Zika infection is a mild febrile viral illness transmitted by mosquitoes. A few outbreaks have been reported in tropical Africa and in some areas in Southeast Asia.

Agent

Zika virus is a mosquito-borne flavivirus closely related to dengue virus. The virus was first isolated in 1947 from a sentinel rhesus monkey stationed on a tree platform in the Zika forest, Uganda [2].

Reservoir

The virus reservoirs are presumably monkeys.

Transmission modes

Zika virus is transmitted to humans mainly by certain species of Aedes mosquitoes. Some of these species bite during the day as well as in the late afternoon/evening.

Clinical presentation

The main clinical symptoms in patients are fever, conjunctivitis, transient arthritis/arthralgia (mainly in the smaller joints of the hands and feet) and maculo-papular rash (that often starts on the face and then spreads throughout the body). In general the disease symptoms are mild and short-lasting (2-7 days). There is no evidence that Zika infection affects pregnant women or their babies. However, there are very few case reports in the literature [2][3].

Diagnosis

Zika virus can be identified by RT-PCR in acutely ill patients and from day 5 post onset of fever by serology (detection of specific IgM antibodies). Serological cross-reactions with closely related flaviviruses are possible [4][5].

Treatment

Symptomatic only (non-steroid anti-inflammatories, non-salicylic analgetics); no vaccine or preventive drug is available.

Prevention

To reduce the risk of contracting Zika virus infection - as for the other mosquito-borne infections - travellers should minimise the exposure to mosquito bites by taking the following preventive measures:

1. Use of anti-mosquito devices (insecticide-treated bed nets, coils, smudge pots, spray, repellents) and wearing long sleeves and clothes with long legs, especially during the hours of highest mosquito activity (morning and late afternoon). Mosquito repellent based on a 30% DEET concentration is recommended;
2. Before using repellents, pregnant women and children under the age of 12 years should consult a physician or pharmacist;
3. For newborn children under three months, repellents are not recommended; instead, insecticide-treated bed nets should be used.

Acknowledgement

For more information on avoiding mosquito bites, refer to http://www.nathnac.org/pro/factsheets/iba.htm published by the National Travel Health Network and Centre, NaTHNaC, in the UK.

Measures at the community level include,

1. Reduction of mosquito breeding sites (removal of all open containers with stagnant water in and round houses, or, if that is not possible, treatment with larvicides);
2. In affected areas, elimination of adult mosquitoes through aerial spraying with insecticides.
   

Outbreaks of Zika virus

Serologic studies have shown that Zika infections are occurring from Africa to Southeast Asia; in 1978 a small outbreak of acute fever in Indonesia due to Zika virus infection was described.

The most recent known outbreak has been reported on Yap Island, Federated States of Micronesia (FSM) from April to July 2007. This was the first outbreak of Zika virus identified outside of Africa and Asia. A total of 108 cases were confirmed by PCR or serology and 72 additional cases were suspected. The most common symptoms were rash, fever, arthralgia and conjunctivitis, and no deaths were reported. The mosquito Aedes hensilli , which was the predominant species identified in Yap during the outbreak, was probably the main vector of transmission. While the way of introduction of the virus on Yap Island remains uncertain, it is likely to have happened through introduction of infected mosquitoes or a viraemic human [3].

References

[1] Fagbami AH. Zika virus infections in Nigeria: virological ad seroepidemiological investigations in Oyo state (1979). J. Hyg. 83:213-219.

[2] Simpson, DIH. Zika virus infection in man (1964). Trans. Roy. Soc. Trop. Med. Hyg., 58:335-338.

[3] Duffy MR, Chen TH, Hancock WT, et al. Zika Virus Outbreak on Yap Island, Federated States of Micronesia (2009). The New England Journal of Medicine. 360:2536-43, http://content.nejm.org/cgi/reprint/360/24/2536.pdf  

[4] Faye O, Faye O, Dupressoir A, Weidmann M, Ndiaye M, Alpha Sall A. One-step RT-PCR for detection of Zika virus. J Clin Virol. 2008 Sep;43(1):96-101

[5] Lanciotti RS, Kosoy OL, Laven JJ, et al. Genetic and serologic properties of Zika virus associated with an epidemic, Yap State, Micronesia, 2007 (2008). Emerging Infectious Diseases. 14:1232-9, http://www.cdc.gov/EID/content/14/8/1232.htm