History
Bites
The patient may give a history of arthropod bites, including ticks, mosquitoes, gnats, and midges. In cases of Oklahoma tick fever or Kemerovo or Lipovnik virus infections, a tick transmits the virus. Orbiviral infections in Africa and South America may be spread via mosquito bites.
Although incubation time from exposure to clinical illness is unknown in humans, it has been estimated at 6-9 days in animals.
Based on serologic studies, orbiviral infections often are asymptomatic or present as a mild nonspecific febrile illness for which medical care is not sought. Patients who present for medical evaluation often report fever, myalgia, nausea, vomiting, diarrhea, and confusion. Seizures and, rarely, focal neurologic deficits may also develop.
Travel/geographic considerations
History is significant for travel to a location that contains an orbiviral reservoir (ie, Russia, Eastern Europe, Africa, South America, Central America, the states of Texas and Oklahoma).
Russia and Eastern Europe
The Kemerovo antigenic complex includes the Kemerovo, Lipovnik, and Tribec viruses. These are tick-borne (specifically Ixodes ticks) orbiviruses that are found in Russia and Eastern Europe.
This group of viruses is the suspected cause of 12 cases of encephalitis in the Kemerovo region of Russia. [7] In addition, meningoencephalitis and, perhaps, polyradiculitis have been linked to the Lipovnik virus in the former Czechoslovakia.
Central and West Africa
Orungo virus is an Orbivirus found in parts of sub-Saharan Africa. This virus is thought to cause asymptomatic infection; however, it has been linked to acute illnesses characterized by fever, headache, and myalgia. This virus also is implicated in a case of encephalitis in a child.
A study has shown a high rate of co-infection with yellow fever and Orungo viruses, possibly due to their similar geographic distribution and their common use of Aedes mosquitoes as the principal vector. [8] Although the principal vector is Aedes, anopheline and Culex mosquitoes also are implicated in transmission. [9]
South Africa and Nigeria
Lebombo virus is also found in parts of Africa, specifically South Africa and Nigeria.
It has been isolated from Aedes and Mansonia mosquitoes and from rodents.
A single human case involving a Nigerian child (with fever) has been reported. [10]
South America
Changuinola virus is linked to a single documented case of an acute self-limited febrile illness in Panama. However, the seroprevalence of this disease is high in parts of South America; thus, the true extent or frequency of this infection currently is unknown. [11]
Transmission is most likely by Phlebotomus flies.
China
There have been no documented human cases. A study from Guangdong found a novel orbivirus in the pooled Culex fatigans mosquitoes, which was named the Fengkai virus. It is hypothesized that this virus has the potential to infect humans and can be severely pathogenic. [30]
United States
Several cases of human disease have been reported in Oklahoma and Texas; the disease is now named Oklahoma tick fever. The disease is considered a new arboviral disease in the western United States that is related to the Kemerovo serogroup of orbiviruses.
Patients presented with prostrating grippes, nausea, abdominal pain, and fever. Several patients had concomitant cytopenia (transient thrombocytopenia, anemia, and/or leukopenia). Each patient recalled tick exposure; however, the specific causative tick is currently unknown.
Researchers observed a 4-fold rise in the immunofluorescent antibodies to Lipovnik and Six Gun City viruses and the absence of seroreactivity to Rocky Mountain spotted fever, Colorado tick fever, and Powassan virus. Because the causative virus was never isolated, the exact etiology remains unknown, although researchers suspect an Orbivirus. Consider orbiviruses within the differential of a suspected viral or rickettsial infection in the southwestern United States.
In the midwestern United States, Kemerovo-related viruses are known to cause infections in rabbits and large animals, but no human cases have been reported.
Physical
Physical findings vary depending on the specific Orbivirus involved; however, the most common physical finding is fever.
Other nonspecific symptoms have been reported, including headache, myalgia, and gastrointestinal problems.
Patients may be encephalopathic or may demonstrate focal neurologic findings.
Causes
Risk factors include travel to an area with known orbiviruses, particularly Texas and Oklahoma. Overseas travel to Russia, Eastern Europe, South America, Central America, and Africa may also lead to orbiviral exposure.
Outdoor activity is the best-known risk factor because disease transmission to humans is via arthropod vectors. The seasonality of the infection relates to the time of arthropod activity.
Aside from arthropod-borne transmission, 4 workers in South Africa were infected with lyophilized virus in a veterinarian's office (1989). The vaccine contained neurotropic attenuated strains of African horse sickness virus. Three developed frontotemporal encephalitis, and all 4 developed uveochorioretinitis. Cases were diagnosed serologically. No naturally occurring human infections have been reported with the African horse sickness viruses.
