Scientists Target Mosquito-Borne Illness

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Of all the disease-spreading insects in the world, the mosquito poses the greatest menace, according to the World Health Organization (WHO).  As if to underscore that threat, two mosquito-borne viral diseases have begun to spread well beyond their points of origin.  One is dengue fever, a potentially deadly illness, and the other is chikungunya, a debilitating and painful disease from which most people can recover. There are no vaccines to prevent these diseases.  But researchers are working hard to develop vaccines against dengue fever and chikungunya, and to control the mosquitoes that spread them.

Scientists have identified at least 3,000 different species of mosquitoes throughout the world. The Asian tiger mosquito is one that bites during the day.

The tiger mosquito’s bite is more than annoying. It’s responsible for infecting 20 million people a year with dengue fever, a flu-like illness that can result in hemorrhagic fever, shock syndrome, and even death.

“It’s almost completely spread throughout the tropics and subtropics throughout the world,” said Weaver.

Scott Weaver at the University of Texas Medical Branch confirms what other scientists are seeing, mosquitoes that can transmit dengue fever have spread though India, Southeast Asia and Latin America and are finding their way around the world. There were more than 12 confirmed cases this year in Florida, in the southeastern United States.

The tiger mosquito can also spread chikungunya, a debilitating disease that causes extreme joint pain and fever. The illness is spread as well by an African mosquito, which is also expanding its range.  Professor Laura Harrington is an insect specialist at Cornell University. She says it’s not just the mosquitoes’ range that’s changing:

“We’re also seeing changes, particularly with the viruses; we’re seeing changes in their genetic material which often can lead to increased virulence,” Harrington noted.

On top of that, mosquitoes can arrive in new destinations aboard planes and in cars.

“It’s a virus that has the ability to travel on airplanes and in infected people very readily,” Weaver added.

Weaver is working on a vaccine for chikungunya that has successfully protected lab mice from getting the virus. At Cornell, Harrington is working to make the male mosquito infertile.

“The idea is that these modified males that don’t take a blood meal could be released, mate with the wild females, the females wouldn’t reproduce, they wouldn’t take a blood meal, and the population would be eliminated or reduced,” Harrington explained.

Both scientists are concerned that if a way to control the spread of chikungunya and dengue fever is not found soon, both diseases will become established in the United States. Harrington says that techniques that prove successful against these illnesses might also be used to break the cycle of other mosquito-borne diseases, including malaria.

Source: VOA

Screening Mosquito House Entry Points as a Potential Method for Integrated Control of Malaria

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Partial mosquito-proofing of houses with screens and ceilings has the potential to reduce indoor densities of malaria mosquitoes. We wish to measure whether it will also reduce indoor densities of vectors of neglected tropical diseases.

Methodology: The main house entry points preferred by anopheline and culicine vectors were determined through controlled experiments using specially designed experimental huts and village houses in Lupiro village, southern Tanzania. The benefit of screening different entry points (eaves, windows and doors) using PVC-coated fibre glass netting material in terms of reduced indoor densities of mosquitoes was evaluated compared to the control.

Findings: 23,027 mosquitoes were caught with CDC light traps; 77.9% (17,929) were Anopheles gambiae sensu lato, of which 66.2% were An. arabiensis and 33.8% An. gambiae sensu stricto. The remainder comprised 0.2% (50) An. funestus, 10.2% (2359) Culex spp. and 11.6% (2664) Mansonia spp. Screening eaves reduced densities of Anopheles gambiae s. l. (Relative ratio (RR) = 0.91; 95% CI = 0.84, 0.98; P = 0.01); Mansonia africana (RR = 0.43; 95% CI = 0.26, 0.76; P<0.001) and Mansonia uniformis (RR = 0.37; 95% CI = 0.25, 0.56; P<0.001) but not Culex quinquefasciatus, Cx. univittatus or Cx. theileri. Numbers of these species were reduced by screening windows and doors but this was not significant.

Significance: This study confirms that across Africa, screening eaves protects households against important mosquito vectors of filariasis, Rift Valley Fever and O’Nyong nyong as well as malaria. While full house screening is required to exclude Culex species mosquitoes, screening of eaves alone or fitting ceilings has considerable potential for integrated control of other vectors of filariasis, arbovirus and malaria.

Author Summary: Mosquito vectors that transmit filariasis and several arboviruses such as Rift Valley Fever, Chikungunya and O’Nyong nyong as well as malaria co-occur across tropical Africa. These diseases are co-endemic in most rural African countries where they are transmitted by the same mosquito vectors. The only control measure currently in widespread use is mass drug administration for filariasis. In this study, we used controlled experiments to evaluate the benefit of screening the main mosquito entry points into houses, namely, eaves, windows and doors.

This study aims to illustrate the potential of screening specific house openings with the intention of preventing endophagic mosquitoes from entering houses and thus reducing contact between humans and vectors of neglected tropical diseases. This study confirms that while full house screening is effective for reducing indoor densities of Culex spp. mosquitoes, screening of eaves alone has a great potential for integrated control of neglected tropical diseases and malaria.

Citation: Ogoma SB, Lweitoijera DW, Ngonyani H, Furer B, Russell TL, et al. (2010) Screening Mosquito House Entry Points as a Potential Method for Integrated Control of Endophagic Filariasis, Arbovirus and Malaria Vectors. PLoS Negl Trop Dis 4(8): e773. doi:10.1371/journal.pntd.0000773

Editor: Neal D. E. Alexander, London School of Hygiene and Tropical Medicine, United Kingdom

Funding: SBO was supported by a scholarship kindly provided by Valent Bioscience Corporation. This study was also supported by the Centers for Disease Control and Prevention and the United States Agency for International Development through the U.S. President’s Malaria Initiative (Award Number 621-A-00-08-0007-00), the Addessium Foundation (Reenwijk, The Netherlands) and a Research Career Development Fellowship (076806) provided to GFK by the Wellcome Trust. The funders of this study had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Copyright: © 2010 Ogoma et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

More information: Full text: Screening Mosquito House Entry Points as a Potential Method for Integrated Control of Endophagic Filariasis, Arbovirus and Malaria Vectors (PDF)