(Reuters) - The World Health Organization (WHO) said on Thursday
the Zika virus, linked to severe birth defects in thousands of
babies in Brazil, is "spreading explosively" and may infect 3 to 4
million people in the Americas, including 1.5 million in
Brazil.
Here are some facts about the virus and the current outbreak.
- The virus is transmitted to people through the bite of infected
female Aedes mosquitoes, the same type of mosquito that spreads
dengue, chikungunya and yellow fever. Efforts to control the spread
of the virus include eliminating mosquito breeding sites and taking
precautions against mosquito bites such as using insect repellent
and mosquito nets.
- There is no treatment or vaccine available for Zika infection.
People who get Zika virus disease typically have a mild fever, skin
rash, conjunctivitis, muscle and joint pain and fatigue, with
symptoms normally lasting for two to seven days. Most people never
develop symptoms. U.S. health officials say the United States has
two potential vaccine candidates and may begin human clinical
trials by the end of 2016, but there will not be a widely available
vaccine for several years.
- The virus has been linked to a devastating birth defect called
microcephaly in which babies are born with abnormally small heads
and brains that have not developed properly. The WHO said a direct
causal relationship between Zika virus infection and birth defects
has not yet been established but is strongly suspected. Local
health authorities in Brazil in 2015 observed an increase in babies
born with microcephaly at the same time as a Zika outbreak. About
4,000 cases of microcephaly have been reported in Brazil since
September. Given an estimated 80 percent of people infected have no
symptoms, it can be hard to tell if a pregnant woman has been
infected. Research by Brazilian authorities indicates the greatest
risk of microcephaly appears to be associated with infection during
the first trimester of pregnancy.
- The WHO said Zika cases have been reported in 23 countries and
territories in the Americas in the current outbreak. Brazil has
been the nation most affected. The Pan American Health Organization
said Aedes mosquitoes are found in all countries in the Americas
except Canada and continental Chile, and the virus will likely
reach all countries and territories of the region where Aedes
mosquitoes are found.
- Zika virus is found in tropical locales with large mosquito
populations. Outbreaks of Zika virus disease have been recorded in
Africa, the Americas, Southern Asia and Western Pacific. The virus
was first identified in Uganda in 1947 in rhesus monkeys and was
first identified in people in 1952 in Uganda and Tanzania,
according to the WHO.
- One case of possible person-to-person sexual transmission has
been described but the Pan American Health Organization said more
evidence is needed to confirm whether sexual contact is a means of
Zika transmission. PAHO said there is currently no evidence the
virus can be transmitted to babies through breast milk. PAHO said
Zika can be transmitted through blood, but this is an infrequent
transmission mechanism.
- The WHO says that because no big Zika outbreaks were recorded
before 2007, little is known about complications caused by
infection. Long-term health consequences remain unclear. It is
uncertain whether in pregnant women the virus crosses the placenta
and causes microcephaly. During an outbreak of Zika from 2013-2014
in French Polynesia, national health authorities reported an
unusual increase in Guillain-Barre syndrome, a rare disorder in
which the body's immune system attacks part of the nervous system.
Health authorities in Brazil have also reported an increase in
Guillain-Barre syndrome. Other uncertainties surround the
incubation period of the virus and how Zika interacts with other
viruses that are transmitted by mosquitoes such as dengue.
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