The official statistics may underestimate the size of the epidemic caused by the Zika virus because some of the Zika cases may be misreported as dengue, say Brazilian researchers. The methodologies that are currently available to the public health system and the private labs and hospitals can also produce false positives for dengue in the patients with Zika because these two viruses are so similar, said the lead researcher Mauricio Lacerda Nogueira from Sao Jose do Rio Preto Medical School (FAMERP) in Sao Paulo, Brazil. The team performed some molecular tests on the blood samples from 800 people that are treated as suspected dengue patients at the emergency facility of Hospital de Base, Sao Jose do Rio Preto’s reference hospital, between January and August 2016. The initial diagnosis, which is based on clinical symptoms and serological tests, was confirmed in only 400 samples and more than 100 of the cases analysed were positive for Zika virus. The virus that causes chikungunya fever was identified in only one of the samples. ‘These results suggest the classic division usually made between symptoms — associating conjunctivitis with Zika and joint pain with chikungunya, for example — is only for classroom use. In practice, the symptoms can’t be separated like that,’ Nogueira said.
‘It’s practically impossible to distinguish between these three arboviruses with the serological tests currently used on a routine basis by laboratories and emergency services,’ Nogueira said. New serological methods that are capable of distinguishing accurately between the Zika and dengue antibodies have been developed, but, so far they are used only in the academic research. The World Health Organisation (WHO) recommends that the all cases with an uncertain diagnosis should be treated as dengue because the risk of death from dengue is higher than from chikungunya and Zika. The false-positive results for dengue do not jeopardise the treatment of the patients, but they generate unnecessary costs for the health service, according to Nogueira.‘Rest and oral rehydration at home is sufficient for people with Zika, except pregnant women,’ he said. ‘A dengue patient, must return to the health service for intravenous rehydration and undergo more complex tests. In particular, platelet levels have to be monitored owing to the risk of hemorrhage,’ Nogueira said.