Controlling dengue

Credit: CORBIS

An open field trial in Australia has revealed that infecting mosquitoes with the endosymbiotic bacterium Wolbachia pipientis str. wMel has great potential to control the spread of dengue virus (DENV). Spread by the mosquito Aedes aegypti, DENV infects up to 50 million people worldwide each year and results in around 12,500 deaths. Previous work had indicated that it might be possible to control A. aegypti populations by infecting them with W. pipientis str. wMelPop-CLA, as this strain reduces the lifespan of the infected mosquito, thereby decreasing the potential of transmitting DENV. Unfortunately, the shortened lifespan also affected the ability of mosquitoes to pass on the bacterium to subsequent generations, hampering the use of this strain as a control agent. Two studies now reveal that using the avirulent wMel strain to infect mosquitoes has little effect on lifespan, reproductive rates and offspring viability. In an open field trial, 300,000 wMel-infected adult mosquitoes were released into wild populations of A. aegypti in two remote areas of Australia. The bacteria spread rapidly through the population at both sites and after 5 weeks were found in nearly all mosquitoes tested. Furthermore, infection of female mosquitoes seems to block DENV transmission, although the mechanism behind this remains unclear. Nature/Washington Post/Science

Mapping the spread of cholera

Molecular epidemiological studies have identified at least three waves in the current Vibrio cholerae pandemic. Throughout history, there have been seven acknowledged cholera outbreaks, with the V. cholerae 'classical' biotype responsible for the first six and the 'El Tor' biotype responsible for the seventh, ongoing pandemic. A team from the Sanger Institute, UK, has mapped single-nucleotide polymorphisms in 154 whole genome sequences of V. cholerae isolates from around the world to show that the current pandemic spread from the Bay of Bengal in at least three independent, overlapping waves with a common ancestor in the 1950s.

A separate study has used whole-genome sequence typing, pulsed-field gel electrophoresis and antimicrobial susceptibility testing to evaluate the potential Nepalese origin for the 2010 Haitian cholera outbreak. Twenty-four V. cholerae isolates from Nepal were found to belong to a single monophyletic group that also contained isolates from Bangladesh and Haiti, supporting the idea that cholera was spread to Haiti by Nepalese soldiers working as United Nations peacekeepers in the aftermath of the 2010 earthquake. Nature/mBio/BBC

Microwaves and smelly socks

Two very distinct approaches to tackle malaria have recently received funding for further development. The first aims to use microwaves to kill the parasites while they circulate in the host bloodstream. When the malaria parasite invades a red blood cell and digests haemoglobin, the iron released is stored in the parasite's feeding vacuole as an inert crystalline pigment called hemozoin. José Stoute from Pennsylvania State University, USA, and Carmenza Spadafora from the Institute for Advanced Scientific Studies, Panama, reasoned that microwave energy can be used to heat the hemozoin crystal until the food vacuole explodes, killing the parasite. Having shown that the approach can work in principle in a Petri dish, the project has been awarded US$1 million from the Bill & Melinda Gates Foundation to see whether the technique can be applied in mice.

For the second approach, Fredros Okumu has received $775,000 from the Bill & Melinda Gates Foundation and Grand Challenges Canada to develop a toxic mosquito trap that attracts the insects using the scent of worn socks. Mosquitoes are most attracted to feet, but reproducing this scent chemically would be expensive. Instead, villagers wear cotton pads in their socks which will then be used to bait the traps. NY Times/LA Times

Infectious trigger for narcolepsy

The number of new cases of narcolepsy reported in China matches the seasonal patterns of infections such as influenza, according to a new study. Narcolepsy is an autoimmune disease that causes people to suddenly fall asleep and is thought to be caused by the death of brain cells that secrete the hormone hypocretin. Sufferers are thought to have a genetic predisposition to the condition, which may be triggered in these individuals by an environmental factor. Data collected from >900 patients with narcolepsy who were diagnosed in Beijing, China, between September 1988 and February 2011 revealed that an increase in the number of new cases occurred 5–7 months after a peak in cold and flu cases, suggesting that the response to such respiratory tract infections may trigger the onset of the condition. In 2010, an H1N1 influenza vaccine, Pandemrix, was found to be associated with a ninefold increase in the number of new narcolepsy cases in children in Finland. However, the authors found that the rate of new narcolepsy cases in Beijing increased threefold following the 2009–2010 H1N1 influenza pandemic, despite fewer than 6% of patients having received a flu vaccination. Ann. Neurol./Telegraph/Independent

Outbreak news

Ehrlichiosis. New tests have confirmed that an outbreak of ehrlichiosis that affected 25 people in Minnesota and Wisconsin, USA, in 2009 was caused not by Ehrlichia chaffeensis or Ehrlichia ewingii, the two bacterial species known to cause the disease in the United States, but by a previously unreported species currently designated Ehrlichia Wisconsin HM543746. The new species is carried by the deer tick and is most closely related to Ehrlichia muris, which is commonly found in eastern Europe and parts of Asia. Wall Street Journal/N. Engl. J. Med.

In the News was compiled with the assistance of David Ojcius, University of California, Merced, USA. David's links to infectious disease news stories can be accessed on his Twitter page (@Ojcius)..