The United States season for mosquitos is now upon us. With mosquitos comes new worries such as itching, inflammation, infections, Zika, Dengue, and other worries.
 The Zika virus outbreaks are spread across many countries, including Africa and Asia-Pacific.  The countries expected to be at the greatest risk are India, China, the Philippines, Indonesia, Nigeria, Vietnam, Pakistan and Bangladesh.  This is due to a combination of high travel volumes from Zika affected areas in the Americas, local presence of mosquitos capable of transmitting Zika virus, and suitable climatic conditions in the large populations (and/or limited health resources).  The new modeling study was published in The Lancet Infectious Diseases.  According to the authors identifying where and when populations would be most susceptible to local transmission of Zika virus, could help inform the public health decisions about the use of finite resources.

There are around 1.6 billion people that live in areas of Africa and Asia-Pacific where the local mosquito species and climatic conditions mean that the Zika virus transmission is theoretically possible.  There are many unknowns concerning the virus and how it actually spreads.  Of course, mosquitos are most capable of transmitting the virus.  A lot will depend upon the country’s ability to diagnose and respond to a possible outbreak, according to the study author Dr. Kamran Khan from St Michael’s Hospital in Toronto, Canada.  During the warmer temperatures in the northern hemisphere, the risk of new outbreaks appearing outside of the Americas is increased and also when the mosquitos are more active.

It is particularly concerning given the vast numbers of people who could be exposed to Zika virus in Africa and the Asia-Pacific region, where health and human resources to prevent, detect and respond to epidemics are limited.

In a study the researchers gathered data on airline ticket sales from all 689 cities with one or more airports in the region, traveling to Africa or Asia-Pacific over a whole year, from Dec of 2014 to Nov of 2015.  Then they modeled 3 different scenarios of seasonal suitability for mosquito-borne transmission of Zika virus.  The team also mapped the monthly volume of travelers arriving into Africa and Asia-Pacific in order to identify countries at the greatest risk of Zika importation across seasons.  Those countries showing large volumes of travelers arriving from Zika virus-affected areas of the Americas and large populations at risk include India, China, Indonesia, the Philippines and Thailand.

It is suggested that countries with the largest at risk populations are India, the Philippines, Indonesia, Nigeria, Vietnam, Pakistan and Bangladesh because of their limited per capita health resources.  Sexual transmission is now well documented and travelers returning from affected areas would benefit from health education to prevent sexual transmission.  The health consequences of imported Zika virus will depend on local ability to diagnose and respond to a possible outbreak, but will also depend on possible underlying levels of immunity to Zika virus.  Sporadic cases of Zika virus have been reported in both Africa and Asia-Pacific.  It is also not known if the current Asian strain of the virus will affect individuals differently if they have previously been infected with the African strain.

Dr. Abraham Goorhuis and Professor Martin P. Grobusch, Center of Tropical Medicine and Travel Medicine, University of Amsterdam, Amsterdam, Netherlands said “An important prerequisite for the occurrence of large-scale epidemics is the presence of an immunologically naïve human population.  This is a big unknown in the high-risk countries identified, because urgently needed reliable seroprevalence studies are in short supply.”

This detailed study was funded by the Canadian Institutes of Health Research.

–Dr Fredda Branyon

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