When it Comes to Zika, Humans Are the Canaries in the Coal Mine

The Zika virus is spread by mosquitoes such as this one.
The Zika virus is spread by mosquitoes such as this one.
Photo by Muhammad Mahdi Karim, freely licensed under CC BY-SA 4.0.

If the mosquitoes in Dallas County are able to transmit the Zika virus, we won't know it until a patient is diagnosed. The main surveillance for the disease will have to involve a human case, said Dallas County Health and Human Services Director Zachary Thompson.

“In Miami-Dade, there were four confirmed cases and when they started going around and doing surveillance, they found the additional cases of Zika,” Thompson said. ‘They did not find positive mosquitoes as they were going through the process. They found positive humans.”

Florida is particularly prone to have local transmission of the virus given it has an abundant, year-round population of Aedes aegypti mosquitoes, the species that carries Zika. Though no mosquitoes tested in Florida have been found to be positive for Zika virus, there are 42 cases of locally spread transmission as of Aug. 29. The only way Florida health officials know the 42 cases are local, is that those who tested positive for the virus did not have a significant travel history.

DCHHS will follow in the footsteps of Florida if a local transmission of Zika occurs in the county, something that is expected to happen. If a localized case does occur in Dallas County, the city will react according to guidelines set by the CDC and in response to these “lessons learned” from Florida, Thompson said.

First, there would be ground application of larvicide around the home in which the infected person resides, fogging with both larvicide and pesticide up to 500 feet in some places. Control specialists would then systematically patrol the surrounding neighborhoods for mosquitoes to determine how far to continue the ground fogging. Aerial spraying of both larvicide and pesticide would be considered sooner rather than later, Thompson said.

Zika-carrying mosquitoes are active during the day, which would mean spraying would occur early in the morning and late afternoon, rather than at night like it does for mosquitoes carrying West Nile Virus, said Thompson.

“If you've got a localized case, you almost have to assume, or factor in, that there may be other cases,” Thompson said. “Given what happened in Miami-Dade it’s highly unlikely you're going to only have one localized case. That’s why as you're doing your surveillance you begin to prepare to do aerial spraying.”

The effort ramps up quickly after the initial diagnoses. "It’s anticipated you’re going to have additional cases," Thomspson said. "We would expand out to do door-to-door surveillance in that area beyond the required targeted spraying for that one house."

DCHHS has approached the city council about aerial spraying, stating they wanted approval from city council or a declared state of emergency by the mayor. In reality, county officials can decide to spray without either of those.

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“I have never seen anything convincing about (the efficacy of) aerial spraying, but it seems to me that this is a call the county’s going to make regardless,” said councilman Philip Kingston at a city council quality of life committee meeting last week.

Some county dwellers are more worked up than others. "No one is required by any laws to allow themselves to be exposed to chemical agents against their will, and to have that done to you, is an assault which is recognized worldwide as a war crime,” wrote Rev. Jake Harrison, founder of the group The Mindful Dissenter, in an email to the Observer. "No one in the city government can testify as to the full contents of those chemical agents; nor to the productive impact of the original goal, e.g. controling mosquitoes that may carry one of two different viruses, West Nile and or Zika.”

As of now, the plan appears to be fairly set if a Zika case occurs.

“If you've got two cases, then you definitely are going to have more cases, so you definitely need to say aerial spraying is going to be needed,” said Thompson. “We’re saying the likelihood of you finding it in the mosquito pool is going to be very small to none. You've gotta do a mitigation immediately to reduce the species.”


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