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Other Arbovirus Infections
(See also Overview of Arbovirus, Arenavirus, and Filovirus Infections.)
This disease is an acute febrile illness followed by more chronic polyarthritis. It is transmitted by Aedes mosquitoes and is common in Africa, India, Guam, Southeast Asia, New Guinea, China, Mexico, Central America, islands in the Caribbean, Indian Ocean and Pacific, and limited areas of Europe. Local transmission has been identified in Florida, Puerto Rico, and the US Virgin Islands.
Prevention of chikungunya disease involves avoiding mosquito bites.
Tick-borne encephalitis (TBE) is caused by a flavivirus that has 3 subtypes, European, Siberian, and Far Eastern.
TBE is transmitted to humans in focal areas extending from eastern France to northern Japan by the bite of infected hard–bodied ticks, in Europe and in Siberia and the Far East. Ticks are both vector and virus reservoir, and small rodents are the primary amplifying host. TBE 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 about 30% of patients develop more severe symptoms (eg, meningitis, meningoencephalitis). Incidence is highest and severity of disease is greatest in people ≥ 50 yr.
TBE is not a nationally notifiable disease in the US; however, the CDC reports that 5 cases of TBE occurred among US travelers to Europe and China from 2000 through 2011 (1.).
TBE should be suspected in travelers who have both of the following:
The diagnosis of TBE is usually made serologically by detection of specific IgM antibodies in blood or CSF, which typically appear only after onset of neurologic manifestations. Although TBE virus can sometimes be detected in serum by virus isolation or reverse transcriptase PCR (RT-PCR) earlier in disease before antibody titers have risen.
As with other viral meningoencephalitides, treatment is supportive.
Although no TBE vaccines are licensed or available in the US, there are several effective inactivated TBE vaccines available in Russia, Europe, and Canada. Vaccination is recommended for people who work outdoors or engage in recreational activities in endemic areas and are at risk of tick exposure.
In the US, tick-borne encephalitis is caused mainly by Powassan virus (POWV), a flavivirus that is related to West Nile, St. Louis encephalitis, and TBE viruses. POWV infections have been reported primarily in the northeastern states and the Great Lakes region. POWV infections in humans have also been reported in Canada and Russia (southeastern Siberia, northeast of Vladivostok).
In the US, there are 2 types of Powassan virus, both linked to human disease:
Lineage 2 POWV infection is more likely than lineage 1 infection, because ticks rarely bite people.
The time an infected tick must be attached to transmit POWV is probably much shorter (15 min) than that needed for Lyme disease (24 to 48 h [2, 3]).
Although rare, POWV encephalitis appears to be increasing since 2006 (4). About 75 cases of POWV disease infection have been reported in the US over the past 10 yr (5). Cases occur in the late spring to mid-fall, when ticks are most active.
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.
POWV should be considered in patients with encephalitis, especially when the patient has a history of tick bite or spends a lot of time outdoors. Diagnosis is similar to that of TBE, with serologic tests to detect POWV-specific IgM antibody in serum or CSF and confirmed by neutralizing antibody testing of acute- and convalescent-phase serum specimens at a state public health laboratory or CDC.
There is no vaccine for POWV infection; the vaccine for TBE available outside the US is directed against different flaviviruses and, when one of these TBE vaccines was tested in mice, has did not prove to be protective against POWV.
People at risk should use personal protective measures to prevent tick bites.
Other tick-borne viruses in the US are
Bourbon virus: This virus was isolated from a single patient who died with multiorgan failure in Bourbon County, Kansas.
Heartland virus: This virus was isolated in 8 cases in Missouri and Tennessee). It usually causes a self-limited, nonspecific febrile illness; (although 1 patient died).
Colorado tick fever virus: A coltivirus causes Colorado tick fever. Colorado tick fever has been diagnosed in areas of the western US and Canada that are 4,000 to 10,000 feet above sea level. It causes a nonspecific febrile illness that is rarely complicated by meningitis or encephalitis. Rarely, it is transmitted by blood transfusion.
The California encephalitis virus belongs to the Bunyaviridae family. This encephalitis and related infections are transmitted by mosquitoes and occur in the US Midwest and probably worldwide.
California encephalitis causes symptoms (eg, fever, somnolence, obtundation, focal neurologic findings, seizures) primarily in children. Temporal lobe involvement may mimic herpes encephalitis; 20% of patients develop behavioral problems or recurrent seizures. Mortality rate is < 1%.
No treatment is available.
These infections 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 BP, leukopenia, and thrombocytopenia; some patients develop encephalitis in the 3rd wk. Mortality rate is < 3% for Omsk hemorrhagic fever and 3 to 5% for Kyasanur Forest disease.
Prevention involves avoiding tick bites and infected animals.
This infection, caused by a phlebovirus, is spread by mosquitoes and can be transmitted by the following:
Rift Valley fever occurs in South Africa, East and West Africa, Arabia, and Egypt.
Rarely, Rift Valley fever progresses to ocular disorders, meningoencephalitis, or a hemorrhagic form (which has a 50% mortality rate).
A vaccine for livestock is available, and a human vaccine is under investigation.
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