, but WNV has certainly made its mark this year.