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Mosquito Control Vital to Fight 'Staggering' Consequences of Zika, WHO Says

by Maggie Fox /

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The potentially staggering consequences of Zika virus — severe birth defects and a paralyzing condition — make it imperative to control the mosquitoes that spread it, the World Health Organization said Tuesday.

With a vaccine more than a year away and no clear treatment, there’s one sure way to stop the virus, and that’s stopping the sneaky mosquito that carries the infection from person to person, WHO said.

WHO endorsed a variety of ways to kill the Aedes mosquitoes that spread Zika, dengue, chikungunya, yellow fever and other viruses. They include genetic engineering, irradiation and fish that eat the larvae.

WHO has already declared Zika to be a global public health emergency. It’s spreading in more than two dozen countries and moving at lighting speed across Latin America.

It’s the No. 1 suspect in what appears to be a startling increase in cases of microcephaly, a birth defect marked by an underdeveloped brain and head, as well as the paralyzing nerve condition called Guillain-Barré syndrome.

“If these presumed associations are confirmed, the human and social consequences for the over 30 countries with recently detected Zika outbreaks will be staggering.”

“Six countries (Brazil, French Polynesia, El Salvador, Venezuela, Colombia and Suriname) have reported an increase in the incidence of cases of microcephaly and/or Guillain-Barré syndrome (GBS) in conjunction with an outbreak of the Zika virus,” WHO said.

“If these presumed associations are confirmed, the human and social consequences for the over 30 countries with recently detected Zika outbreaks will be staggering.”

Teams are working to speed up development of a vaccine but they have to get a good test for it also. Quick blood tests get Zika mixed up with its related viruses such as dengue. Scientists were meeting in Washington, D.C. Tuesday to discuss measures.

“Although at least 15 groups are working on Zika vaccines, WHO estimates that it will be at least 18 months before vaccines could be tested in large-scale trials,” WHO said.

And the links with Guillain-Barre, a rare but puzzling condition that Zika was not known to cause, are even more troubling. “Even in countries with advanced health systems, around 5 percent of patients with the syndrome die, despite immunotherapy. Many require treatment, including ventilatory support, in an intensive care unit, sometimes for months up to a year, adding to the burden on health services,” WHO said.

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So mosquito control is the best way forward, WHO said. But it's not easy to fight Aedes.

“Most ominously, Aedes aegypti mosquitoes, which long bred in water collected in tree holes and the axils of plant leaves in forests, have adapted to breed in urban areas, flourishing in impoverished crowded areas with no piped water and poorly collected garbage and trash,” WHO said.

“Larvae have been found in a host of artificial containers, like discarded plastic cups and bottle caps, plates under potted plants, birdbaths, vases in cemeteries, and water bowls for pets. The mosquitoes can also breed in the microbial stew found in septic tanks, toilet tanks, and shower stalls.”

The eggs can survive dried out for a year and hatch the minute there are a few drops of water.

“Females often use ‘sneak attacks’, approaching victims from behind and biting on ankles and elbows."

“International trade in used tires is the best documented vehicle for introducing the mosquito to distant places,” WHO said. “Over the years, females have evolved to show distinct preferences: for human blood over that from other mammals, for shady resting places, for stagnant as opposed to fresh water, and for small artificial containers as the best place to lay their eggs,” WHO added.

“Females often use ‘sneak attacks’, approaching victims from behind and biting on ankles and elbows, which likely protects them from being noticed and getting slapped.” And they take little “sips” from multiple people, so they can infect people in batches.

Successful mosquito control programs have fallen apart, WHO said. “Resources dwindled, control programs collapsed, infrastructures dismantled, and fewer specialists were trained and deployed. The mosquitoes — and the diseases they transmit — roared back with a vengeance.”

Dengue infections have risen 30-fold in the past 50 years. So every method must be tested to control them, WHO said.

“For genetically modified mosquitoes, the WHO Advisory Group has recommended further field trials and risk assessment to evaluate the impact of this new tool on disease transmission. Trials previously conducted in the Cayman Islands showed significant reductions in the Aedes aegypti population,” WHO said.

“Another technique being developed involves the mass release of male insects that have been sterilized by low doses of radiation. When sterile males mate, the female’s eggs are not viable, and the insect population dies out. The sterile insect technique has been successfully used, on a large scale, by the International Atomic Energy Agency and FAO to control agriculturally important insect pests.”

WHO also calls promising a method that uses bacteria to infect mosquitoes and kill their eggs.

Larvae-eating fish can help but they cannot control mosquitoes breeding in trash and containers. Old-fashioned fogging using insecticides is also an important part of mosquito control, WHO said.

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