Will Brazil's Next Epidemic Come from Another Mosquito-Borne Virus?

As researchers continue to make strides in learning more about the mosquito-borne viruses that have been plaguing Brazil, a new study has found that the next disease epidemic to hit the country could be Chikungunya.

According to the results of a recently published PLOS Neglected Tropical Diseases article, Aedes mosquitoes in Aracuja city in Sergipe State, Brazil, were found to be “naturally infected” with the East-Central-South-African (ECSA) Chikungunya virus genotype. Although there have been thousands of Chikungunya cases identified in Brazil, until now, they have all been identified as travel-related.

The researchers collected 248 mosquitoes from inside and outside of homes in the urban areas of the city. Four mosquito strains were collected, the most common of which were Culex quinquefasciatus (78.2%) and Aedes aegypti (20.2%) mosquitoes. The mosquitoes were tested for Zika, Dengue, and Chikungunya using QuantiTect Probe reverse transcription-polymerase chain reaction (qRT-PCR) and Mastercycler Realplex 2 thermocycler.

Mosquitoes from Aracuja were tested for these viruses because the city is known to be endemic for Dengue, and because Zika and Chikungunya cases had been confirmed in the city in 2016. In addition, studies have shown that co-infection with Zika and Chikungunya may lead to complications.

Of the collected mosquito pools, all pools tested negative for Zika and Dengue (genotypes 1-4). One female pool of Ae. aegypti mosquitoes (38 mosquitoes) tested positive for Chikungunya virus, although all male pools (12 mosquitoes) tested negative. When the female mosquitoes in the Ae. aegypti pool were individually tested, only one mosquito was positive for Chikungunya. According to the Centers for Disease Control and Prevention, Chikungunya “is most often spread to people by Aedes aegypti and Aedes albopictus mosquitoes.” The authors note that they did not identify any Aedes albopictus mosquitoes “in the inspected houses, although this species is endemic in Aracuja city.”

“Our findings constitute the first description of Ae. aegypti-[Chikungunya] genotype ECSA interaction in Brazil. These results reinforce the role of this species as an important vector of [Chikungunya] in urban areas of northeast regions in Brazil,” stated the authors of the study.

Previous studies have shown that co-infection with Chikungunya and Zika may result in prolonged Zika virus RNA shedding, which may increase the severity of infections. “There may be a trend between persistent [Zika virus] RNA shedding and prolonged symptoms,” remarked Contagion^® Editorial Advisory Board member Marta G. Cavalcanti, MD, PhD back in February 2017, in a session at the First International Conference on Zika virus. In addition, Dr. Cavalcanti noted that higher morbidity rates were identified among those with Zika and Chikungunya co-infection

Additional research analyzing the impact of the Zika virus epidemic in Brazil was recently published in The Lancet on June 21, 2017. The authors of the Lancet study analyzed the effects of the Zika epidemic in the Brazil between November 2015 and 2016, one year after the Ministry of Health declared Zika a Public Health Emergency of International Concern.

After collecting data on cases of Zika virus infection and microcephaly between January 1, 2015 and November 12, 2016, the authors found that of the total 1,673,272 reported cases of Zika virus in the country, 41,473 (2.5%) were reported to be pregnant women. A total of 1,950 cases of microcephaly resulting from congenital Zika infection were also confirmed.

The researchers discovered that there were “two distinct waves of Zika virus infection” that impacted all regions of Brazil in 2015 and 2016, with most cases occurring in the northeast region of the country after the first wave of Zika. The second wave of Zika was reported to have impacts in all regions of Brazil, and occurred between September 2015 and September 2016. The authors concluded that “occurrence of microcephaly was much lower than that following the first wave of Zika virus infection, reaching epidemic levels in all but the south of Brazil, with estimated monthly peaks varying from 3.2 cases to 15 cases per 10,000 births.”

The Lancet authors concluded, “The distribution of infection-related microcephaly after Zika virus outbreaks has varied across time and Brazilian regions. Reasons for these apparent differences remain to be elucidated.”

Although the Zika epidemic may be over in Brazil, the news of the potential for a Chikungunya epidemic in the same region begs the question, what will the clinical signs be for those with Zika virus infections who also acquire Chikungunya?