Experts probe Zika mosquito control, more microcephaly

A World Health Organization (WHO) emergency committee that recently assessed the possibility of using five new mosquito control tools in the battle against Zika virus said properly used existing methods are effective, but they opened the door to using two new strategies in limited and monitored pilot projects.

In other developments, Panama reported its first possible Zika-linked microcephaly case, and the US Centers for Disease Control and Prevention (CDC) recently added Cuba to its travel advisory for pregnant women.

Also, the WHO's Pan American Health Organization (PAHO) said in its most recent epidemiologic update that Zika virus cases are tapering in the Americas, but activity is rising in some locations, including the Dominican Republic, French territories, Haiti, and Venezuela.

Meanwhile, the number of illnesses in Puerto Rico and other US territories continues to climb, along with travel-related cases on the US mainland, the CDC said. The territories have recorded 283 local cases, including 35 in pregnant women, as of Mar 16, most of them in Puerto Rico. In the continental United States, 258 travel-related cases have been reported, including 18 in pregnant women and 6 due to sexual transmission.

Mosquito control recommendations

The WHO's vector control advisory group met in Geneva on Mar 14 and 15 to see if any of the newer mosquito control methods would be useful and what issues might crop up if they were used. The panel explored the issue in light of the view that traditional measures such as spraying haven't been able to interrupt dengue transmission, raising worries about their ability to help much with curbing the spread of Zika virus.

The new technologies they considered included Wolbachia bacteria, transgenic mosquitoes (Oxitec OX513A), sterile insect technique (SIT), vector traps, and attractive toxic sugar baits.

In a position paper on the deliberations released Mar 18, the group said that if current methods such as targeted residual spraying of Aedes mosquitoes in and around houses are implemented well—quickly, comprehensively, and sustained—they offer the most effective way to stop Zika virus transmission. The other current tools were space spraying and indoor fogging, eliminating Aedes mosquito breeding sites, and personal protective measures such as wearing protective clothing and wearing recommended insect repellent.

Group members also recommended carefully designed pilot deployment of two of the new tools, alongside rigorous independent monitoring and evaluation: release of mosquitoes carrying Wolbachia bacteria, which suppress virus development, and transgenic mosquitoes designed to reduce mosquito populations by preventing Aedes larvae from reaching adulthood. Randomized control trials with epidemiologic outcomes should continue to build evidence before the two tools are used routinely, the group noted.

They said more evidence is needed before pilot projects can be considered for the three other methods: SIT, vector traps, and attractive toxic sugar baits. Though SIT is a promising new tool for reducing mosquito populations, carefully planned pilot studies should be done to build support for its use, the group said. The experts added that the WHO should work closely with the United Nations Food and Agriculture Organization and the International Atomic Energy Agency to develop guidance on the epidemiologic impact to support its evaluation and use by countries.

For vector traps that can attract and kill egg-laying female mosquitoes, efficacy has only been shown in limited field trials and more studies are needed to gauge feasibility for large-scale use, the group found. And attractive toxic sugar bait methods need further assessment for mosquito and epidemiologic impact, as well as risk assessment for acceptability, compliance, and exposure.

Overall, the group said the battle against Aedes mosquitoes needs to change from a reactive approach to sustained, proactive interventions. "The focus must be on improving the quality and extent of implementation of vector control interventions to ensure optimal impact—both within the context of the immediate response to Zika virus disease and, more broadly, against all Aedes-borne diseases," they said in a meeting summary.

In a related development, the WHO's European regional office said in a Zika virus vector risk assessment that the risk of the virus in Europe will increase in late spring and summer. A aegypti, the main Zika virus vector, has been found in limited areas of the European region, including Madeira and the northeastern Black Sea coast, including Georgia and the southern part of Russia.

The office warned, however, that A albopictus—present in 20 European countries— is capable of carrying Zika virus and is a potential vector. It added that countries in the region need to be well prepared to protect their populations from the spread of Zika and its potential complications.

Microcephaly developments

Scientists in Panama reported the country's first potentially Zika-linked microcephaly case, according to a report yesterday from Telesur, a television network based in Venezuela. The country's Gorgas Memorial Institute said the child died 4 hours after birth and had an underdeveloped brain and an abnormally small head. They said Zika virus was detected in the baby's umbilical cord.

So far the only countries that have reported Zika-linked microcephaly cases are Brazil, which has been the outbreak's epicenter, and French Polynesia, which had an outbreak in 2013 and 2014.

Meanwhile, the WHO announced that it will be part of a joint mission to Cabo Verde to manage a Zika virus outbreak there and investigate a case of suspected microcephaly, based on a request from the country's health ministry. In a Mar 18 statement, the WHO said Cabo Verde's outbreak is declining, but it reported its first microcephaly case on Mar 15. The team also includes experts from the WHO's African regional office and the Pasteur Institute in Dakar.

Of 7,490 suspected Zika cases so far, 165 are in pregnant women, including 44 who have delivered their babies with no complications or abnormalities. Some of the country's islands have had no Zika virus, and on some, no cases have been reported since the middle of February.

Travel advisory expands, test approved, countermeasure meeting

  • The CDC on Mar 19 added Cuba to its growing list of locations reporting local Zika virus spread. The CDC first issued its level 2 travel alert on Jan 15, advising pregnant women and those planning on becoming pregnant to consider postponing travel to areas where the virus is circulating. The list has grown to 38 countries or territories. It modified the guidance on Mar 11 to exempt destinations above 6,500 feet where Aedes mosquitoes are rare. The addition of Cuba to the list came 1 day before President Obama, his family, members of Congress, and others arrived for an official visit to the country.
  • The Food and Drug Administration (FDA) on Mar 17 issued an emergency use authorization (EUA) for a multiplex test to help doctors distinguish if patients have chikungunya, dengue, or Zika virus, based on a request from the CDC. The CDC said in a statement that the test can help streamline diagnosis. The agency will start distributing it during the next 2 weeks to qualified labs in the Laboratory Response Network.
  • The US Department of Health and Human Services is hosting an expert meeting on Mar 28 and 29 to speed the development of Zika virus countermeasures. According to background information from the National Institute of Allery and Infectious Diseases (NIAID), the meeting will take place in Bethesda, Md., and will be streamed live as a webinar.

See also:

Mar 18 WHO mosquito control statement

Mar 18 WHO mosquito control emergency meeting summary

Mar 17 PAHO epidemiologic update

CDC update on Zika virus in the United States

Mar 18 WHO European regional office vector risk assessment

Mar 14 CIDRAP News story "WHO emergency vector control group meets in Geneva"

Mar 20 Telesur report

Mar 18 WHO statement on Cabo Verde joint mission

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