Wednesday, 2 November 2011

Hantavirus in Andhra Pradesh: Mystery shrouds over the strain of Hantavirus infection

Syed Akbar
Hyderabad, Oct 31: The Hantavirus cases reported from Karimnagar and
Nellore districts will remain a "scientific mystery" as no virus
culture or polymerase chain reaction (PCR) tests were conducted on the
blood samples obtained from the patients.

Laboratory tests of blood samples from three patients in Nellore and
one patient from Karimnagar were limited to just identifying the
anti-Hantavirus IgM. No tests were conducted to identify the serotype
or strain of the Hantavirus. Though the disease was "clinically"
identified, it could not be reconfirmed "scientifically" as by the
time blood samples were collected from the patients, the virus had
died, leaving behind traces of antibodies.

Hantaviruses are broadly divided into two groups and as many as two
dozen strains have been identified so far. Those circulating in Asia
are different from those in the USA and other American countries.
Identification of the strain will help to understand the nature of
Hantavirus and plan medical treatment accordingly. While some
Hantaviruses cause renal failure, others attack the lungs.

When a virus or any pathogen attacks a person or animal, the body
responds to repel the attack by producing what are called antibodies.
The virus dies after a specific period. If blood samples are collected
during the period when the virus is alive, its serotype or strain can
be identified. But in all the four cases of Hantavirus infections
reported in the State, blood samples were sent for anti-Hantavirus IgM
tests only after the virus had died. Since anti-Hantavirus IgM
antibodies were noticed by the laboratories which conducted the tests,
the cases were declared as Hantavirus infection.

Dr K Ramesh, research fellow from the National Institute of
Epidemiology, Chennai, said they did not send the samples for virus
strain identification. “We diagnosed the disease through antibodies,”
he added.

Thus the strain or serotype of Hantavirus that had infected these four
persons will remain a mystery. Senior virologist Dr Yogesh K Gurav
from the National Institute of Virology, who visited Hyderabad and
other places, could not collect the blood samples from the patient as
it would not help in identification of the virus. The only way to
identify the strain is to catch infected rodents from the areas where
the patients live and analyse the blood, urine and faecal samples of
rats/mice for virus culture or PCR tests.

"We have been advised to collect blood samples from patients with
fever reporting from Karimnagar and surrounding areas. Analysis of
these samples by NIV will help in identification of the strain of the
virus. As many as 21 strains of Hantaviruses circulate in the world
and which type has caused the disease in Karimnagar patient will be
known only after a through analysis," said Dr MV Rao, senior physician
in Yashoda Hospital. Dr Rao had diagnosed the Karimnagar case as that
of Hantavirus after he sent the blood samples to a lab in Mumbai for
IgM test.

Dr Veera Pratap, epidemiologist from Nellore who collected blood
samples from suspected areas, said they had not identified the strain
but doctors in a corporate hospital in Chennai, where the patients
were treated, had diagnosed the disease as one caused by Hantavirus.

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