Chikungunya Virus and Zika Virus Expansion: An Imitation of Dengue Virus

Dengue viruses are the most important arboviral pathogens in the world, which have adapted to human transmission and replication over several hundred years and were initially recognized to cause outbreaks of clinical disease in tropical and subtropical countries by Aedes aegypti mosquitoes. Subsequent global expansion of dengue infection outbreaks has occurred, with millions of cases yearly, probably from a combination of factors including proliferation of international travel and trade, possibly global climate changes, adaptation of the vectors to new environment, and emergence of a new mosquito vector, Aedes albopictus. Chikungunya virus, also transmitted by Aedes mosquitoes, causes a very similar clinical disease but with more prominent arthralgia or arthritis and was originally described in Africa in the 1960s. After a quiescent period of several decades, it reemerged in Africa in 2004 and rapidly spread across the Indian Ocean to involve Asian countries and parts of Europe. However, the past 2 years have seen the emergence of chikungunya virus in the western hemisphere with major outbreaks in the Caribbean and the Americas. Similar to dengue virus, chikungunya virus has adapted to Ae. albopictus mosquitoes which can transmit the disease. Although dengue infection is a more deadly disease especially in young children, chikungunya infection can cause prolonged severe disability and occasionally rare fatalities from encephalitis. No specific treatment is available for either diseases, but development of an effective vaccine for dengue infection is in progress. Until 2007, Zika virus [also transmitted by Aedes species] was associated with only sporadic mild infections in Africa and Asia. In 2007, Zika virus for the first time caused an outbreak beyond Africa and Asia to the Yap Island in the Federated States of Micronesia. Since then Zika virus has spread to French Polynesia, New Caledonia, Cook Islands, and Easter Island in the southeastern Pacific Ocean [Chile] in 2014 and by 2015 to Brazil. By January 2016, it became evident that Zika virus had caused an explosive outbreak in the Americas and the Caribbean with over 30 countries affected. On February 1, 2016, the World Health Organization declared Zika outbreak a global public health emergency. Zika virus infection is most commonly asymptomatic, and 20% of patients may develop a mild viral disease, but of major concern is the reported association of microcephaly in infected pregnant women in Brazil. This chapter explores the history, epidemiology, pathogenesis, clinical features, treatment, and prevention of these rapidly emerging zoonoses.