ZIKA VIRUS: yet another global health concern

As at the time of writing this report, Zika virus has spread through South and Central America, and the World Health Organization has declared a Public Health Emergency of International Concern (PHEIC), warning that about 3-4 million people may be infected in 2016.

Background

a_aegypti_0Zika virus is a mosquito-borne arbovirus of the family Flaviviridae (genus Flavivirus) transmitted primarily by the Aedes mosquitoes. The virus was first discovered in rhesus monkeys in the Zika forest of Uganda in 1947 during routine monitoring of sylvatic yellow fever. The first human case was reported in 1952 in Uganda and Tanzania. Since then, outbreaks of the viral disease have been recorded in some other parts of Africa, Asia and the Pacific, the Americas, and the Caribbean. Sporadic human cases were reported in the 1960s in Asia and Africa. The first reported large outbreak of the virus occurred in 2007 on Yap Island, in Federated States of Micronesia, and another one in October 2013 in French Polynesia, a territory of France in the South Pacific. The recent outbreak, which has generated concerns internationally, began around May 2015 in Brazil, according to the Pan American Health Organization (PAHO). Following series of cases of abnormalities of the brain and eyes in the region of the outbreak, especially among newborns, evidence now suggests Zika virus infection may be associated with an increased risk of birth defects, congenital microcephaly, Guillain-Barre syndrome (a rapid-onset weakness of the muscle as a result of damage to the peripheral nervous system) and some neurological disorders. This prompted the World Health Organization to declare a Public Health Emergency of International Concern (PHEIC) on February 1 2016, warning that virus is likely to spread to other countries, particularly in the Americas, Caribbean and Africa, where the climate favours the breeding of Aedes mosquitoes.

 

Transmission and Spread

As noted above, Zika virus is transmitted to people through infected mosquitoes’ bites, which are mosquitoes of the family Aedes- the Aedes aegypti. Aedes aegypti has a characteristics black and white markings on their body and legs, and are usually very active during the daytime, with peak biting periods in early morning hours and in the evening before dusk. Aedes mosquitoes are initially found in tropical and subtropical regions, but now found on all continents except the Antarctica. It is the same mosquito that transmits dengue, chikungunya and yellow fever. If a person is infected with Zika virus, the virus may remain in the blood of the infected person for about a week, and can be passed from the infected person to another mosquito through further mosquito bites, and the cycle may just continue in the same pattern. The virus has also been found to be present in semen, and may in fact stay longer than in blood. Recently, the Centres for Disease Control and Prevention (CDC) reported that there is evidence that the Zika virus can be transmitted sexually from a man to his sex partners. There is no evidence supporting the transmission of the virus from women to their sex partners. A lot still is yet to be understood on the sexual transmission of Zika virus.

The spread of Zika virus may have taken a new shape due to climate change- rising global temperatures and changing rainfall patterns. Experts have suggested that this has possibly reshaped distribution of water-borne diseases’ vectors. In fact, a global rise of 2-3 Celsius may increase the risk of malaria in the population by about 3-5%, as mosquitoes are generally known to thrive in warmer weather conditions. It is therefore likely that recent changes in climate conditions have added to the spread of Zika virus. The 2015-16 outbreak of Zika virus started from the Americas, with sporadic cases already reported in over 13 countries in this region. Some cases have been reported in Cape Verde, an island country off the coast of western Africa.

 

Symptoms and Potential Complications

The incubation period (the time from exposure to symptoms) is still unclear, but has been thought to be about 14 days. The illness caused by Zika virus is usually mild and does not require hospitalization, lasting about 2-7 days. Common symptoms include headaches, fever, conjunctivitis (red eyes), skin rash, muscle weakness, joint pains. However, the major concern about Zika virus is that it may be harmful for pregnancies, and has been linked to birth defects, specifically microcephaly (abnormally small heads), brain damage and neurological complications. Local health authorities in Brazil observed an increase in incidence of Guillain-Barré syndrome, which overlapped with the onset and spread of Zika virus infections in the population. Just at the time of writing this report, some researchers have also published reports suggesting that “pyriproxyfen”, a mosquito insecticide used in Brazil since 2014, was probably responsible for the birth defects. Researchers have however advised that more investigations may be needed to better understand the relationship between Zika virus, microcephaly in babies, and other neurological complications.

 

Prevention and Control

As described above, Aedes mosquitoes are widely distributed especially in the tropics, so we should understand they are in Nigeria. Moreover, two African countries- Cape Verde and Gabon- have already reported cases of Zika virus in this current outbreak. According to the health minister, Zika virus was discovered in Western Nigeria in 1954. However, there is evidence that 40% of Nigerian adults and 25% of Nigerian children have antibodies to Zika virus, thus offering them protection, based on studies conducted in the 1970s.  As there are no recent studies on the virus in Nigeria, and in view of demographic and epidemiological changes since when these studies were conducted, we are advised to protect ourselves from mosquito bites. Let’s keep our surroundings clean, cut grasses, avoid indiscriminate disposal of wastes, and ensure we don’t have ponds and other potential mosquito breeding sites around our homes. Personal protection with long clothes that cover arms and legs, insect repellents, insecticides, and sleeping under mosquito nets may also be very useful. For children, the sick and elderly, who may not be able to protect themselves properly, we should kindly give them special attention and necessary assistance to protect themselves.

For people who may be travelling outside Nigeria, especially to Brazil and other South American countries, please, seek adequate travel advice from your family physician before you travel. As explained earlier, sexual transmission of Zika virus has been reported in few cases, although the risk of is thought to be very low. For people who are pregnant or trying to get pregnant, and just returning from countries with ongoing Zika virus outbreak, please, see your family physician for necessary medical advice.

 

Diagnosis and Treatment

For now, in Nigeria, Zika virus infection may be suspected based on symptoms and recent travel history since there is no active outbreak. Laboratory investigations confirming presence of Zika virus RNA in the blood or other body fluids, such as urine or saliva, is usually confirmatory. There is currently no antiviral medication for Zika virus. Treatment is usually supportive, mainly symptomatic treatment, ensuring rest, reducing fever, rehydration, and relieving pains. Fever and pains can be treated with simple acetaminophen (Paracetamol®). Please, avoid aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs), unless Dengue fever has been ruled out, as this can worsen hemorrhagic complications of Dengue fever. There is no vaccine for Zika virus.

 

Conclusion

Zika virus is yet another public health emergency of international significance. There is really no need to panic. The Minister of Health has assured Nigerians and the WHO is supporting countries with current outbreak of Zika virus. Let’s protect ourselves, embrace necessary vector control measures, and seek for relevant travel advice. Many thanks again for reading through this.  

 

Dr. Davies Adeloye is a member of the e-Health Research Cluster. He is a medical doctor and epidemiologist

 

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