In December’s edition of Epi-Insight, HPSC reported on the emergence of Zika virus infection – an emerging mosquito-borne infection - and associated clusters of congenital skull and brain abnormalities, in a number of countries in the Americas and the Caribbean (Volume 16 Issue 12), noting that the European Centre for Disease Prevention and Control (ECDC), the HSE and HPSC were advising women who are pregnant or who might become pregnant to make every effort to protect themselves against biting mosquitoes while travelling in areas affected by Zika virus infection. Since then, Zika virus infections have been reported in an increasing number of countries.1 The following countries have reported local transmission of confirmed Zika virus infections in past nine months:
Barbados, Bolivia, Brazil, Cape Verde, Colombia, Costa Rica, Curacao, Dominican Republic, Ecuador, El Salvador, Fiji, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Maldives, Martinique, Mexico, New Caledonia, Nicaragua, Panama, Paraguay, Puerto Rico, Saint Martin, Samoa, Solomon Islands, St Croix US Virgin Islands, Suriname, Thailand, Venezuela.
Brazil has been particularly affected by this recent upsurge. In November 2015, Brazilian authorities reported an extensive, evolving outbreak of Zika virus infection in Brazil with tens, (possibly hundreds) of thousands of cases of Zika virus infection in north-eastern Brazil. From 22 October 2015 until 9 January 2016, Brazilian health authorities have reported more than three thousand suspected cases of congenital microcephaly that meet the definition in the epidemiological surveillance protocol issued by the Brazilian Ministry of Health.2 Of these infants, 49 have died.3
There have been almost 4,000 suspected cases of microcephaly associated with any infectious agent since 22 October 2015. Of these, 49 cases have died. Two hundred and twenty four (224) cases of microcephaly have been confirmed.
ECDC has produced a map showing which countries have local Zika virus infection transmission.
Zika Virus infection
Zika virus infection is a febrile illness caused by the Zika virus, a flavivirus from the Flaviviridae family. It is transmitted by the bite of mosquitoes infected with Zika virus, generally mosquitoes from the Aedes genus (primarily Aedes aegypti).
Zika infection produces a clinical syndrome similar to, but milder than dengue fever. Zika virus is related to dengue, yellow fever, West Nile and Japanese encephalitis virus. Zika virus infection typically presents with fever, headache, maculopapular rash, followed by conjunctivitis and arthralgia. There is some evidence that Zika virus can be transmitted through direct, human-to-human contact, possibly sexual contact, and can, extremely rarely, exhibit haemorrhagic manifestations. As many as 80% of cases are asymptomatic.2
There is increasing evidence that infection with Zika virus during pregnancy can result in foetal microcephaly;2 cases of this disorder have been reported from Brazil and French Polynesia. In December, it was reported3 that more than 700 cases of microcephaly had been identified over a three month period in Brazil (which compared with about 150 cases annually for the entire country in previous years). As of 9/1/2016, the number of Brazilian cases of microcephaly had increased to 3,530 suspected cases. Among the confirmed microcephaly cases, six have been confirmed as being associated with Zika virus infection.
Zika Virus-carrying mosquitoes
Currently, Zika virus is primarily transmitted by the more tropical form of the Aedes mosquito – Aedes aegypti. Aedes mosquitoes are a tropical and subtropical genus of biting mosquito and carry a range of diseases (mainly flaviviral): dengue fever, yellow fever, West Nile fever, eastern equine encephalitis and more recently, chikungunya (an alphavirus) and Zika virus. Aedes mosquitoes tend only to be active and to bite during the day time (unlike most other mosquito species)1 - They are especially active in the morning and later afternoon. There are two major (and several minor) Aedes species: A. albopictus (the ‘Tiger’ mosquito) and A. aegypti (the ‘yellow fever’ mosquito).
A. aegypti: is the principal vector for dengue fever, yellow fever and - currently - Zika virus but it can also transmit chikungunya. A. aegypti is slightly more temperature and moisture sensitive than A. albopictus and although is found in tropical areas only now, was as recently as the 19th century, found in central Europe (the reasons behind its disappearance from such temperate areas is unknown). A. aegypti has recently been reported sporadically from countries bordering the Mediterranean and Black Sea.
A. albopictus: while the principal vector for chikungunya virus, can also transmit yellow fever virus and dengue fever. A. albopictus is hardier than A. aegypti and has a wider geographical area of distribution. As a result, A. albopictus is currently found in both tropical and subtropical/temperate parts of the world. In Europe, A. albopictus has been identified in a range of European countries;5 primarily bordering the Mediterranean but also as far north as the Balkans, Germany and Switzerland. A. albopictus is an aggressive species and can withstand lower temperatures and moisture levels than A. aegypti. In addition, although albopictus has not been, to any great extent, associated with Zika virus transmission, it is a suitable vector for Zika virus.
It is possible that A. albopictus may, in the future, become a vector for Zika virus.
Prevention of mosquito bites is the most effective way of controlling Zika virus (or any mosquito-borne) infection, as there is neither a vaccine nor prophylactic/therapeutic medication available to prevent the development of Zika virus infection. As a result, it is imperative that people who travel to affected areas are aware of:
A) The types of transmitting mosquitoes as the different species will have different geographical distributions, and can bite (and therefore increase a person’s risk) at different times of day and
B) The necessary steps to be taken to prevent mosquito bites.
Travel to Affected Areas
On 15/1/2016, the US Centers for Disease Control and Prevention issued a travel alert urging women who are pregnant or who are trying to become pregnant to postpone travelling to countries where there is ongoing transmission of Zika virus. CDC went on to advise that women whose travel to any affected areas was necessary, should consult their healthcare provider prior to travel and follow strict guidelines to avoid mosquito bites during their trip. This alert followed closely on a similar alert from PAHO (WHO-Pacific Region) on 5/1/2016.
In December, HSE and HPSC advised women who are pregnant or who might become pregnant to be aware of the risk of Zika virus and microcephaly and to make every effort to protect themselves against biting mosquitoes while travelling in areas affected by Zika virus illness (which corresponds very closely with malarious areas in the world).
On 20/1/2016, the European Centre for Disease Prevention and Control issued an updated Rapid Risk Assessment (RRA) (1st Update). The RRA concluded:
The spread of Zika virus in the Americas is likely to continue as Aedes aegypti and Aedes albopictus are widely distributed. There is a significant increase in the number of babies born with microcephaly in the north-eastern states of Brazil, however, the magnitude and geographical spread of the increase have not yet been well characterised. Despite growing evidence of a link between intra-uterine Zika virus infection and adverse pregnancy outcomes, a causal link between these events has not yet been confirmed.
As neither treatment nor vaccines are available, prevention is based on personal protection measures similar to the measures that are applied against dengue and chikungunya infections.
ECDC has advised that the following options should be considered:
- Advise all travellers to affected areas to take individual protective measures to prevent mosquito bites.
- Advise travellers that have immune disorders or severe chronic illnesses to consult their doctor or seek advice from a travel clinic before travelling.
- Advise pregnant women and women who are trying to become pregnant, and who plan travel to the areas experiencing transmission of Zika virus, to discuss their travel plans with their healthcare providers and to consider postponing their travel to affected areas, especially to areas with increasing or widespread transmission.
- Advise EU citizens who live in areas with Zika virus transmission to take individual protective measures to prevent mosquito bites. This applies particularly for pregnant women and women who are trying to become pregnant living in areas with increasing or widespread transmission.
- Individual protective measures to prevent mosquito bites should be applied all day long, especially during mid-morning and late afternoon to dusk, which are the periods of highest mosquito activity.
- Personal protection measures to avoid mosquito bites should include:
- Using mosquito repellents in accordance with the instructions indicated on the product label. DEET®-based repellent use is not recommended in children under three months of age.
- Wearing long-sleeved shirts and long pants, especially during the hours of highest mosquito activity.
- Using mosquito nets, impregnated or not, is essential if accommodations are not adequately screened or air-conditioned.
- Travellers showing symptoms compatible with dengue, chikungunya or Zika virus disease within three weeks after returning from an affected area should contact their healthcare provider.
- Pregnant women who have travelled to areas with Zika virus transmission should mention their travel during antenatal visits in order to be assessed and monitored appropriately.
HPSC endorses these recommendations.
The Department of Foreign Affairs and Trade has issued travel advice to reflect these recommendations.
The ECDC website has updated information on affected countries.
Paul McKeown, HPSC
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