Читать книгу Principles of Virology, Volume 2 - Jane Flint, S. Jane Flint - Страница 32

As the Ebola outbreak was resolving in Africa in 2015, a new viral epidemic was beginning in South America. The first confirmed case of Zika virus infection in the Americas was reported in northeast Brazil in May 2015, although phylogenetic studies indicated that the virus had been introduced as early as 2013.

Zika virus is transmitted by mosquitos in temperate climates and causes a relatively mild disease in most cases: many adults seroconvert without ever knowing they were infected. However, during the 2015 outbreak it was rapidly appreciated that Zika virus infection of pregnant women can be associated with a terrifying new symptom in their newborns: small, misshapen heads (microcephaly) and severe developmental defects. As the virus spread throughout Brazil and beyond (Fig. 1.8), people in Mexico and North America quickly realized that the geographic range for the mosquito vector, Aedesaegypti, extended well into these areas. The rest of the Americas awaited the summer months braced for disaster, as mosquitos were predicted to carry Zika virus inexorably north. The outbreak coincided with the Summer Olympics in Rio de Janeiro, and prompted many enthusiastic supporters and athletes to stay home. For reasons still unclear, these fears did not materialize. By 2017, most of Latin America and the Caribbean had a massive decline in Zika virus infections. It has been suggested that the sharp reduction in cases is due, at least in part, to a phenomenon known as herd immunity (Chapter 7). Virus transmission between humans and mosquitos is greatly reduced in a population when enough people become immune to a virus, through vaccination or, as in the case of the Zika virus, natural immunity following infection.

Figure 1.8 Zika spread in Brazil. (A) In three short years, from 2014 to 2016, Zika virus moved progressively north and westward, spreading from the coastal region of Brazil to other countries in South America. (B) Decline of Zika virus cases since 2016. Adapted from Lowe R et al. 2018. Int J Environ Res Public Health 15:E96, under license CC BY 4.0.