Arbovirus (arthropod-borne virus) applies to any virus that is transmitted to humans and/or other vertebrates by certain species of blood-feeding arthropods, chiefly insects (flies and mosquitoes) and arachnids (ticks).
Mayaro disease
Mayaro virus is an alphavirus in the Togavirus family.
Mayaro disease is a dengue-like disease transmitted by mosquitoes infected with Mayaro virus. It is common in Brazil and Bolivia and is endemic in the tropical areas of South America (Trinidad, Suriname, French Guyana, Brazil, Peru, Bolivia, and Venezuela). A 2014 case in Trinidad and a 2015 case in Haiti suggest that there is potential for spread to other areas in the Americas that have abundant population of Aedes aegypti.
Prevention of Mayaro disease involves avoiding mosquito bites. No vaccine is available.
Oropouche fever
Oropouche virus is a Simbu group bunyavirus.
The oropouche virus is transmitted to humans by Culicoides paraensis, a species of biting midges (small flying insects) present in South and Central America and the Caribbean.
Transmission of the oropouche virus occurs in 2 cycles:
Wild
Urban-epidemic
In the wild cycle, the reservoir for the oropouche virus is wildlife (eg, primates, sloths, certain arthropods). In the urban-epidemic cycle, humans are the principal reservoir, and the infection cycle is human to human via the midge vector.
The oropouche virus has been moving closer to major cities in Brazil, and some public health officials think that the virus has major epidemic potential throughout the area in which it occurs. The World Health Organization recommends that oropouche fever be included in the clinical differential diagnosis for other common febrile arboviral infections (eg, chikungunya disease, dengue, yellow fever, Zika) (1).
In humans, oropouche fever resembles dengue, causing acute fever and infection, which may lead to meningitis and meningoencephalitis.
Treatment is supportive.
Prevention of oropouche fever involves avoiding midge bites. No vaccine is available.
Tick-borne encephalitis
Tick-borne encephalitis is caused by a flavivirus that has 3 subtypes, European, Siberian, and Far Eastern.
Tick-borne encephalitis is transmitted to humans in focal areas extending from eastern France to northern Japan by the bite of infected hard–bodied ticks, Ixodes ricinus in Europe and Ixodes persulcatus in Siberia and the Far East. Ticks are both vector and virus reservoir, and small rodents are the primary amplifying host. Tick-borne encephalitis can also be acquired by ingesting unpasteurized dairy products (such as milk and cheese) from infected goats, sheep, or cows.
Cases occur from early spring to late summer when ticks are most active. Initially, a mild flu-like illness occurs; the illness usually clears up within a few days, but some patients develop more severe symptoms (eg, meningitis, meningoencephalitis). Incidence is highest and severity of disease is greatest in people ≥ 50 years. The case fatality rate and frequency of neurologic sequelae vary by viral subtype (see Centers for Disease Control and Prevention [CDC]: Tick-borne encephalitis; Clinical Evaluation and Disease ).
Tick-borne encephalitis is not a nationally notifiable disease in the United States; however, the CDC reports that 5 cases of tick-borne encephalitis occurred among United States travelers to Europe and China from 2000 through 2011 (2).
Tick-borne encephalitis should be suspected in travelers who have both of the following:
A nonspecific febrile illness that progresses to neuroinvasive disease within 4 weeks after arriving from an endemic area
Risk of tick exposure
The diagnosis of tick-borne encephalitis is usually made serologically by detection of specific IgM antibodies in blood or cerebrospinal fluid, which typically appear only after onset of neurologic manifestations. The virus that causes tick-borne encephalitis can sometimes be detected in serum by virus isolation or reverse transcriptase polymerase chain reaction (RT-PCR) earlier in disease before antibody titers have risen.
As with other viral meningoencephalitides, treatment is supportive.
Prevention of tick-borne encephalitis involves avoiding tick bites. A vaccine is available in some areas where tick-borne encephalitis is endemic (see The European Centre for Disease Prevention and Control [ECDC]: Tick-Borne Encephalitis Recommended Vaccinations). A vaccine is available in the United States for US travelers visiting endemic areas who are at risk of tick exposure (see CDC: Tick-borne encephalitis vaccine).
Powassan virus
In the United States, tick-borne encephalitis is caused mainly by Powassan virus, a flavivirus that is antigenically related to West Nile, St. Louis encephalitis, and tick-borne encephalitis viruses. Powassan virus infections have been reported primarily in the northeastern states and the Great Lakes region. Powassan virus infections in humans have also been reported in southeastern Canada and Russia (southeastern Siberia, northeast of Vladivostok).
In the United States, there are 2 types of Powassan virus, both linked to human disease:
Lineage 1 Powassan virus: Associated with Ixodes cookei or Ixodes marxi ticks
Lineage 2 Powassan virus (sometimes called deer tick virus): Associated with Ixodes scapularis ticks, the same tick that spreads Lyme disease, anaplasmosis, and babesiosis
Lineage 2 Powassan virus infection is more likely than lineage 1 infection because I. cookei ticks rarely bite people.
The time an infected tick must be attached to transmit Powassan virus is probably much shorter (15 minutes) than that needed for Lyme disease (24 to 48 hours) (3).
Although rare, Powassan virus encephalitis appears to be increasing since 2009. A total of 202 cases of Powassan virus disease infection have been reported in the United States from 2012 to 2021, ranging from 7 to 43 cases per year; most (189) were neurologic disease, resulting in 24 deaths. Cases occur in the late spring to mid-fall, when ticks are most active (4).
In the reported cases of Powassan virus infection, neurologic sequelae were common, and the case-fatality rate was high (up to 10 to 15%). This high morbidity and mortality may result from reporting bias because seropositivity in endemic regions is known to be much more common than reported cases, suggesting that there are higher rates of asymptomatic infection.
Powassan virus infection should be considered in patients with encephalitis, especially when the patient has a history of tick bite or spends a lot of time outdoors and lives in or has recently traveled to an endemic area. Diagnosis is similar to that of tick-borne encephalitis, with serologic tests to detect Powassan virus–specific IgM antibody in serum or cerebrospinal fluid and confirmed by neutralizing antibody testing of acute- and convalescent-phase serum specimens at a state public health laboratory or the CDC.
There is no vaccine for Powassan virus infection; the vaccine for tick-borne encephalitis is directed against different flaviviruses and, when one of these tick-borne encephalitis vaccines was tested in mice, it did not prove to be protective against Powassan virus.
People at risk should use personal protective measures to prevent tick bites.
Other tick-borne viruses
Other tick-borne viruses in the United States are
Bourbon virus: This virus was isolated from a single patient who died with multiorgan failure in Bourbon County, Kansas. A limited number of cases have been reported in the southern and midwestern United States.
Heartland virus: As of 2022, there have been more than 60 cases of Heartland virus disease reported from states in the midwestern, northeastern, and southern United States (5). Infection with this virus usually causes a self-limited, nonspecific febrile illness, which may be accompanied by leukopenia. Thrombocytopenia may be present, and liver transferases may be elevated. One patient died. The CDC found signs that the Heartland virus is circulating in deer, raccoons, coyotes, and moose in 13 states, from Texas to North Carolina and Florida to Maine.
Colorado tick fever virus: A coltivirus causes Colorado tick fever. Colorado tick fever has been diagnosed in areas of the western United States and Canada that are 4000 to 10,000 feet (1200 to 3000 meters) above sea level where the vector tick Dermacentor andersoni is located. In the United States, a total of 59 cases were reported to CDC from 2010 through 2019 (6). It causes a nonspecific febrile illness that is rarely complicated by meningitis or encephalitis. Rarely, it is transmitted by blood transfusion.
California encephalitis serogroup viruses
The California encephalitis serogroup viruses, including California encephalitis virus, La Crosse virus, and Jamestown Canyon virus, belong to the Bunyaviridae family. These viruses are transmitted and maintained by Aedes mosquitoes and occur in the Rocky Mountains, eastern United States, southeast Canada, and western Europe.
California encephalitis serogroup viruses cause symptoms (eg, fever, somnolence, obtundation, focal neurologic findings, seizures) primarily in children except for Jamestown Canyon virus, which may also affect adults. Temporal lobe involvement may mimic herpes encephalitis; 20% of patients develop behavioral problems or recurrent seizures.
No treatment is available.
Omsk hemorrhagic fever and Kyasanur Forest disease
Omsk hemorrhagic fever and Kyasanur Forest disease are transmitted by ticks or by direct contact with an infected animal (eg, rodent, monkey). Omsk hemorrhagic fever is caused by a flavivirus; it occurs in Russia, including Siberia. Kyasanur Forest disease, also caused by a flavivirus, occurs in India.
Omsk hemorrhagic fever and Kyasanur Forest disease are acute febrile illnesses accompanied by bleeding diathesis, low blood pressure, leukopenia, and thrombocytopenia; some patients develop encephalitis in the 3rd week. The case fatality rate is < 3% for Omsk hemorrhagic fever and 3 to 5% for Kyasanur Forest disease (7, 8).
Prevention involves avoiding tick bites and infected animals. A vaccine for Kyasanur fever virus is produced in India.
Rift Valley fever
Rift Valley fever, caused by a phlebovirus, is spread by mosquitoes and can be transmitted by the following
Direct or indirect contact with the blood or organs of infected animals (eg, during slaughtering, butchering, or veterinary procedures)
Inhalation of infected aerosols
Ingestion of raw milk from infected animal
Eggs from virus-infected Aedes mosquitoes can contain the virus. Those infected eggs can persist for months to years and, when flooded, can hatch and produce infected adult female mosquitoes capable of transmission.
Rift Valley fever occurs in South Africa, East and West Africa, Arabia, and Egypt (9).
Rarely, Rift Valley fever progresses to ocular disorders, meningoencephalitis, or a hemorrhagic form (which has a 50% case fatality rate). Extensive clusters of abortions may develop in livestock before human cases appear.
A vaccine for livestock is available, and a human vaccine is under investigation.
Arbovirus references
1. World Health Organization: Oropouche virus disease - Peru
2. CDC: Yellow Book: Infectious Diseases Related to Travel: Tickborne Encephalitis
3. Doughty CR, Yawetz S, Lyons J: Emerging causes of arbovirus encephalitis in N America: Powassan, Chikungunya and Zika Viruses. Curr Neurol Neurosci Rep 17:12, 2017. doi 10.1007/s119190-017-724-2
4. CDC: Powassan Virus Statistics and Maps
5. CDC: Heartland virus disease (Heartland) Statistics & Maps
6. CDC: Colorado tick fever (CTF) Statistics & Maps
7. CDC: Omsk Hemorrhagic Fever Signs and Symptoms
8. CDC: Kyasanur Forest Disease Signs and Symptoms
9. CDC: Rift Valley fever Distribution Map
