Zika in Brazil: Olympic Update
In April, the WHO concluded there is a causal relationship between prenatal Zika virus infection and microcephaly in newborns. It noted that no single piece of evidence provides ultimate proof of the link, rather, the conclusion is supported by evaluation of the growing body of academic literature.
The level of risk associated with prenatal infection has not been precisely quantified. A retrospective analysis of the 2013–2015 Zika virus outbreak in French Polynesia estimated the risk of microcephaly was approximately 1% for women infected in the first trimester of pregnancy.
The data on the current outbreak is too muddy to calculate an exact figure, but the numbers show a clear trend. In 2014, 147 microcephaly cases (total) were recorded in Brazil. As of July, 8,703 cases had been reported during the 2015–2016 Zika outbreak. Of these, 1,749 have been confirmed as relating to the virus.
With the eyes of the world focused on the Rio Olympics, it seems like a good time to take stock of how the Zika virus has progressed in Brazil, and assess the wider implications of the outbreak. Nine key points are listed below:
1. The majority of PAHO countries have reported Zika virus cases.
Approximately 42 countries and territories in the Americas have confirmed local, vector-based transmission of the Zika virus since 2015.
2. Brazil has bore the brunt.
Of the 89,502 confirmed Zika cases across the Americas , over 74% were recorded in Brazil.
3. And the suspected number of infections dwarfs the confirmed cases.
The suspected number of total Zika infections in Brazil is around 2.5x higher than the confirmed figures, which only include samples that have been laboratory tested for the virus. This puts the total number of suspected infections at approximately 168,000.
4. The incidence of the disease has actually fallen dramatically.
Since February, the number of new cases per week has fallen to almost zero.
5. But, this decline is likely due to seasonality.
The January/February peak coincided with the WHO declaring the Zika outbreak to be a global health emergency. But Zika is not now under control, Brazil is merely benefiting from the weather. The primary vector of the Zika virus is the Aedes aegypti mosquito and Brazil is now in winter. The cooler and drier weather reduces mosquito populations, lowering the risk of vector-borne transmission. It is also important to note that the global incidence of Zika infection is still rising; the virus is not going away anytime soon.
6. The virus may have moved beyond its original host species.
Recent evidence suggests that, in addition to the Aedes aegypti, Zika virus can also be transmitted via Culex quinquefasciatus mosquitoes. Culex mosquitoes are more widespread than the Aedes genus. They breed in dirty water and bite at night (unlike their Aedes friends). If this link is confirmed, it would require a whole new set of strategies to combat the virus.
7. Which further reinforces the importance of vector control.
Part of the reason Brazil has suffered more than other countries from Zika is because its vector control (mosquito control) sucks. It lacks the frameworks and surveillance programmes that many tourism-reliant countries in Latin America use (and rely upon) to support economic growth.
8. Regional inequality hasn’t helped the issue.
Zika cases have been disproportionately concentrated in the north-east region of Brazil . There are environmental reasons for this, but at the same time, the nine states of the north-east happen to be some of the poorest in the country. Maranhão state recorded the lowest GDP per capita (USD3,197) of any Brazilian state in 2015. It is possible that local governments lack the cash to fund sufficient vector control programmes.
9. A vaccine is a distant hope, but diagnostics are getting better.
There is no cure against Zika virus, and despite the launch of a number of Phase I vaccine trials, a product is not expected until 2018 (in the best case scenario). Instead, immediate efforts have turned to diagnostics. The typical diagnostic test for Zika is laboratory-based reverse transcription PCR. However, this can often be time consuming (and expensive).
In response more rapid approaches have gained traction. In February 2016, the Brazilian health surveillance agency approved a 20-minute Zika test. This was the fourth Zika diagnosis product approved by Brazil’s health agency.
This post is an adaptation of a note I wrote for clients of BMI Research.
