The ever-growing problem of Zika virus
By Archie Clements
The rise in prevalence of Zika virus in South America during the past 12 months has caught authorities on the hop.
And while research continues into the health impacts of the virus and any potential links to microcephaly, millions of people travelling into the worst-affected region for the Olympics in August adds another layer of complexity to a delicate situation.
Zika is a virulent virus from the same family as dengue fever and yellow fever. Infection in humans arises about 10 days after a bite from an infected mosquito and results in headaches, rashes, chills, vomiting and joint and muscle aches.
Zika, like dengue fever, is emerging as a global problem that rightly led to the World Health Organization (WHO) declaring Zika to be a global public health emergency.
Both Zika virus and dengue fever are transmitted by the daytime-active Aedes mosquitos, especially Aedes aegypti.
Zika had largely impacted small groups in tropical Africa after being discovered in Uganda in the 1940s but the first large-scale outbreaks occurred in French Polynesia during 2013 and 2014.
In the second half of 2015, Zika spread across South American countries, with Brazil the epicentre of infection.
In Brazil, particularly, there have been a number of main issues that have led to its dramatic rise.
The Brazilian population was naïve to the impact of Zika.
Its people had built up no immunity to the virus and the mosquito is now present in large numbers, despite a previous successful eradication of the Aedes aegypti mosquitos in the 1950s.
This, along with rapid growth in international travel in the region as a result of a booming Brazilian economy, has spurred on the Zika virus.
Another challenge is the behaviour of the Aedes aegypti mosquitos, which only bite people during daytime hours.
This is different to malaria, which is transmitted by Anopheles mosquitos that only bite during the night time.
As a result, sleeping under a mosquito net, for example, can provide protection against malaria but not Zika.
Aedes aegypti mosquitos have evolved to like being near people in peri domestic urban areas, where they breed in small accumulations of water, such as in upturned tyres and rubbish bins.