Zika virus: Transmission, Pathogenesis, Symptoms, Lab Diagnosis

Zika virus is an emerging mosquito-borne virus that was first isolated in Zika forest of Uganda in 1947. Since then, it has remained mainly in Africa, with small and sporadic outbreaks in Asia. Recent cases of Zika virus (ZIKV) infection in Brazil & American countries and its association with microcephaly have drawn the world’s attention.

ZIKV is a member of Flavivirus and Aedes mosquitoes act as a vector. So far the reservoir of ZIKV is unknown.

Zika Virus signs and symptoms
Zika virus signs and symptoms


ZIKV is transmitted to people through the bite of an infected mosquito from the Aedes genus, mainly Aedes aegypti in tropical regions. Which usually bite during the morning and late afternoon/evening hours. This is the same mosquito that transmits dengue, chikungunya and yellow fever.

One case of possible person-to-person sexual transmission of ZIKV has been described, but not confirmed.

Zika can be transmitted through blood, but this is an infrequent mechanism. The usual recommendations for safe transfusions should be followed.

Earlier, ZIKV was mainly confined in Africa with some sporadic outbreaks  in Asia. In May 2015, the public health authorities of Brazil confirmed the transmission of ZIKV in the northeast of the country. Since October 2015, it has spread to 21 countries and territories* of the Americas. (pragermetis.com)

Countries and territories with confirmed cases of Zika virus
Countries and territories with confirmed cases of Zika virus

Signs and Symptoms

The incubation period (the time from exposure to symptoms) of ZIKV disease is not clear, but is likely to be a few days.

Only one in four people infected with Zika develops symptoms, and in those with symptoms the illness is usually mild.

The symptoms are similar to other arbovirus infections such as dengue, and include fever, skin rashes, conjunctivitis (red eyes), muscle and joint pain, malaise, and headache. These symptoms are usually mild and last for 2-7 days.

Zika virus and pregnancy

Research is being done to determine what effects Zika can have on fetuses. Ministry of Health of Brazil established a relationship between an increase in cases of microcephaly in newborns and Zika virus infections. According to a preliminary analysis of this research, the greatest risk of microcephaly and malformations appears to be associated with infection during the first trimester of pregnancy. Health authorities are now conducting research to clarify the cause, risk factors, and consequences of microcephaly.

Diagnosis of Zika virus

In most people, diagnosis is based on clinical symptoms and epidemiological circumstances (such as Zika outbreak in the patient’s area or trips to areas where the virus is circulating).

Laboratory diagnosis: 

  • PCR (polymerase chain reaction): Zika virus is diagnosed through PCR tests.  PCR test gives positive results 3-5 days after the onset of symptoms.
  • Isolation of virus: Virus can be isolated from blood samples.
  • Serology: Serological tests detect the presence of antibodies after a week of infection (time taken for seroconversion). Diagnosis by serology can be difficult as the virus can cross-react with other flaviviruses such as dengue, West Nile and yellow fever.

Pan American Health Organization said, “Once it has been demonstrated that the virus is present in a given area or territory, confirmation of all cases is not necessary, and laboratory testing will be adjusted to routine virological surveillance of the disease”.

Is there a treatment for Zika?

There is no vaccine or specific treatment for Zika virus infection. Therefore, treatment for everyone, including pregnant women, is directed at alleviating symptoms.

References and further Resources about Zika virus infection is available at:  

  1. Website of Pan American Health Organization
  2. Website of Centers for Disease Control and Prevention

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

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