OVERVIEW OF ZIKA VIRUS INFECTION

Zika virus (abbreviated as: ZIKV) belongs to the viral genus Flavivirus. It is an icosahedral, enveloped, single-stranded RNA virus that causes Zika virus disease (Zika). The lipid envelope of Zika virus is covered with dense projections that consist of a membrane and envelope glycoproteins. Zika (Zika virus disease) is a disease caused by Zika virus that is spread to people primarily through the bite of an infected arthropod (mosquito). Zika disease virus bears clinical resemblances to other Flavivirus infections or diseases such as dengue fever and Chikungunya – which are also transmitted to man via the bite of infected arthropods (mosquitoes). The mosquito species that transmit the Zika virus to man is known as Aedes mosquito. The species of Aedes mosquito that transmit the Zika virus to man via mosquito bite include Aedes aegypti, Aedes africanus, Aedes luteocephalus, Aedes albopictus, Aedes vittatus, Aedes furcifer, Aedes hensilli, and Aedes apicoargenteus. It has also been reported that sexual transmission of Zika virus amongst humans is possible.

The name Zika was from Zika forest in Uganda where the disease was first discovered. Zika virus was first discovered in 1947 and is named after the Zika forest in Uganda. Specifically, Zika virus was first described in a febrile rhesus monkey in the Zika forest of Entebbe, Uganda. Though Zika virus was first discovered in Africa, the disease and/or virus have spread beyond the African continent to other parts of the world. Several outbreak of Zika virus disease has occurred around the world since the first human outbreak of the disease was reported in 1952. Tropical Africa, Southeast Asia, and the Pacific Islands are parts of the world where Zika has been previously reported at varying prevalence’s. The first reported outbreak of Zika disease virus (Zika) in South America (precisely Brazil) was recorded on May, 2015; and this viral disease has been declared by the World Health Organization (WHO) as a public health emergency of international concern – that is likely to spread international from region to region.

The areas of active transmission of Zika virus according to the Center for Disease prevention and Control (CDC) include Barbados, Bolivia, Brazil, Colombia, Puerto Rico, Costa Rica, Curacao, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Jamaica, Martinique, Mexico, Nicaragua, Panama, Paraguay, Saint Martin, Suriname, US Virgin Islands, Venezuela, American Samoa, Samoa, Tonga, and Cape (Figure 1). Fever, rash, joint pain, and conjunctivitis or red eyes are the most common symptoms of Zika virus disease; and the clinical symptoms of the disease usually last for several days to a week after an infected person has been bitten by an infected Aedes mosquito. Zika is a mild disease and it rarely leads to death. Prior infection is likely to protect previously infected individuals from futuristic infection, and the benign nature of the disease makes most infected people especially in endemic regions not to be aware that they have been infected.

Figure 1: All countries and territories with active Zika virus transmission. CDC.

Epidemiologically, the global prevalence of Zika virus infection (Zika) has not been widely reported due to the asymptomatic clinical course of the disease and the clinical resemblance of Zika to other Flavivirus infection such as dengue fever and Chikungunya infections which are also transmitted to man via the bits of infected arthropods (Aedes mosquitoes). In addition, the diagnosis of Zika virus infection is also associated with some ambiguities. The ambiguity or difficulty associated with the accurate diagnosis of Zika is because most cases of Zika virus infection are mild and self-limited; and this makes most cases of the disease to go unnoticed. The signs and symptoms of Zika virus (ZIKV) infection are nonspecific and mimic other viral infections such as dengue fever, malaria, rickettsial infection and yellow fever. Zika virus infection is currently diagnosed based on the detection and isolation of Zika virus RNA from serum using reverse-transcriptase polymerase chain reaction (RT-PCR) in serological investigations; and the highest sensitivity of PCR testing is during the initial week of illness (i.e. at the onset of the disease.

Zika virus infection is usually characterized by high viraemia (i.e. high amount of viral particles in the blood of infected individuals). Enzyme-linked immunosorbent assay (ELISA) can also be employed to serologically test for the virus-specific immunoglobulin M (IgM) and neutralizing antibodies against Zika virus infection in patients sample (e.g. blood). Zika virus infection has been reported in various hosts including humans, primates, and mosquitoes; and these reports are based on sporadic case reports, entomological surveys, and seroprevalence surveys of the disease carried out in Zika-endemic regions of the world including Africa, Oceania and Asia – where varying prevalence’s of Zika has been previously reported. Zika virus infection is now becoming a pandemic disease – since it has spread to several continents of the world (with the latest outbreak occurring in the Americas – Brazil).

One of the most debilitating effects of Zika virus infection in humans especially pregnant women (as experienced in the lasts outbreak of the disease in the Americas – Brazil) is the congenital malformations due to transplacental transmission of Zika virus from mother to child; and other serious clinical episodes such as microcephaly, Guillain-Barré syndrome and various ophthalmologic abnormalities have been linked to Zika virus infection – which is why the disease is now a notifiable disease and a pandemic. Guillain-Barré syndrome (GBS) can be described as a collection of clinical syndromes that manifests as an acute inflammatory polyradiculoneuropathy with resultant weakness and diminished reflexes. The classic description of GBS is that of a demyelinating neuropathy with ascending weakness.

Currently, no prophylactic treatment, drug or vaccine is available for the treatment and prevention/control of Zika virus infection; and there is currently no commercially available test for Zika virus infection. However, research is ongoing to develop and make available test kits, drugs and vaccines for the accurate diagnosis, treatment and prevention of Zika virus infection in human population. Public awareness for vector control and eradication of mosquito breeding grounds in Zika-endemic regions is critical to the prevention and control of the Zika virus infection. Tourists and travelers visiting Zika-endemic countries should avoid mosquito bites as much as possible and where protective clothing’s when outdoors. Nevertheless, the best method for preventing Zika virus infection is to avoid travel to areas with active Zika virus transmission.

References

Acheson N.H (2011). Fundamentals of Molecular Virology. Second edition. John Wiley and Sons Limited, West Sussex, United Kingdom.

Alan J. Cann (2005). Principles of Molecular Virology. 4th edition. Elsevier Academic Press,   Burlington, MA, USA.

Alberts B, Bray D, Johnson A, Lewis J, Raff M, Roberts K and Walter P (1998). Essential Cell Biology: An Introduction to the Molecular Biology of the Cell. Third edition. Garland Publishing Inc., New York.

Balows A, Hausler W, Herrmann K.L, Isenberg H.D and Shadomy H.J (1991). Manual of clinical microbiology. 5th ed. American Society of Microbiology Press, USA.

Barrett   J.T (1998).  Microbiology and Immunology Concepts.  Philadelphia,   PA: Lippincott-Raven Publishers. USA.

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