A method of testing
mosquitoes is in line to become a powerful tool in ascertaining the success of Filarial
elimination in the country.
In the conventional setup, scientists collect data
about number of infected patients before and after an elimination drive. This
is achieved by testing for filarial worm infection in human blood samples. This
is expensive, labor-intensive, and invasive, as it requires skilled clinicians
to draw blood under hospital settings. Fortunately now, scientists have a new
non-invasive method of finding filarial parasite in mosquitoes that can help
them accomplish this goal at lower cost, lesser time, and with high efficiency.
In a recent study in Tamil Nadu, scientists looked for
infected mosquitoes rather than looking for infected humans. This technique called
Molecular Xenomonitoring was previously successful in Sri Lanka
in the year 2006, and has now shown promise in India. “Molecular Xenomonitoring is the detection of parasite DNA or RNA in mosquitoes
and can serve as an alternative method for estimating the infection prevalence
in human populations”, say scientists.
The study was done by Vector Control Research Centre
(Indian Council of Medical Research), Puducherry, India; Neglected Tropical
Diseases Support Center, Task Force for Global Health, Georgia, USA; Department
of Public Health, Government of Tamil Nadu, India; SJL Global Consulting,
Seattle, Washington, USA; and the Department of Biological Sciences, Smith
College, Massachusetts, USA. They published their results in a recent issue of
the journal PLOS Neglected TropicalDiseases.
Lymphatic filariasis affects 947 million people globally,
of which one third of the disease burden is in India. As per our commitment to
WHO, filariasis has to be eliminated by year 2020. To achieve this goal, many
districts have undergone 10-12 rounds of mass drug administration, of which 72
districts have achieved success, and 147 districts are undergoing the process.
Lymphatic Filariasis, commonly called Elephantiasis
causes thickening and swelling of limbs, genitals, and breasts. It is
accompanied by sub-optimal mental health and social stigma. After the filarial
roundworm enters a patient’s body, it remains in the body for up to 8 years,
blocks vessels and brings down the immune system. Worms produce numerous larvae
in the body that are spread to other humans by mosquitoes.
Mosquitoes were
collected from two locations- Thanjavur and Ammapettai districts in Tamil Nadu. Both these
locations are known hotspots of filariasis. Mosquitoes were trapped in gravid traps kept outside 207 houses
in the evening. Next morning, the mosquitoes were brought to the lab, where
they were tested for the presence of the filarial parasite. The exercise was done
in the year 2000 and then followed up in 2012, to determine if elimination
drive was successful. The number of infected mosquitoes reduced from 2.7% to
1.2%, which matched the reduction in infected patients from 49.5% to 23.4%.
“Molecular xenomonitoring supported the observed filariasis infection trends
found in humans. It is a low cost, non-invasive monitoring and evaluation tool
with sensitive detection of infection signals in low prevalence settings. Owing
to poor hygienic conditions in India, high rate of mosquito breeding causes
disease resurgence. This technique can be used to monitor mosquitoes in an area
post-success also”, says Dr. Jambulingam Purushothaman, Director at the Vector
Control Research Centre, Pondicherry.
He believes that the technique will expand to other
areas and will help eliminate diseases like kala azar in the future. Presently,
three other districts in Tamil Nadu, Puducherry, and Orissa are being tested
with this technique to determine the success post-elimination drive. This
requires building regional laboratories and training manpower, which is on the agenda,
he said.
The story was published by India Science Wire.
Reference: PLOS Neglected Tropical Diseases (April
2017). doi-10.1371/journal.pntd.0005519.
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