Saturday 19 November 2016

Determining the origin of the August 2016 Singapore Zika Virus outbreak.

Zika Virus was first recoded in 1947 in Rhesus Monkeys in Uganda, with a series of sporadic Human infections recorded in Africa and Equatorial Asia in the later part of the twentieth century. In 2007 a larger outbreak was recorded on the island of Yap in Micronesia, which was followed by a second outbreak in French Polynesia in 2014-15. This Polynesian outbreak was particularly worying as it was linked to a variety of congenital cerebral defects, including microcephaly (extreme underdevelopment of the brain in infants, leading to severe learning disabilities). This was followed by a larger outbreak in 2016 which originated in Brazil and spread to a number of other American nations, an outbreak which was again linked to a cerebral defects, including microcephaly.

In August 2016 a cluster of Zika cases was detected in Singapore, causing fears that the disease may have spread from Brazil, and might present a danger to pregnant women in the country. In a paper published in the journal Eurosurveillance on 22 September 2016, a team of scientists led by Sebastian Maurer-Stroh of the Bioinformatics Institute of the Agency for Science, Technology and Research in Singapore, the Department of Biological Sciences at National University of Singapore, the School of Biological Sciences at the Nanyang Technological University and the National Public Health Laboratory of the Singapore Ministry of Health, describe the results of a series of an investigation into the Singapore Zika Virus outbreak.

The Zika Virus. Getty Images.

The Zika Virus has been known to be split into two distinct lineages, the African and Asian lineages, with the Micronesian, Polynesian and Brazillian epidemics all being derived from the Asian strain. Importantly the Polynesian and Brazilian Zika Viruses are more closely related to one-another than to any other recorded strain of the Virus, implying that the cerebral defects that are associated with the Virus are probably the result of a mutation present only in these strains.

Maurer-Stroh et al. tested 153 patients showing Zika-like symptoms (rash, polyarthralgia and low grade fever, and in a number of cases had mild conjunctivitis) in Singapore on 27-28 August 2016. Of these 53 tested positive for the Virus. RNA sequencing of the Viruses (Zika is an RNA Virus which lacks DNA) revealed that the Singapore Virus belonged to the Asian strain, and though it was outside the Polynesia/Brazil cluster, it was more closely related to this cluster than any other tested strain.

Maximum likelihood phylogenetic tree of representatives from the African lineage coloured red and Asian lineage coloured blue or cyan. The tight cluster with strains from French Polynesia and the Americas is in blue and strains from south-east Asia are in cyan. Maurer-Stroh et al. (2016).

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