Chikungunya was introduced into the Americas in 2013, with cases in several US territories. Many imported cases have been reported from travelers returning to the US.
Chikungunya only affects humans and is spread by non-native Aedes mosquitoes.
The virus most often causes fever and joint pain in humans 3-7 days after infection, and can also cause other symptoms such as headache, muscle pain, joint swelling, or rash.
Dengue occurs in moist habitats in tropical and subtropical environments worldwide and in the southeastern US, with climate change promoting spread of the disease to the north.
Dengue primarily affects humans and is spread by non-native Aedes mosquitoes.
Dengue causes flu-like symptoms in some people and no visible signs of infection in others.
Zika virus was introduced into the Americas in 2015 and has spread to many US territories, with many imported cases in the US. Only 1 in 5 people infected will get sick.
Symptoms develop 3-14 days after infection and include fever, joint aches, rash, and red eyes. Zika infection during pregnancy can cause miscarriages, brain damage and microcephaly in the fetus. There have also been increased reports of Guillain-Barre syndrome, a paralytic condition, that may be associated with Zika infection.
Zika is spread by non-native Aedes mosquitoes, sexual transmission, and from a mother to fetus. Wildlife do not play a role in maintaining or transmitting the virus.
Eastern Equine Encephalitis (EEE)
Eastern Equine Encephalitis (EEE) is a viral mosquito-borne disease occurring in wooded wetland habitats in the Gulf Coast and Atlantic states and Great Lakes region of the US.
The disease affects humans and animals including birds, horses, and sometimes other mammals including deer.
Most humans do not develop any symptoms of EEE. Less commonly, severe EEE can cause seizures, confusion and life-threatening swelling of the brain in humans.
La Crosse Encephalitis
La Crosse Encephalitis occurs in forests in the Midwestern, mid-Atlantic, and southeastern US.
The disease affects humans and small rodents and is caused by a virus spread by the eastern treehole mosquito (Aedes triseriatus).
La Crosse Encephalitis virus causes no visible signs of infection in most people and flu-like symptoms in some.
Serious cases, most often in children younger than 16 years old, can cause swelling of the brain, which is life threatening and requires emergency medical treatment.
West Nile Virus
West Nile Virus (WNV) occurs throughout the world and is carried by many species of mosquitoes.
The disease is transmitted to humans, birds, and other animals including horses by the bite of infected mosquito.
The majority of infected humans do not develop any symptoms from WNV, although some experience flu-like symptoms and few develop serious neurologic illness.
Birds such as raptors are very susceptible to the disease and often develop severe illness and die. WNV has decreased bird populations in many areas.
Report dead birds to a park ranger as they may indicate that WNV is circulating between birds and mosquitoes.
Western Equine Encephalitis
Western Equine Encephalitis (WEE) is found in grassy, wetland habitats and the plains regions of the western and central US.
The disease affects humans and animals including birds, horses, and sometimes other mammals such as deer.
Most humans do not develop any symptoms of WEE. Less commonly, severe WEE can cause seizures, confusion and life-threatening swelling of the brain in humans.