Zika virus outbreak (2015–present)

Zika virus outbreak (2015–present)

Situation map of the outbreak as of 3 February 2016
Date	April 2015–present
Country[1][2] Confirmed autochthonous cases Last update American Samoa[3] 4 12 February 2016 Barbados[4] 7 8 February 2016 Bolivia[5] 4 29 January 2016 Brazil[6][a] (est. 1.5 million) 30 January 2016 Cape Verde[7] 7,081 17 January 2016 Colombia[6][8] 31,555 13 February 2016 Costa Rica[5] 1 29 January 2016 Curaçao[9][10] 1 31 January 2016 Dominican Republic[11] 8 27 January 2016 Ecuador[5] 33 29 January 2016 El Salvador[12] (est. 2,500) 31 January 2016 French Guiana[5] 15 29 January 2016 Guadeloupe[13] 1 21 January 2016 Guatemala[5] 68 29 January 2016 Guyana[14] 2 15 February 2016 Haiti[5] 125 29 January 2016 Honduras[15] 3,649 1 February 2016 Jamaica [16] 1 30 January 2016 Maldives[7][17] 1 7 January 2016 Martinique[5] 47 29 January 2016 Mexico[18] 50 4 February 2016 Nicaragua[19] 31 4 February 2016 Panama[20] 50 28 January 2016 Paraguay[21] 6 3 December 2015 Puerto Rico[22] 30 12 February 2016 Saint Martin[13] 1 21 January 2016 Samoa[23][24] 3 5 February 2016 Suriname[25][26] 6 13 November 2015 Thailand[23][27] 1 5 February 2016 Tonga[28] 5 4 February 2016 U.S. Virgin Islands[5] 1 29 January 2016 Venezuela[29] 5,220 10 February 2016 Total est. 1.6 million+ as of 30 January 2016 a There are 3718 cases and 38 deaths from microcephaly.[6][30]

As of early 2016, the most widespread outbreak of Zika fever, caused by the Zika virus, is ongoing primarily in the Americas. The outbreak began in April 2015 in Brazil, and subsequently spread to other countries in South America, Central America, and the Caribbean.

In January 2016, the World Health Organization (WHO) said that the virus was likely to spread throughout the majority of the Americas by the end of the year;^[31] and in February 2016, the WHO declared that the cluster of microcephaly and Guillain–Barré syndrome (GBS) cases reported in Brazil – strongly suspected to be associated with the Zika virus outbreak – was a Public Health Emergency of International Concern.^{[32][33][34][35]}

The virus is mainly spread by the Aedes aegypti mosquito, which is commonly found throughout the tropical and subtropical Americas, but also by Aedes albopictus ("Asian tiger"), which have become widespread as far north as the Great Lakes region of North America.^[36] The Zika virus can also be transmitted through sex.^[35][37]

The majority of Zika virus infections are asymptomatic, making precise estimates of the number of cases very difficult to determine.^[38] In around one in five cases, infection with Zika virus results in a minor illness known as Zika fever, which causes symptoms such as fever and a rash. However, Zika virus infection in pregnant women has a suspected link with newborn microcephaly by mother-to-child transmission^[39][40] and, in very few cases, GBS. A number of countries have issued travel warnings, and the outbreak is expected to have an impact on the tourism industry.^[35][41]

Epidemiology

The Zika virus was first isolated in 1947 in a rhesus monkey in a forest near Entebbe, Uganda.^[42] Although serologic evidence indicated additional human exposure during subsequent decades in parts of Africa and Asia,^[43] before the 2007 Yap Islands Zika virus outbreak, only 14 cases of human Zika virus disease had been documented.^[42] Brazilian researchers have suggested that Zika virus arrived in the country from French Polynesia during the 2014 FIFA World Cup tournament,^[44] based on phylogenetic DNA analysis of the virus;^[45] French researchers speculated the virus arrived shortly afterwards, in August 2014, when canoeing teams from the Zika-afflicted Cook Islands, French Polynesia, New Caledonia, and Easter Island attended the Va'a World Sprint Championships in Rio de Janeiro.^[46][47] In May 2015, Zika virus was first confirmed as the cause of an outbreak of a dengue-like disease in northern, northeastern and southeastern Brazil.^[48] In the district of Camaçari, and the neighboring city of Salvador, capital of the state of Bahia, a previously unknown disease that caused flu-like symptoms, followed by rash and arthralgia, was shown to be caused by the Zika virus by researchers from the Federal University of Bahia using the reverse transcription polymerase chain reaction (RT-PCR) technique.^[49] The virus reached Colombia in October^[50] and other countries in Latin America including the Caribbean in November and December.^[51] Confirmed cases have now been reported in most of South and Central America, and the Caribbean.^[52] In its spread from Africa and Asia to Oceania and then to the Americas, Zika followed the same pattern as chikungunya after 2004.^[53]

Cases have also been reported that were imported from South America into Europe,^[54] Canada,^[55] United States,^[56] China,^[57] and Australia.^[58]

Transmission

Adult Aedes aegypti mosquito, a vector or carrier of the Zika virus

Zika is a mosquito-borne disease and possibly a sexually transmitted infection.^[37] The resurgence of Aedes aegypti's worldwide distribution over the past 2–3 decades makes it one of the most widely distributed mosquito species.^[59] In 2015, Aedes albopictus was present in tropical, subtropical, and temperate regions of the Americas, reaching as far north as the Great Lakes of North America and, internationally, living alongside Aedes aegypti in some tropical and subtropical regions.^[36]

The Aedes aegypti mosquito usually bites in the morning and afternoon hours, and can be identified by the white stripes on its legs.^[60] The mosquito species (Aedes aegypti, mainly, and Aedes albopictus) that can spread Zika virus can also spread dengue, chikungunya, and yellow fever.^[61]

There have been reports of Zika virus transmission via sexual intercourse. In such cases, Zika virus may have been sexually transmitted from male partners ill with the disease.^[35][37][62]

Possible link to infant microcephaly and other disorders

A baby with microcephaly (left) compared to a baby with a typical head size

The Zika virus was first linked with newborn microcephaly during the Brazil Zika virus outbreak. In 2015, there were 2,782 cases of microcephaly compared with 147 in 2014 and 167 in 2013.^[63] Confirmation of many of the recent cases is pending, and it is difficult to estimate how many cases went unreported before the recent awareness of the risk of virus infections.

Brazilian president Dilma Rousseff in a videoconference about the Zika virus at the National Center for Disaster Management.

In November 2015, the Zika virus was isolated in a newborn baby from the northeastern state of Ceará, Brazil, with microcephaly and other congenital disorders. The Lancet medical journal reported in January 2016 that the Brazilian Ministry of Health had confirmed 134 cases of microcephaly "believed to be associated with Zika virus infection" with an additional 2,165 cases in 549 counties in 20 states remaining under investigation.^[35][64]

In January 2016, a baby in Oahu, Hawaii, was born with microcephaly, the first case in the United States of brain damage linked to the virus. The baby and mother tested positive for a past Zika virus infection. The mother, who had probably acquired the virus while traveling in Brazil in May 2015 during the early stages of her pregnancy, had reported her bout of Zika. She recovered before relocating to Hawaii. Her pregnancy had progressed normally, and the baby's condition was not known until birth.^[65]

A high incidence of the autoimmune disease GBS, noted in the French Polynesia outbreak, has also been found in the outbreak that began in Brazil.^[66] However, there are no laboratory confirmations of Zika virus infection in patients with GBS.^[67]

Ocular disorders in newborns have also been linked to Zika virus infection.^[68] In one study in Pernambuco state in Brazil, about 40 percent of babies with Zika-related microcephaly also had scarring of the retina with spots, or pigment alteration.^[67]

Containment and control

Diagnosis

Symptoms of Zika virus^[69]

^[70] Symptoms are similar to other flaviviruses such as dengue fever or the alphavirus that causes chikungunya,^[71] but are milder in form and usually last four to seven days. Most cases (60–80%) are asymptomatic. The main clinical symptoms in symptomatic patients are low-grade fever, conjunctivitis, transient joint pain (mainly in the smaller joints of the hands and feet) and maculopapular rash that often starts on the face and then spreads throughout the body.^[71] In general the disease symptoms are mild and short-lasting (2–7 days).

It is difficult to diagnose Zika virus infection based on clinical signs and symptoms alone due to overlaps with other arboviruses that are endemic to similar areas.^[72] The methods currently available to test for Zika antibodies cross-react with dengue antibodies. An IgM-positive result in a dengue or Zika ELISA test can only be considered indicative of a recent flavivirus infection. Plaque-reduction neutralization tests can be performed and may be specific.^[73] The Zika virus can be identified by RT-PCR in acutely ill patients.^[35]

Americas

Most countries, including Colombia, Ecuador, El Salvador and Jamaica, advised women to postpone getting pregnant until more was known about the risks.^[74][75] Plans were announced by the authorities in Rio de Janeiro, Brazil, to try to prevent the spread of the Zika virus during the 2016 Summer Olympics in Rio.^[76] The health ministry of Peru installed over 20,000 ovitraps during the 2015 dengue outbreak. The same ovitraps will be used to monitor a potential Zika outbreak in Peru's tropical regions.^[77]

Symptoms of microcephaly, linked to mothers infected by Zika virus.^[69]

Because of the "growing evidence of a link between Zika and microcephaly" the CDC issued a travel warning on 15 January 2016 advising pregnant women to consider postponing travel to Brazil as well as the following countries and territories where Zika fever had been reported: Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Suriname, Venezuela, and the Commonwealth of Puerto Rico.^[78] On 20 January 2016, the Ministry of Health of Chile published a health notice.^[79] On 22 January 2016, eight more countries were added to the list of those affected: Barbados, Bolivia, Ecuador, Guadeloupe, Saint Martin, Guyana, Cape Verde, and Samoa.^[80] The agency issued additional guidelines and suggested that women thinking about becoming pregnant consult with their physicians before traveling.^[81] Canada issued a similar travel advisory.^[76][82]

International

Agent for endemic diseases of the city of Votuporanga, São Paulo, Brazil

Governments or health agencies such as those of the United Kingdom,^[83] Ireland,^[75] Japan,^[84] South Korea,^[85] New Zealand,^[86] Malaysia,^[87] Philippines^[88] and the European Union^[76] issued travel warnings. The warnings are predicted to have an effect on the tourism industry in affected countries.^[89][90][91]

To prevent the transmission of the Zika virus, WHO recommends using insect repellent, wearing long-sleeved clothes to cover the body, and using screens and mosquito nets to exclude flying insects from dwellings or sleeping areas. It is also vital to eliminate any standing water near homes to minimize breeding areas for mosquitos. Authorities can treat larger water containers with recommended larvicides.^[92][93] Furthermore, the Centers for Disease Control and Prevention (CDC) recommends that containers holding water near homes either be sealed or scrubbed once per week, because mosquito eggs can stick to them.

On 1 February 2016, WHO declared the cluster of microcephaly cases and other neurological disorders a Public Health Emergency of International Concern,^[32] which may reduce the number of visitors to the Rio Olympics in 2016.^[94] The designation has been applied in the past to the Ebola outbreak in 2014, the outbreak of polio in Syria in 2013, and the 2009 flu pandemic.^[95] South Korea held an emergency meeting in response to the WHO declaration in 2 February 2016.^[85]

Responses

The Brazilian Army has sent more than 200,000 troops to go "house to house" in the battle against Zika-carrying mosquitoes.

In January 2016, it was announced that, in response to the Zika virus outbreak, Brazil's National Biosafety Committee approved the releases of more genetically modified Aedes aegypti mosquitoes throughout their country. Previously, in July 2015, Oxitec published results of a test in the Juazeiro region of Brazil, of so-called "self-limiting" mosquitoes, to fight dengue, Chikungunya and Zika viruses. They concluded that mosquito populations were reduced by over 90% in the test region.^[96][97][98] Male genetically modified mosquitoes mate with females in the wild and transmit a self-limiting gene that causes the resulting offspring to die before reaching adulthood and thus diminishes the local mosquito population.^[96][99]

On 1 February 2016, the WHO declared the current Zika virus outbreak an international public health emergency.^[100][101] The same day (1 February 2016) the Brazilian President released a decree that increased local and federal pest control agents access to private property required by mobilization actions for the prevention and elimination of Aedes mosquito outbreaks in the country.^[102]

Some experts have proposed to combat the spread of the Zika virus by breeding and releasing mosquitoes that have either been genetically modified to prevent them from transmitting pathogens, or that have been infected with the Wolbachia bacterium, thought to inhibit the spread of viruses.^[103] Another proposed technique consists in using radiation to sterilize male larvae so that when they mate, they produce no progeny.^[104] Male mosquitoes do not bite or spread disease.

In February, the Brazilian federal government has mobilized 60% of the Armed Forces, or about 220,000 soldiers, to warn and educate the population of 350 municipalities on how to reduce mosquitoes breeding grounds.^[105]

See also

• 2007 Yap Islands Zika virus outbreak
• Zika virus outbreak timeline

References

External links

Wikimedia Commons has media related to Zika virus outbreak in the Americas (2015-2016).

• New York Times interactive answering questions about the Zika Virus
• Viralzone: Flaviviridae