The Zika virus is adept at entrenching itself in parts of the body that are shielded from the immune system, experts fear.
The virus’s apparent ability to ‘hide’, could make it harder to fight and possibly lengthen the time frame within which it can be transmitted.
Researchers reported that Zika virus can be detected in
semen for 62 days after a person is infected, adding to evidence
of the virus’s presence in fetal brain tissue, placenta and
Their work is part of an international race to
understand the risks associated with Zika, a rapidly spreading
mosquito-borne virus thought to be linked to thousands of cases
of birth defects in Brazil.
The Zika virus could entrench itself in organs in the body, such as the eyes, testes, placenta and brain, where it can shield itself from the immune system, Dr Anthony Fauci of the National Institutes of Health warned
Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said: ‘Right now, we know it’s in the blood for a very limited
period of time, measured in a week to at most 10 days.
now, as we accumulate experience, it can be seen in the seminal
fluid. We’re not exactly sure after the infection clears, where
else it would be.
‘These are all things that need to be carefully examined in
natural history and case-control studies,’ he said.
Dr Fauci said that Zika’s persistence in the body recalled
findings during the 2014 Ebola outbreak, the worst on record.
individual patients, the highly deadly virus remained in semen
and eye fluid for months.
Zika causes only mild symptoms, and in most cases may not
result in illness at all.
Its suspected link to the birth defect
microcephaly and to neurological disorder Guillain-Barre
syndrome has generated alarm among public health officials,
though an association has not been proven.
The World Health
Organization declared Zika a global health emergency on February 1.
Several organs in the body, including the testes, the eyes,
the placenta and the brain, are ‘immune privileged’ – protected
from attacks launched by the immune system to neutralize foreign
The Zika outbreak sweeping through the Americas was declared an international emergency over ‘strong links’ between the virus and the birth defect microcephaly, where babies are born with smaller than usual heads and often severe brain damage
These sites are safeguarded from antibodies to prevent the
immune system from attacking vital tissues.
But if a virus
enters these protected sites, it is much harder to fight them
‘The virus can continue to persist and or multiply,’ said
Dr William Schaffner, an infectious disease expert at
Vanderbilt University Medical Center in Nashville. ‘The virus is
in a bubble of sorts.’
Dr Fauci said it is not entirely surprising that Zika persists
There have already been at least two reports in which
the virus was likely transmitted sexually.
What has not been
clear is for how long.
British researchers offered some clues on Friday.
letter to the journal Emerging Infectious Diseases, scientists
reported the case of a 68-year-old man who was infected with
Zika in 2014.
They detected Zika virus 62 days after the initial
infection, but they were not able to confirm whether it could
still infect another person.
Last week, researchers in Slovenia published a paper
in the New England Journal of Medicine describing a severely
brain damaged fetus from a mother who was infected with Zika in
Brazil and later terminated the pregnancy.
In an autopsy, the authors found high levels of Zika in the
brain and some evidence that the virus had been replicating.
They suggested that Zika may persist in the fetal brain because
it is an immunologically privileged site.
That is true of many other viruses, such as toxoplasmosis,
rubella, cytomegalovirus or herpes, which can also cross the
placenta and cause microcephaly, a birth defect marked by small
head size and underdeveloped brains.
The typical route of Zika transmission is after being bitten by an Aedes mosquito, pictured, which carry the virus. However, during the current outbreak there has been on report of the virus being transmitted sexually
Doctors commonly screen
pregnant women for these infections, said Dr Ian Lipkin of the
Center for Infection and Immunity at Columbia University in New
Dr Lipkin said the key concern about Zika harboring in immune
protected sites is that it could be transmitted sexually through
So far, there is little to suggest sexual transmission is
common, said Dr Eric Rubin, an infectious disease expert at the
Harvard School of Public Health, ‘but it will bear looking at so
that we can counsel individuals about the risk that they pose to
U.S. health officials advise that men who come to the
country from Zika outbreak areas should consider using condoms
even with non-pregnant sex partners because the virus may persist
in semen even after it clears the bloodstream.
‘They don’t say for how long,’ Dr Schaffner said. ‘That’s
because they don’t know. As it was with Ebola, we’re learning as
ZIKA VIRUS: A TIMELINE CHARTING DISEASE’S SPREAD AROUND THE GLOBE
The following timeline charts the origin and spread of the Zika virus from its discovery in Uganda nearly 70 years ago:
1947 – Scientists researching yellow fever in Uganda’s Zika Forest isolate the virus in samples taken from a rhesus monkey
1948 – Virus recovered from Aedes africanus mosquito in the Zika forest
1952 – First human cases detected in Uganda and Tanzania
1954 – Virus found in young girl in Nigeria
1960s-1980s – Zika detected in mosquitoes and monkeys in band of countries stretching across equatorial Africa
1969-1983 – Zika is found in equatorial Asia, including India, Indonesia, Malaysia and Pakistan
2007 – Zika spreads from Africa and Asia to cause the first large outbreak in the Pacific island of Yap
2012 – Two distinct lineages of the virus, African and Asian, are identified by researchers
2013-2014 – Zika outbreaks in French Polynesia, Easter Island, the Cook Islands and New Caledonia. Retrospective analysis shows possible link to birth defects and severe neurological complications in babies in French Polynesia
March 2, 2015 – Brazil reports an illness characterised by skin rash in northeastern states
April 29, 2015 – Brazilian samples test positive for Zika
July 17, 2015 – Brazil reports detection of neurological disorders in newborns associated with history of infection
October 5, 2015 – Cape Verde reports cases of illness with skin rash
October 22, 2015 – Colombia confirms cases of Zika
October 30, 2015 – Brazil reports unusual increase in cases of microcephaly – abnormally small heads – among newborns
November 11, 2015 – Brazil declares a national public health emergency
Nov 2015-Jan 2016 – Cases reported in Suriname, Panama, El Salvador, Mexico, Guatemala, Paraguay, Venezuela, French Guiana, Martinique, Puerto Rico, Guyana, Ecuador, Barbados, Bolivia, Dominican Republic, Nicaragua, Curacao, Jamaica
February 1, 2016 – World Health Organization declares a public health emergency of international concern