Zika, a mosquito-borne disease that can also be transmitted through sexual contact, recently emerged as a public health threat following an increase in birth defects seen among infants of infected women.
Zika is a Flavivirus, a family of viruses including yellow fever, dengue fever and West Nile virus.1 The virus was first isolated in Uganda in 1947 in a Rhesus monkey used to study the dissemination of yellow fever. Since then, Zika in humans has been limited to isolated outbreaks in African and Asian countries.
In most cases, people infected with Zika develop a mild illness characterized by red spots spread throughout the body (maculopapular rash), low fever, arthralgia, arthritis, myalgia, and headache. However, more severe manifestations can be observed, including characteristic signs of Guillain-Barre syndrome, a serious autoimmune disease that affects the functioning of the peripheral nervous system and can cause muscle weakness and (usually reversible) paralysis. There has also been an alarming increase in the number of cases of microcephaly (a condition in which a baby’s head is much smaller than expected often because its brain has not developed properly) and other birth defects among infants born to women infected with Zika in the beginning of gestation.
In 2015, a serious outbreak occurred in Brazil and quickly spread throughout Latin America. In February 2016, the World Health Organization (WHO) declared Zika a Public Health Emergency of International Concern.2
Because there is currently neither a vaccine to prevent infection nor any approved medicine to treat the disease,3 reducing transmission is an urgent priority for containing the spread of Zika. Rapid, accurate screening of the Zika virus, therefore, is critical to identifying infected individuals and implementing infection control measures. This was reflected in the WHO’s declaration, which also called for the prioritization of the development of new diagnostics. However, a number of significant challenges stand in the way. The symptoms associated with Zika, dengue and chikungunya are often similar, increasing the possibility of misdiagnosis based solely on clinical judgments. The three viruses are transmitted using the same vector, Aedes aegipty, resulting in infection at the same epidemiological moment. In addition, antibody tests for the Zika virus often cross-react with dengue viruses due to antigen sequence similarities. Due to lack of a point-of-care test that performs well on Zika, test samples must be sent to central laboratories for confirmation. Unfortunately, management and logistical challenges and lack of resources for sample transportation often delay availability of results. Potentially infected patients are lost to follow-up or receive the results too late to guide clinical decisions.
One important question that emerges when fighting this epidemic is: should the required laboratory test for diagnosis be molecular or serology based? This is a complex question because of the behavior and characteristics of arboviruses when they infect humans. On average, the viruses can be detected in plasma or blood up to 5 days after patients’ symptoms first appear. For Zika and chikungunya, the virus is detectable in urine up to 15 days. After two weeks, molecular tests lose sensibility and are not useful for diagnosis. IgM/IgG antibody tests become useful when patients present late at clinics and a differential diagnosis is still needed.
Ultimately, healthcare workers will need an accurate point-of-care test for Zika, chikungunya and dengue that can be used in the field and that provides results in an actionable timeframe. As we have seen in HIV, malaria and other infectious diseases that disproportionately affect developing countries, point-of-care testing is often the only viable approach for screening at-risk people who cannot easily access clinics and other traditional healthcare facilities. With the availability of rapid results, healthcare workers can detect infection while still with the patient, facilitating either immediate linkage to treatment, as in chikungunya with the implementation of anti-rheumatic drugs or, as in the case of Zika, in a pregnant woman, to use ultrasound to monitor fetal development closely, and immediate implementation of infection control measures.
Industry, government and the global health sector should make the development and availability of a point-of-care Zika, chikungunya and dengue assay their shared objective and should work together to achieve this goal.
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