SUNDAY 1ST FEBRUARY, 2015 – UWI TODAY
15
“Inthe initial stages,
the symptomsofmanyviral illnesses
look very similar,” says Professor Christine Carrington, “as
the disease progresses you can sometimes differentiate
them, but to confirm, laboratory testing is necessary and
the right test has to be done at the right time”.
She was explaining why a person who has all the
symptoms of Chikungunya might get a negative test
result.
“It might indeed be ChikV, but the timing of the testing
meant it was not detected, or it could be another virus
that presents similarly.”
Carrington is Professor of Molecular Genetics andVirology
and is also well known for her work on the Dengue virus.
In her office at the Department of Pre-Clinical Sciences of
The UWI’s Faculty of Medical Sciences, she and two of her
PhD students are clearing away some of the ambiguities
in my mind.
My question had to do with the fact that many doctors
appear to be unwilling to confirmwhether or not patients
carrying all the symptoms of Chikungunya actually have
the virus when lab results are negative. Trinidad and
Tobago’s Health Minister, Fuad Khan had announced
that there was a virus bearing the same symptoms and
needing the same treatment. It confused many people
who wondered about the origin of this parallel virus,
and rumours abounded that it was actually one that was
maliciously introduced into the Caribbean by forces with
secret agendas (like destroying athletes, ruining tourism,
and other dastardly plots).
So was it really two viruses? The State’s Principal Medical
Officer, Dr Clive Tilluckdharry (who is also head of the
Insect Vector Control Division at the Ministry of Health)
ventured that it was not, and the tests were possibly not
as sensitive as they should be; but he was unwilling to
say much more. Many doctors agree, but to be on the
safe side, most would rather not confirm a case if the test
would not do it.
“The laboratory tests,” says Professor Carrington as she
begins to sketch a timeline of infection showing how
virus levels increase and then decline, and the antibody
immune response that follows, “detect either the virus
(which lasts only a few days) or they detect antibodies
that the body makes in response to the infection. If you
do a virus test too late or an antibody test too early, you
can get a false negative result.”
She answers questions about the types of tests available,
other viruses that cause similar symptoms and the fact
that the treatments for many are exactly the same: “pain
killers, fever reducers, lots of fluids and rest.”
“The good news is that you can’t be re-infected with
ChikV; unlike Dengue, which you can get four times. The
joint pain can persist and re-occur for months, but it is
not a new infection.”
She and her students have been investigating the virus
itself, looking at its genetic material, evolution and the
patterns of spread. Given the “naïve population” lacking
in immunity because of the newness of the virus to the
region, which is how Dr James Hospedales, Executive
Director of the Caribbean Public Health Agency, has
described our circumstance, it is vital work, because there
are other viruses planning their Caribbean vacations and
ready to book flights.
“It’s the first wave,” says Dr Tilluckdharry ominously.
Anushka Ramjag, one of Professor Carrington’s PhD
students, is collaborating with researchers in San
Francisco to characterise immune responses to ChikV.
Another student, Nikita Sahadeo has been screening
people presenting with febrile illness at EWMSC for the
past year, and through that screening has detected and
recovered Chikungunya virus from several cases. They
are so invested in their work that they even joked about
hoping to get ChikV themselves in order to experience
it first-hand and to become readily available supplies of
the virus for their studies!
Their lab at UWI is equipped to carry out very sensitive
tests, but they have been coming at it from a research
perspective, not for diagnostic purposes, and out there
on the ground, the diagnostic labs are largely unprepared
for the kind of testing ChikV requires. Private labs, says Dr
Hospedales, are not capable of doing definitive testing. It
is why there are somany“probable”and“suspected”cases
rather than “confirmed.”
And it is a regional inadequacy; CARPHA being the only
really reliable source of diagnostic testing.
Dr Earl Marshall, who has been running a general practice
in Brown’s Town, a rural community in north Jamaica, for
many years, says that as aGP it has been stressful toget lab
confirmation. He explained the process to me by email.
“The standard lab test involves taking an acute serum at
onset of presentation and a convalescent sample 14 days
later to show a four-fold rise in titres. That therefore costs
the patients between Ja$5000 to Ja$7000 and the results
would be available about one month (rural office) after
presentation. The fever from ChikV lasts about five days
so not many patients did the convalescent sample.”
“So then we got a rapid serological test done on whole
blood in the office. Cost to the patient Ja$1500. Trouble is
the IgMantibodies are detectable five days after cessation
of the fever. IgG antibodies take another 14 days to
become detectable sonot helpful.This test was not widely
used. The manufacturers claim98% sensitivity but that is
questionable and literature suggests it could give false
positives with other alphavirus infections.”
He said that most labs claimed to be able to do the
needed tests but most doctors outside of the city made
clinical diagnoses.“Most of usmade a clinical presumptive
How can you
tell for sure?
Tests are not always reliable, say doctors
By Vaneisa Baksh
Several methods can be used
for diagnosis.
Serological tests, such as enzyme-linked
immunosorbent assays (ELISA), may confirm
the presence of IgM and IgG anti-chikungunya
antibodies. IgMantibody levels are highest three
to five weeks after the onset of illness and persist
for about twomonths. Samples collected during
the first week after the onset of symptoms should
be tested by both serological and virological
methods (RT-PCR).
The virus may be isolated from the blood
during the first few days of infection. Various
reverse transcriptase–polymerase chain reaction
(RT–PCR)methods are availablebut areof variable
sensitivity. Some are suited to clinical diagnosis.
RT–PCR products from clinical samples may also
be used for genotyping of the virus, allowing
comparisons with virus samples from various
geographical sources.
Source: World Health Organisation
ChikV
Testing
diagnosis based on the triad of fever, rash and arthritis in
the epidemic setting.
Dr Marshall mentioned a workshop held in early January
by the association of general practitioners which dealt
with managing febrile conditions.
“The discussion period highlighted our ignorance of
the ChikV infection, especially regarding the long term
arthritis that seems to affect 60 to 70% of patients. This
we learned can lead to long term cartilage and joint
destruction with resulting deformity, so in many ways it
looks like rheumatoid arthritis.”
He said it was difficult to ascertain the impact of ChikV
generally.
“Most of my patients work hard physically, primarily as
labour intensive farmers. ChikV, with the chronic joint
inflammation that flares with vigorous physical activity
should have a really bad effect here economically. The
problem is the most affected would not be able to afford
my services.”
The
Chikungunya
Effect
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