Killing mosquitoes, fewer mosquitoes may increase dengue fever
A research study in Thailand found that the killing off of mosquitos may increase dengue fever.
Yoshiro Nagao and other researchers of the London School of Hygiene and Tropical Medicine say that dengue, which is also known as ‘breakbone fever’, dengue is usually not fatal for the first time around. Researchers say that the real threat is the second infection of dengue.
According to Yoshiro Nagao of the London School, there are 4 varieties of the dengue infection, which are scientifically known as serotypes.
Yoshiro Nagao says if a person is bitten by a mosquito carrying serotype A and then a year later by one carrying serotype B, the antibodies made in response to virus A would bind to the virus B but not destroy dengue.
They say that such pairs instead over-stimulate the immune system, causing a potentially fatal disease called dengue haemorrhagic fever ‘DHF.’
Nagao says that for a few weeks after a person contracts dengue, one has a kind of immunity that destroys other dengue serotypes.
Just in case a person gets serotype B during such weeks, a person will not develop dengue, but will develop antibodies to both A and B.
Yoshiro Nagao also says that if a person gets infected by all the dengue serotypes during the period of cross-immunity, the infested person will develop antibodies to all of the dengue serotypes. Nagao says that people are more likely to catch another dengue serotype during the brief cross-immunity period when there are many of mosquitoes around.
Researchers also said that fewer mosquitoes would lessen the frequency of dengue infections and people would be less likely to catch another dengue serotype during the crucial window.
Researchers tested their hypothesis by combining the incidence of dengue in Thailand with a huge Thai survey that sampled water containers in a million homes in Thailand from 2002 to 2004, looking for larvae of the dengue-carrying Aedes mosquito. They found that as mosquito dengue infection rates climbed towards 30% of houses, dengue DHF cases also increased.
However, once over the 30%, the relationship was reversed, and dengue cases dropped off as dengue infection rates climbed, 70% of homes in some villages had Aedes larvae, and that a mathematical model based on the survey showed that cutting this to 30 per cent would increase dengue DHF cases by more than 40%. Dengue researchers warned that dengue infestation needed to be reduced to less than 10% to reduce dengue DHF cases, but achieving such an extensive reduction might be difficult.
Nagao says that since measures to control mosquito population, such as spraying insecticide, may increase the number of dengue DHF cases, such measures should be “subject to ethical discussion”.
An article on the research has been published in the journal PLoS Neglected Tropical Diseases.
Killing mosquitoes may increase dengue fever
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