Friday, November 06, 2015

WHO WER: Zika Virus Outbreaks In the Americas


Credit PAHO


# 10,695


Although it is not as well known as some of its arboviral cousins  - West Nile Virus, Dengue, and Chikungunya – the Zika Virus (ZIKV) is the latest in a series of mosquito-borne threats showing up in recent years in the Americas. Much like Chikungunya, Zika was – until fairly recently – only a threat in southern Africa.


Both viruses made major geographic strides in the middle the last decade, with Chikungunya jumping to Reunion Island in the Indian Ocean (before moving on to India & South East Asia) in 2005, and Zika showing up in the South Pacific in 2007.  


While not moving with the same speed as Chikungunya or Dengue, ZIKV has continued to expand its range, reaching the Americas in early 2014, just a few months after CHKV.


Zika Fever, which is spread by the Aedes Mosquito, had generally been regarded as a `mild’ disease  - at least until it sparked an unusual outbreak (along with with Dengue co-infection) resulting in a high number of neurological complications last December-February (see Zika, Dengue & Unusual Rates Of Guillain Barre Syndrome In French Polynesia).


In early March, the journal Eurosurveillance carried a Rapid Communications on  Zika Virus Infection Complicated By Guillain-Barré Syndrome.  While the exact link between ZIKAV (and/or Dengue) and GBS was undetermined, this region has reported a 20-fold increase in the neurological disorder during the recent epidemic.


Another unusual aspect with the Zika virus is that in 2011, the EID Journal carried a Dispatch on the first Probable Non–Vector-borne Transmission of Zika Virus, Colorado, USA, involving two researchers infected in Africa, one of whom returned to the Untied States and passed the virus (presumably via sexual contact) to his wife. 


Today the World Health Organization’s  WER (Weekly Epidemiological Record) carries a brief report warning of the potential for seeing this virus spread further – not only in the Americas – but anywhere suitable vectors are found.  After which, I’ll return with a bit more.


Zika virus outbreaks in the Americas

6 November 2015, vol. 90, 45 (pp. 609–616)


Until 2007, Zika virus (ZIKV) was described as causing only sporadic human infections in Africa and Asia. In 2007, an outbreak was reported from the Federated States of Micronesia (Yap), marking the first detec­tion of ZIKV beyond Africa and Asia. The emergence of ZIKV outside its previously known geographic range prompted aware­ness of the potential for the virus to spread to other Pacific islands. Since then, it has spread to French Polynesia, New Caledonia, Cook Islands, Easter Island (Chile), and subsequently to Brazil and Colombia.

ZIKV is an emerging mosquito-borne Flavivirus related to dengue, yellow fever, Japanese encephalitis, and West Nile viruses, and is transmitted by Aedes spp. mosquitoes. It was first isolated in Uganda in 1947 in rhesus monkeys from the Zika Forest and was first reported in humans in 1952.

Following the bite of an infected mosquito, symptoms may appear after an incubation period of a few days. Symptoms can last for up to a week, with a clinical presenta­tion similar to that of other arbovirus infections such as chikungunya and dengue, including fever, headache, malaise, arthralgia, myalgia, maculopapular rashes, and conjunctivitis.

ZIKV had not been known to cause severe disease until an outbreak in French Poly­nesia in 2013–2014, when there were reports of neurological and auto-immune complications, such as Guillain-Barre syndrome in the context of co-circulating arboviruses (chikungunya and dengue).

Zika virus in the Americas

Autochthonous circulation of ZIKV has been detected in the Americas since 2014. In February 2014, the national authorities of Chile confirmed the first case of autoch­thonous transmission of ZIKV in Easter Island located in the south-eastern Pacific Ocean.

In May 2015, the Ministry of Health of Brazil confirmed autochthonous transmission of ZIKV in the north-east­ern part of the country. This was the first documented outbreak in Brazil and in the Americas. As of October 2015, 14 states have confirmed autochthonous virus transmission: Alagoas, Bahia, Ceará, Maranhão, Mato Grosso, Pará, Paraíba, Paraná, Pernambuco, Piauí, Rio de Janeiro, Rio Grande do Norte, Roraima, and São Paulo.

In October 2015, the Ministry of Health of Colombia reported the first autochthonous case of ZIKV infection in the Department of Bolivar. As of 16 October 2015, ZIKV was laboratory confirmed in 9 of 98 samples from Bolivar.

Recent outbreaks of ZIKV infection in different regions of the world underscore the potential for the virus to spread further in the Americas and beyond, wherever the vector is present. Given the worldwide spread of chikungunya and dengue, associated with urbanization and globalization, there is a potential risk of outbreaks of urban ZIKV infection in urban settings in any part of the world where the mosquito vector is present or may become established in future.

WHO encourages countries at risk to:

  • strengthen laboratory capacity to confirm cases of ZIKV infection as clinical diagnosis is unreliable due to the clinical similarity of ZIKV and other arbovirus infections;
  • establish a surveillance system for the detection of neurologic and auto-immune complications;
  • implement social communication strategies to engage the community in reducing the population of the mosquito vectors


While ZIKV hasn’t taken off the way that CHKV has in the Caribbean & South America (> 1.5 Million cases), or WNV in North America, it has shown the ability to spread rapidly in other regions of the world and the assumption is it could do the same in the Americas at some point.

The vector for ZIKV is the same as for Chikungunya and Dengue – the Aedes mosquito – and two species (Aedes Aegypti & Aedes Albopictus) are well distributed in the Southern United States.


Credit CDC


Although ZIKV hasn’t shown up in the United States yet, the CDC maintains a Zika Virus home page, with a number of resource links, and advice on how travelers to endemic regions can protect themselves.


NOTE: Today’s WHO WER also carries an in-depth report on:

Malaria situation, 2015
Based on updated WHO Fact Sheet, October 2015

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