VIRUSES WITH HUMANS AND MOSQUITOES AS THE ONLY HOST ANIMALS

Unlike other medically important viruses transmitted by mosquitoes, humans and two Florida mosquito species are the only host animals for dengue, chikungunya and Zika viruses. Besides being transmitted by the same two mosquitoes, these viruses have very similar symptoms, lack vaccines or medications to prevent infection and require the same mosquito control measures to reduce the potential of virus transmission. The mosquitoes that transmit these viruses bite primarily during daylight hours.

DENGUE VIRUS (DENV)

Dengue is a human disease caused by any of four closely related viruses (dengue-1, -2, -3, -4). Dengue historically plagued Florida until 1934, which was the last epidemic year within the state until 2009. Since 1934, imported cases have been documented yearly in Florida. These are cases where Florida residents were infected by mosquito bites while visiting other countries with active virus transmission, but they did not become ill until returning to Florida. The Florida Keys experienced an outbreak of dengue in 2009 and 2010, followed by a small focal outbreak in Martin County in 2013. Only one locally acquired dengue case transmitted by Florida mosquitoes was reported during 2015, while 86 Florida residents received dengue infections while traveling out of country. As of June 2016 one locally acquired dengue case was reported in Florida, a tourist infected with dengue during a visit to Key West.

 

CHIKUNGUNYA VIRUS (CHIKV)

Chikungunya virus, an African virus, was first reported in the Americas in late 2013. Chikungunya is an infectious disease with symptoms that typically include fever and severe joint pain.  Like dengue, it is transmitted to humans by mosquitoes and the symptoms of exposure are very similar as well .  In 2014, Florida reported 11 locally transmitted cases, 4 of which occurred in St. Lucie County. No locally transmitted cases were seen in Florida during 2015, though 75 cases among travelers were reported. 

 

ZIKA VIRUS (ZIKAV)

Zika virus is another flavirus that originated from Africa.  Although the same mosquitoes can transmit dengue and chikungunya are known to transmit Zika, there are differences in the symptoms of the virus.  Although one in four individuals infected with Zika will experience symptoms, the negative effects are much greater than those of dengue and chikungunya.  Zika has been linked to microcephaly and other birth defects in babies and neurological impacts such as Guillain-BarrĂ© syndrome, but it can also be transmitted through sexual contact.

Zika was the cause of an outbreak of disease in the Yap Islands of Micronesia in 2007, followed by an extensive epidemic throughout the South Pacific islands. Cases were first noted in Brazil during May 2015, and by January of 2016 an estimated 1.5 million Brazilian cases had occurred. At the same time at least 22 countries in the Americas had reported Zika cases in their residents, but Zika transmission by mosquitoes had not been detected within the USA.  By the end of 2016, more than 1,100 Florida residents had aquired Zika infections while traveling outside mainland USA, 292 of the cases were pregnant females.  At the same time, 285 additional Zika cases were not imported but belived to be the result of exposure to infected mosquitoes in Miami.  This constituted the first US example of a local transmission cycle arising from frequent imported infections.