Anopheles gambiae mosquitoes are the main transmitters of malaria, which affects around 200 million people every year. The females mate only once during their lives.
They store the sperm from this single mating in an organ called the spermatheca, from which they repeatedly take sperm over the course of their lifetime to fertilise the eggs that they lay. The female needs the sperm to stay healthy whilst they are in storage in the spermatheca, so that they are viable each time she uses them to reproduce.
The new research shows that the sperm are partly protected by the actions of an enzyme called HPX15. When the researchers interfered with HPX15 in female A gambiae mosquitoes in the laboratory, the females fertilised fewer eggs and therefore produced fewer offspring. This is the first time that scientists have discovered a mechanism that preserves the function of sperm in A gambiae.
The researchers, from Harvard School of Public Health, the University of Perugia and Imperial College London, believe that their insight could ultimately lead to a new weapon in the fight against malaria. This would work by disabling HPX15 to reduce female fertility and through that, reduce the number of malaria-carrying mosquitoes in circulation.
“Malaria kills over 650,000 people every year and we need to find new ways of tackling it, partly because mosquitoes continue to evolve ways of resisting our efforts,” Dr Robert Shaw, one of the lead authors of the research, said. “We are interested in cutting the numbers of malarial mosquitoes by impairing their ability to reproduce, and our new study suggests a way that we might be able to do this.
“There is no single magic bullet for tackling malaria, but making mosquitoes less fertile could provide us with a valuable weapon against the disease,” said Shaw. The study suggests that HPX15 may protect the stored sperm against potentially damaging molecules called free radicals, which are particularly abundant after a female takes a blood feed.
Ensuring that the sperm are healthy after blood-feeding is important for the female’s fertility as she reproduces after each feed, fertilising her eggs with sperm released from the spermatheca. The study was published in the journal Proceedings of the National Academy of Sciences.
India has recorded 15,983 dengue cases so far in 2013 as compared to 8,899 cases in the corresponding months last year, latest health ministry data shows. But the good news is, while the cases have risen sharply, fatalities have actually declined – 56 as compared to 76 last year.
Kerala reported most dengue cases at 5,801, followed by Karnataka (3,775), Tamil Nadu (3079) and Maharashtra (961) till end-July . Delhi witnessed a sharp rise in cases over the last few weeks, with the total this year touching 54. No one has died due to dengue in the capital so far.
‘Several factors for spread of dengue’
“There is no single reason for the increase in dengue cases. It is governed by various man-made and environmental factors including unprecedented growth in population, unplanned and rapid urbanization and inadequate waste management,” union health minister Ghulam Nabi Azad stated in a written reply in the Lok Sabha on Tuesday.
Increasing mobility of the population and poor infrastructure to monitor mosquito breeding were some other reasons cited by the health minister. Azad said guidelines for clinical management of dengue cases have been sent to the states for circulation in hospitals and rapid response teams have been formed.
Dengue, termed by many experts as the world’s most rapidly spreading mosquito-borne viral disease, is caused by four serotypes . While type I and III are milder in nature causing classic dengue fever and fever without shock, respectively, dengue type II and IV are considered deadly. These cause fever, bleeding and a drop in platelet count. Researchers say severe dengue cases, dengue hemorrhagic fever and dengue shock syndrome, started showing up in India since 1988.
“A reason behind the increased frequency could be the presence of many strains of the virus. It exposes people already infected to become susceptible to infection as they are not immune to all the subtypes,” said Dr Ekta Gupta, clinical virologist at the Institute of Liver and Biliary Sciences (ILBS).
Experts say construction sites are a major area of mosquito-breeding followed by government buildings and water tanks. “In Mumbai, the municipal body, charges heavy fines if mosquitoes are found to be breeding at a site. The building’s completion certificate is stalled till the fine is paid. Similar steps should be taken in cities like Delhi,” said Dr Jagdish Prasad, director general of health services.