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The Pan American Health Organization/World Health Organization (PAHO/WHO) and the Arbovirus Laboratory Network (RELDA) have agreed on new guidelines to improve lab confirmation of suspected Zika cases, even as more accurate tests are developed.
"With dengue and chikungunya circulating in the region, diagnosing Zika is a great challenge," says Maria Guadalupe Guzman, head of the Department of Virology of the Institute of Tropical Medicine Pedro Kouri of Cuba and president of the lab network. A new algorithm for lab detection of Zika virus will contribute to more accurate diagnosis and more efficient surveillance, she added.
For health services, reporting cases of Zika is difficult because up to 80 percent of infected people have no symptoms. Many cases of Zika are so mild that people don't seek medical attention. The most common symptoms are mild fever and rash, muscle or joint pain and conjunctivitis. These are similar to symptoms of dengue and chikungunya, which are also transmitted by infected Aedes mosquitoes.
Suspected Zika cases are only confirmed through blood tests. But the virus usually circulates in the blood of an infected person for five days or less. Antibodies can be detected by other tests for a longer period, but the antibodies to Zika are similar to those of dengue and yellow fever, so those tests can produce crossed results or false positives.
Jairo Mendez, PAHO's regional adviser on viral diseases, says, "The best time for laboratory testing for Zika is in the first five days of the onset of symptoms, when PCR tests can detect genetic material [RNA] from the virus." In that period, test results are more accurate than those made at a later stage where results may be presumptive.
The new guidelines consist of an algorithm based on an established regional platform for laboratory surveillance of dengue, using 22 national reference laboratories of the RELDA network. "They will serve to rule out or confirm dengue, chikungunya and Zika, and can be adjusted to the conditions of each country," says Mendez.
The diagnosis of Zika virus is important, especially for the care and monitoring of pregnant women because of the possible link between the virus and the birth of babies with microcephaly and other congenital malformations. Also there is a possible link with increased cases of neurological syndromes such as Guillain-Barre syndrome.
The aim of the new guidelines from PAHO is also epidemiological, to learn more about the behavior of the virus so as to recommend appropriate public health action to fight the disease. Currently there is no vaccine or specific treatment for Zika.
WHO is working to accelerate the availability of new and reliable diagnostic tests, with high levels of quality, safety and acceptable performance in the short term.
These actions are part of the response of PAHO/WHO since WHO declared a public health emergency of international concern due to suspicion of a causal relationship between Zika virus infection and microcephaly and other neurological disorders. Since Brazil first reported cases of Zika in 2015, the virus has spread to 31 countries and territories in the Americas.
PAHO/WHO is also working with experts from the region to develop a tool that will help physicians at the primary care level perform differential diagnosis of Zika, dengue and chikungunya. Differentiation of these diseases when laboratory tests are not available can save lives, especially of those who are infected with dengue, the deadliest of the three.
"Health personnel need to follow suspected dengue cases because dengue can kill a person if not addressed from the outset," says Jose Luis San Martin, regional adviser on dengue at PAHO. "We need clinicians trained in the presentations of dengue, chikungunya and Zika to guide the diagnosis and management of patients in the most efficient way possible."
In a meeting in Puerto Rico last week to discuss these topics, the 22 laboratories in the RELDA diagnostic network also agreed to join a WHO global network that will monitor their performance, helping to ensure quality diagnosis and continuous improvement in their technical performance.
The laboratories that make up the RELDA network decided last week to extend their work to cover other arboviruses besides dengue. As a result, the former Dengue Laboratories Network has been renamed the Arbovirus Diagnostic Laboratories Network, yielding the same acronym, RELDA, in Spanish.