New Network Analysis in Zika Outbreak Discussion

With the 2016 Rio Olympics only a few months away there has been much discussion about the outbreak of the Zika virus in Brazil and it’s impact on the spread across the country. This has lead to a discussion and a petition of over 150 professors at top schools such as Harvard, Yale, Oxford, University of Tokyo, Columbia, New York University, University of Pennsylvania, Princeton and others calling for a postpone in the games until the outbreak is controlled. In their petition to postpone the Rio Olympics they list such issues as:

“The evidence shows: (i) that Brazil’s Zika virus strain has more serious medical consequences than previously known, (ii) that Rio de Janeiro is one of the most affected parts of Brazil, and (iii) that Rio’s mosquito-killing efforts are not meeting expectations, but rather mosquito-borne disease is up this year.”

Zika virus disease is a disease caused by the Zika virus, which is spread to people primarily through the bite of an infected Aedes species mosquito. The most common symptoms of the disease are fever, rash, joint pain, and conjunctivitis (red eyes). The illness is usually mild with symptoms lasting for several days to a week after being bitten by an infected mosquito. People usually don’t get sick enough to go to the hospital, and they very rarely die of Zika and for this reason, many people might not realize they have been infected. However, Zika virus infection during pregnancy can cause a serious birth defects such as microcephaly, where a baby is born with a head much smaller than expected, as well as other severe fetal brain defects.

The first confirmed Zika virus infection in Brazil was found in May 2015 and on February 1, 2016, the World Health Organization declared Zika virus a Public Health Emergency of International Concern as local transmission has been reported in many other countries and territories.

Despite all of this the World Health Organization decided to reject the call to move or pospone the Rio Olympic Games over the Zika outbreak. In their response they list “this would “not significantly alter” the spread of the virus”. This comes out the same day as a new network analysis of the situation was released in Japan.

A new study conducted by a team of researchers from the University of Tokyo, Hokkaido University, and the Japan Science and Technology Agency in Japan have developed a tool for predicting the risk of Zika virus importation and local transmission for 189 countries.

Network Photo 1

Global distribution of the risk of local transmission with Zika virus.
The risk is given as the percentage of observing local transmission by the end of 2016, clored by intensity (0-15, 15-30, 30-45 and 45-60%, respectively). The origin country Brazil and countries that have already experienced case importation prior to importation event in Brazil are colored by grey.

The team predicted the virus’ potential of importation and local transmission by the end of 2016. In it they used a survival analysis model, information about airline transportation networks, and transmission data for dengue and chikungunya viruses, which are also transmitted by the same mosquito species. The model they use is similar to the SIR epidemic model described to us in class. The model goes through different accounts of country susceptibility, it’s level of infectiousness, and also emits (removes) the nodes that have already experienced case importation. This is done at a much more in depth and technical level than that of the course, however what we have learned is core to the research on the outbreak.

Network Photo 2

(A–B) List of top 30 countries with the estimated highest risks. (A) shows the risk of importation, while (B) shows the risk of local transmission. The risks shown on horizontal axes represent our estimates by the end of 2016 (week 92). Bars filled with grey represent countries that have already experienced importation of ZIKV infected case(s) by 31 January 2016 (week 46).

As this information is so recent it is unclear of the effect that this new study will have on the Rio Olympics situation. However it is very interesting seeing a epidemic network analysis being done on a global scale that is relevant in all countries. Especially a day after we went over Epidemics in class.


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