Scientists go door to door to bring the pests in, PCR test tells them which ones are dangerous
OVER the last few years, people from some villages of Orissa got used to a team of researchers knocking on their doors at five in the morning.
The team was on a mission to collect mosquitoes to study the insects' role in the transmission of malaria in the area.
The team would enter houses and use sucking tubes to collect mosquitoes. Mosquitoes outside the houses were collected in the evening using
light traps which produce ultraviolet light to attract mosquitoes. Orissa's Boudh, Gajapati, Phulbani, Cuttak and Keonjhar were the districts roped
in for the project as they are endemic to malaria. Three Anopheles mosquito species are dominant here A annularis, A
philippinensis and A pallidus.
In one such field work, the team from the Regional Medical Research Centre (rmrc) and the Institute of Life
Sciences in Bhubaneswar, collected 186 mosquitoes. In the lab, the researchers used a newly-developed technique called the multiplex
polymerase chain reaction (pcr) to identify the mosquitoes and assess the threat they could pose.
||Step 1 Sucking tubes were used to collect mosquitoes. One end of the tube was placed over the mosquito on the wall while it was sucked in through the other end
||Mosquitoes outside the houses were collected in the evening using light traps hung on trees
Step 2 The collected mosquitoes were dissected
Step 3 Different parts of a dissected mosquito were collected
a - the saliva for the Plasmodium parasite
b - the stomach for human blood
c - the mosquito's own DNA sample
||Step 4 The samples were analyzed by the multiplex PCR device. The results confirmed if the mosquito had fed on a human and if it carried the disease
technology uses bits of dna
to identify the organism from which it has been
taken, by comparing it to standard sequences of the organism's dna
already available. The team had three
variables to identify the species of the mosquito, whether it had fed on a human host and whether the malaria pathogen (Plasmodium
) was present in its salivary glands. If the mosquito sample being analyzed showed the presence of genetic material from human
blood (in its stomach contents) as well as from the protozoan (in its salivary glands), along with its own dna,
meant the mosquito fed on human host and was a potential vector of the parasite. For comparison, separate markers from human blood and the
The common method to identify the mosquito involves catching a female about to lay eggs, right after its blood meal. The growing larvae are
studied which takes 12 days. The presence of the protozoan is ascertained by visually examining cells from the mosquito's salivary glands; the
methods are cumbersome. Not only does one multiplex pcr
test take care of all these parameters, it is less
time-consuming and more accurate, said S antanu Kar, director of rmrc
and a team member.
Out of the 186 mosquitoes, 91 were A annularis
, two of which were positive for P falciparum
and one fed on a human. The 56
and 39 A pallidus
did not carry the parasite. One A philippinensis
fed on a human.
"Any malaria control strategy has to consider aspects like distribution and identification of the vectors and their host preferences besides their
susceptibility to insecticides. Now all this will be easy," said Rupenangshu Hazra, a team member. Details of the technology are to be published
in the coming issue of Transactions of the Royal Society of Tropical Medicine and Hygiene.
Kar said government employees should be trained to collect mosquitoes from every nook and corner of the state. The multiplex pcr
tests done on the collected samples could be used to carry out surveys on mosquito populations throughout the
We are a voice to you; you have been a support to us. Together we build journalism that is independent, credible and fearless. You can further help us by making a donation. This will mean a lot for our ability to bring you news, perspectives and analysis from the ground so that we can make change together.