Last Friday I stated Zika was in theory capable of sexual spread, and on Tues Feb 2nd, the Texas Dept State Health Services confirmed a sexually transmitted case.

Prior to the Texas announcement only one sexually transmitted case had been confirmed – Foy et al in 2011 published a case in the wife of a Zika researcher returning to Colorado in 2008. Subsequently, Musso et al in 2013 found Zika in the semen of an infected Tahitian male.

Notwithstanding the above, CDC confirm transmission is primarily via mosquitoes (Aedes – they also transmit dengue, but not malaria), and rarely, to the foetus from infected mothers.

Zika is a mild disease, predominantly with no symptoms, but with 4,800 cases of microcephaly in Brazilian babies in the last 18 months, this aspect, and the rapidity of spread of the disease (up to 1.4 million cases in Brazil in 2015) caused WHO on Monday to classify ZIKA as a Public Health Emergency of International Concern (PHEIC).

By classifying Zika as a PHEIC, WHO mobilizes internationally the resources for research and action into the disease, its sequelae, and its prevention.

WHO state there should not be travel or trade restrictions with any Zika-active country and CDC state prevention is via classic anti-mosquito measures and have issued cautionary travel advice for pregnant females

The US has the relevant Zika Aedes species in the lower states and as yet mosquito-transmission has not been documented but, with returning travelers, there is the possibility of local Zika transmission

But if Zika was first discovered in Uganda monkeys in 1947 (first human case in 1952), then appeared in the Pacific in 2007 with the first major epidemic being in French Polynesia in 2013, how did it suddenly explode in Brazil? It was not the Brazil World Cup as originally thought. Musso examined the “fingerprint” of Zika isolates in infected countries and determined that during 2013-14:

• The origin of introduction to French Polynesia is unknown
• New Caledonia was infected from infected travelers returning from French Polynesia
• French Polynesians brought the virus to Easter Island when attending the island’s Tapati Festival in early 2014
• Other nearby Pacific countries were infected because inter-travel is common
• In Aug 2014, teams from several of the above Pacific countries attended the World Canoe Championships in Rio de Janeiro. Musso suggests this introduced Zika to Brazil.

Now, in just 18 months, 28 countries have active Zika transmission.

Fortunately for New Zealand (where I live) the Ministry of Health state the subspecies of Aedes has not been found. But returning travelers with symptoms might need heed the Texas news. And spread via an accidental needlestick to an attending healthcare worker, although as yet undocumented, must also be a concern.