Zika virus: A pandemic in progress

Abstract

The world is facing a number of emerging infections. The latest outbreak of Zika virus infection has only added to the suffering. The WHO declared a state of emergency in the affected countries and has issued alarms worldwide. The paucity of literature leading to lack of clear guidelines is one of the most important factors resulting in a higher number of cases. The absence of clinical vaccine and an antiviral drug may prove to be a really grave situation. The present paper throws some light on this new emerging virus that has been known to man since 1947.

Introduction

The world is facing a pandemic in progress named Zika virus (ZIKV) infection. The scientific data about this new emerging virus that is known to man since 1947 is still scarce.^{[1, 2]} The ZIKV is an arthropod-borne virus belonging to the genus Flavivirus of the family Flaviviridae, and is closely linked to other virus of the same family such as dengue, yellow fever, West Nile, and Japanese encephalitis viruses.^[3–6] ZIKV was first isolated from Zika forest in Uganda from a febrile sentinel rhesus monkey and from the mosquito vector, Aedes africanus, in the year 1947 and 1948, respectively.^{[3, 7]} These initial isolations were followed by detection of ZIKV in humans, mosquitoes, and other animals in Africa and Asia by virus isolation and serological studies.^{[3, 8–13]} On the basis of comprehensive genomic comparison showing different sub-clades, the existence of two main lineages, one African and one Asian lineage of ZIKV have been reported.^[14–18] The African lineage is divided into East and West African clusters, some authors described three different lineages (West African, East African, and Asian).^[16–19] The Asian lineage is extending, this lineage emerged in the Pacific and in South America.^{[17, 20–22]}

Epidemiology and transmission

Previous studies have demonstrated that ZIKV is endemic to Africa and Southeast Asia.^{[6, 12]} Till the year 2007, only 14 cases of ZIKV infection in humans were reported.^{[6, 18]} But in the year 2007, an epidemic of ZIKV infection in humans from the Yap, Federated States of Micronesia was reported.^[6] A survey of seroprevalence reported that ≤ 70% of the population had been infected.^[5] After that, during 2007–2013, the few cases of infection with ZIKV reported were in travelers returning from afflicted countries of Africa or Southeast Asia.^{[23, 24]}

The ZIKV is transmitted primarily by Aedes spp. mosquitoes that are infected.^{[6, 7, 12, 25, 26]} Cases have been reported from elsewhere in the world and also from the developed countries that could well be attributed to patients having traveled to the afflicted countries.^[6] The scientific data about this virus is sparse and no clear picture about the exact life cycle, transmission, pathology, clinical features, diagnosis, and management is available. However, the recent reports published have thrown some light on the possible transmission, clinical features, diagnosis, and management, but still no clear guidelines based on the studies to manage this new emerging virus in the absence of a drug or vaccine are available.^{[1, 33]}

Clinical presentation

As per an estimate, about 80% of persons infected with ZIKV are asymptomatic or mildly symptomatic.^{[6, 28, 29]} In humans, ZIKV infection is characterized by mild fever (37.8–38.5°C); arthralgia, mainly of small joints of hands and feet; headache; myalgia, retro-orbital pain; conjunctivitis; and cutaneous maculopapular rash.^{[6, 29]} There are other symptoms as described elsewhere and thus, no specific presentation of ZIKV is available.^[6] Symptoms usually last from several days to one week and is managed by supportive care.^[1] As ZIKV infection is mild, so it can be easily misdiagnosed during the acute (viremic) phase because of nonspecific influenza-like signs and symptoms. Also, in countries where other flaviviruses virus are also present, it is very difficult to diagnose the ZIKV, especially in situations where the viral load is low due to the cross-reactivity of ZIKV antibodies with other flaviviruses.^[1] Hospitalization in ZIKV illness is uncommon, and fatalities are rare since the disease is not severe.^[30] Hemorrhagic signs have not been reported in ZIKV-infected patients.^{[5, 23, 24]} However, neurological complications, including Guillain-Barré syndrome, have been observed in suspected cases.^{[6, 31–33]} Also, the ZIKV has emerged with a sudden outbreak of cases of microcephaly with a 20-fold increment in the recent births and has raised alarms.^[34–36] The situation in certain countries is so grave that the government officials have advised for postponement of pregnancies till 2018.^[37] The evidences of ZIKV being isolated from the amniotic fluid and other specimens of the babies along with a history of travel to an endemic or ZIKV-affected country by a mother, are some of the indicators correlating the cause with the new arbovirus. The reports of higher chances of infection in the third trimester are available, but as per the CDC, pregnant women can be infected with ZIKV in any trimester.^[38–40]

Diagnosis and management

Biological confirmation of ZIKV infections is based mainly on the detection of virus RNA in serum by using reverse transcription Polymerase Chain Reaction assays. Although IgM against ZIKV can be detected by ELISA, but this test is not widely available.^[1] Thus, in addition to the nonspecific clinical features of infection with ZIKV, laboratory diagnosis is challenging because of low viremia and cross-reactivity of ZIKV antibodies with other flaviviruses, which require confirmation by neutralization assays and thus, making the rapid serologic confirmation difficult.^[31] ZIKV has been reported to be isolated from various types of samples such as blood, saliva, urine, semen, amniotic fluid, umbilical cord and so on and thus, further studies aimed at finding a quicker and cheaper diagnostic technique for the ZIKV is warranted. The samples of blood and saliva are really important at the early detection of ZIKV during the stages of acute viremia.^{[6, 19]} The role of samples such as saliva is especially important in conditions where other samples are difficult to obtain.^{[6, 41]} The virus can also be traced from urine samples after one week of onset of symptoms.^[6]

The protection from the mosquito bites by avoiding travel to ZIKV-infected countries and control of mosquito vector is the mainstay of the prevention from ZIKV.^{[42, 43]} In countries where the per capita income is low and a fraction of the annual budget goes to health, the situation can become really grave.^[44–46] Lack of complete knowledge and clearer action plan could lead to a very serious situation and thus, the role of proper dissemination of healthcare information to the general public is very important and all the stakeholders such as the governments, health care providers, and NGOs such as HIFA2015 and so on should play an active and an important role.^[47–49]

Conclusions

The new emerging ZIKV infection in various countries demands actions to be taken at the grassroots level. The current situation is really discouraging as new infections are developing and spreading at a fast pace. If the ZIKV infection spreads widely then it may lead to a lot of hue and cry, especially from Asian countries. The havoc created by other flaviviruses such as dengue, Chikungunya and so on has already resulted in a lot of public health issues and thus, in such a situation, the ZIKV could only result in real chaos. The absence of sufficient literature has led to real concern as there are no clear guidelines for the control of the ZIKV infection.

The role of clinicians, public health officials, non-profit organizations, and high-quality reference laboratories is very important. Extensive research for the development of exact guidelines for control and prevention of this disease is warranted as the ZIKV is still a pandemic in progress. Also, the ease with which the exotic pathogens are transmitting from one continent to another should be studied in detail and methods to control this transmission be developed. There is a need for strong clinical vigilance and epidemiologic and laboratory surveillance systems to detect the spread of infectious diseases. Efforts should be made to increase awareness among the lay public about the virus and protective measures to be taken.