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Pet Health Ingredients Shown Effective Against Mosquito-Borne Diseases

Baby with microcephaly

Baby with microcephaly (Harold Ruiz, PAHO)

3 July 2018. Researchers in the U.S. and the Netherlands found ingredients in over-the-counter products to control fleas and ticks in house pets can also help prevent infectious diseases in humans spread by mosquitoes. A team from California Institute for Biomedical Research or Calibr — an affiliate of Scripps Research Institute — in La Jolla, and Tropiq Health Sciences, a social enterprise in Nijmegen, the Netherlands, describe their discoveries in yesterday’s issue of Proceedings of the National Academy of Sciences (paid subscription required).

The team led by Calibr’s and Scripps Institute’s Matt Tremblay and Koen Dechering, CEO of Tropiq Health Sciences are seeking simple and inexpensive methods for controlling mosquito-borne diseases, particularly where mosquitoes feed on human blood. Among the most troublesome and continuing global health problems are malaria and Zika virus, both spread by mosquitoes. Malaria is caused by infections from the plasmodium parasite transmitted by mosquitoes. In humans, the parasite multiplies in the liver, then infects red blood cells. World Health Organization says 216 million people were afflicted with malaria in 2016, leading to 445,000 deaths, primarily in sub-Saharan Africa.

Zika is also spread by mosquitoes, and according to WHO is now found in 70 countries, mainly in the Americas and southeast Asia. In addition to mild joint pain, headache, and rash, the Zika virus is also associated with birth defects including  microcephaly and Guillain-Barré syndrome.

The Calibr-Tropiq team investigated a potential solution to preventing mosquito-borne infections with a class of drugs called isoxazolines, best known as the active ingredients in over-the-counter drugs given to dogs to control fleas and ticks. Isoxazoline drugs like fluralaner and afoxolaner work by binding to receptor proteins found in nerve and muscle cells in insects, but not in mammals, thus paralyzing and killing the insects. The drugs are given orally to the pets, and absorbed into their blood streams, where they stay active for up to 3 months, and are transmitted to fleas and ticks when they feed on the pets’ blood.

In this case, the researchers tested fluralaner and afoxolaner in the lab on mosquitoes and other insects, including Anopheles and Aedes mosquitoes responsible for malaria and Zika virus respectively. The team also tested the drugs with Culex mosquitoes that spread West Nile virus and Phlebotomus sand flies that spread parasites responsible for the tropical disease leishmaniasis. The tests mixed the drugs with blood in concentrations similar to safe levels in mammals, which killed the insects after feeding. The tests included strains of the insects considered resistant to common insecticides.

With colleagues from Imperial College London, the researchers constructed a statistical model for estimating the impact of providing drugs based on these ingredients to populations where these infectious diseases are endemic. The team found giving isoxazolines to 30 percent of the population where Zika is common could prevent at least 97 percent of those cases. Where malaria is a problem, such as in Africa, the effect is less dramatic, but still impressive: 70 percent of malaria cases could be prevented with 30 percent of the population given isoxazolines.

The authors caution that isoxazolines do not work like vaccines to prevent infections in humans, but the drugs would kill the insects before they infected others. As Tremblay explains, however, in a Scripps Institute statement, “Isoxazolines could be administered prior to the beginning of seasonal disease outbreaks to convey protection until the threat diminishes at the end of the season.”

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