Zika Virus

Author: Nikil Naveel Chand (Umanand Prasad School of Medicine & Health Science Year 3 MBBS Student 2020)

Article Updated on Thursday 1st October 2020

Zika virus is a mosquito-borne flavivirus that was first identified in Uganda in 1947 in monkeys. It was later identified in humans in 1952 in Uganda and the United Republic of Tanzania [1].

Little is known about the life cycle of ZIKV and most of the information is extrapolated from the knowledge of the other closely related flaviviruses. Zika is transmitted between humans in the urban cycle through the bite of female Aedes spp. mosquitoes [1, 2]. The virus is acquired by the mosquito during a blood meal, and upon replication in the body of the arthropod, it reaches the salivary gland and is injected at the subsequent meal into the skin of the new host. From the skin the virus spreads to the draining lymph node, where it is amplified, resulting in viraemia and haematogenous dissemination to peripheral tissues and visceral organs [3].

Following infection, an antibody- and cell-mediated immune response is induced. Specific IgM antibodies against zika have been estimated to appear approximately 4–7 days after symptom onset, followed by the appearance of IgG antibodies after 2–3 days. IgM antibodies against flaviviruses are usually detectable for 2–3 months, but may also persist for over 1 year, while IgG antibodies usually remain detectable for months or years and probably confer lifelong protection [1, 2, 4].

In most cases, Zika virus (ZIKV) infection causes a mild, self-limited illness. The incubation period is likely 3-12 days. Owing to the mild nature of the disease, more than 80% of Zika virus infection cases likely go unnoticed [5]. The rash in Zika virus infection is usually a fine maculopapular rash that is diffusely distributed. It can involve the face, trunk, and extremities, including palms and soles. Occasionally, the rash may be pruritic [5]. The rash usually occurs within the first week of illness, with the illness itself lasting from several days to weeks [5]. Aside from rash, the most common symptoms of Zika virus infection include fever, arthralgia (involving the small joints of the hands and feet), retroocular headache, and conjunctivitis [5].

According to the Centers for Disease Control and Prevention (CDC), Fiji, Samoa, Kosrae (Federated States of Micronesia), Marshall Islands, New Caledonia, and Tonga, and are currently listed among many other countries as areas of active virus transmission [1, 2, 3]. In May 2015, Brazil reported the first outbreak of Zika virus infection in the Americas. The Brazil Ministry of Health estimated around 440,000-1,300,000 suspected cases of Zika virus infection. In December 2015, Aedes aegypti and Aedes albopictus were recognized as vectors for transmission of Zika virus [1, 2]. Since then, the infection has spread rapidly to several other countries, becoming a pandemic. The association of Zika virus infection with “Guillain-Barré syndrome(GBS)” and congenital birth defects (particularly microcephaly) amid the ongoing outbreak of Zika virus infection in Brazil is still under investigation [1, 2]. In March 2016, the WHO reported that Zika virus was actively circulating in 38 countries and territories, 12 of which have reported an increase in GBS cases or laboratory evidence of Zika virus among patients with GBS ” [1,2,3].

Moreover, the diagnosis of Zika virus (ZIKV) infection is typically based on serologic testing, although the CDC now recommends urine testing. The CDC has issued interim guidance on Zika virus antibody testing and result interpretation [1].

Nonetheless, the serological diagnosis must be implemented for the study of severe cases or complications associated with ZIKV infection including:

● Neurological syndromes

● Congenital syndromes

● Fatal cases

In these cases, the clinical and epidemiological criteria are essential for the interpretation of the results. Serological diagnosis of ZIKV in Guillain-Barré and other neurological complications. Generally, suspicion of a neurological syndrome occurs outside the viremia period; accordingly, IgM antibody detection by ELISA in serum sample (or cerebrospinal fluid collected -LCR- under medical supervision) is recommended. Serological diagnosis of ZIKV in cases of microcephaly and other congenital syndromes. Given the low possibility of previous flavivirus infection in a newborn, detection of IgM antibodies ZIKV serum (or CSF) demonstrates intrauterine infection of the fetus (low probability of cross-reactivity), and given the immaturity of the immune system, a negative result does not rule out intrauterine infection.

For this reason and to find an epidemiological link, it is recommended to carry out parallel detection of IgM antibodies in maternal serum to determine recent infection [2, 3, 4]. Urine testing can also be done where the urine is tested via real-time reverse transcription-polymerase chain reaction (rRT-PCR) using samples collected less than 2 weeks following symptom onset. Urine should be tested in conjunction with serum if specimens were obtained less than one week following symptom onset. A positive result on either test confirms the Zika virus infection [3].

Supportive care with rest and adequate fluid hydration is advised. Symptoms such as fever and pain can be controlled with acetaminophen [1,5]. Use of nonsteroidal anti-inflammatory drugs (NSAIDs) in patients with unconfirmed Zika virus infection should be avoided since the use of such drugs in dengue fever is associated with hemorrhagic risk [3, 4]. The WHO recommends optimal supportive care in patients with “Guillain-Barré syndrome,” including frequent neurologic examinations, testing of vital signs, and respiratory function monitoring to decrease the likelihood of complications (eg, blood clots, respiratory failure). Patients whose symptoms are escalating rapidly or who are unable to walk should receive intravenous immunoglobulin therapy or therapeutic plasma exchange[3, 5].

Furthermore, spread and infection can be minimized by reducing mosquitoes through source reduction (removal and modification of breeding sites) and reducing contact between mosquitoes and people [5].. This can be done by using insect repellent; wearing clothes (preferably light-coloured) that cover as much of the body as possible; using physical barriers such as screens, closed doors and windows; and sleeping under mosquito nets [5]. It is also important to empty, clean, or covers containers that can hold water such as buckets, flowerpots, or tires, so that places, where mosquitoes can breed, are removed [5]. Special attention and help should be given to those who may not be able to protect themselves adequately, such as young children, the sick, or the elderly [5]. During outbreaks, health authorities may advise that spraying of insecticides be carried out. Insecticides recommended by the WHO Pesticide Evaluation Scheme may also be used as larvicides to treat relatively large water containers [5]. Travelers should take the basic precautions described above to protect themselves from mosquito bites [5].

Reference

1. About Zika Virus Disease. Retrieved from https://www.cdc.gov/zika/about/index.html. 2019.

2. Congenital Zika Syndrome & Other Birth Defects. Retrieved from https://www.cdc.gov/pregnancy/zika/testing-follow-up/zika-syndrome-birth-defects.html. 2020

3. Zika virus disease. Retrieved from https://www.who.int/westernpacific/health-topics/zika. n.d

4. Rogers, K. Zika virus. Retrieved from https://www.britannica.com/science/Zika-virus. 2020

5. Future home of something quite cool. Retrieved from https://www.health.gov.fj/?page_id=5188. n.d