Overview of Arbovirus, Arenavirus, and Filovirus Infections
Arbovirus, arenavirus, and filovirus are viruses that are spread from animals to people and, with some viruses, from people to people. The animal involved depends on the type of virus.
Many of these infections do not cause symptoms. Symptoms of most of these infections, when they occur, are usually mild and vague and resemble flu symptoms. As the infection progresses, people may have swollen lymph glands, rashes, and joint pain. Some of these viruses can infect the tissues that cover the brain and spinal cord (meningitis) or the brain (encephalitis). Some cause fever with a tendency to bleed easily (called hemorrhagic fever), which can be life threatening.
Arbovirus stands for arthropod-borne virus. An arbovirus is not a single type of virus. Scientists apply the name arbovirus to over 250 different viruses from many different families of virus that are spread to people or animals by certain arthropods that feed on blood, mainly insects (flies and mosquitoes) and ticks. At least 80 arboviruses cause disease in people.
Arboviruses are spread when an insect or tick bites an infected animal or person, then bites another person or animal. Most arbovirus infections are not spread from person to person. Exceptions include chikungunya disease and the flavivirus infections dengue, yellow fever, and Zika virus infection, which can be transmitted from person to person by mosquitoes. Also, Zika virus can be spread during sexual activity. Uncommonly, dengue, chikungunya, and Zika viruses have been spread by blood transfusion or organ donation or from mother to newborn at birth. Casual, everyday contact has not been shown to transmit arboviruses from person to person.
Many arboviruses that were once present in only a few parts of the world are now spreading. These viruses include chikungunya virus, Crimean-Congo hemorrhagic fever virus, Japanese encephalitis virus, Rift Valley fever virus, West Nile virus, Ross River virus, and Zika virus. These viruses are spreading partly because climate change has resulted in more areas where the mosquitoes that spread the viruses can live. Also, travelers may be infected in areas where the virus is common, then return home and be bitten by a mosquito, which spreads the virus to other people.
Chikungunya virus is spread by a certain species of mosquito called the Aedes mosquito. This virus was first identified in Africa but has recently spread to the Caribbean and Central, South, and North America. Chikungunya virus infection typically causes a fever and severe joint pain, often in the hands and feet. Infected people may also have a headache, muscle pain, joint swelling, or a rash. Most people feel better within a week, but joint pan can persist for months or sometimes even years.
Arenaviruses are spread by rodents. Infections caused by these viruses include lymphocytic choriomeningitis, Lassa fever, Bolivian hemorrhagic fever (caused by Machupo virus), Venezuelan hemorrhagic fever (caused by Guanarito virus), and Argentine hemorrhagic fever (caused by the Junin virus). Lassa fever can also be spread from person to person. Arenavirus infections are relatively common in people in some areas of the world and can cause severe disease.
Filoviruses can cause severe hemorrhagic fever in people and other primates (such as apes and monkeys). So far, only two members of this group of viruses have been identified:
How these viruses first spread to people has not been identified. However, experts think that the first person was infected by handling or eating an infected animal, such as a fruit bat or primate. These viruses spread readily from person to person.
To diagnose these infections, doctors may do blood tests and cultures. Blood may be tested for antibodies to or antigens of a virus. (Antibodies are proteins produced by the immune system to help defend the body against a particular attack. Antigens are proteins on or in viruses that trigger the body’s defenses.) Culture involves growing microorganisms in the laboratory from samples of blood, body fluid, or other material taken from an infected area until there are enough to identify.
Polymerase chain reaction (PCR) techniques may be used to make many copies of the virus's genetic material. This technique enables doctors to rapidly and accurately identify the virus.
Tests are sometimes done quickly—for example, when the infection is a serious threat to public health or when symptoms are severe.
A sample of blood or other tissues is sometimes examined with an electron microscope, which provides high magnification with clear resolution.
Because there are so many different arboviruses, it is often easier and cheaper to control arbovirus infections by controlling the arthropods that spread them and preventing exposure to the virus (including preventing mosquito and tick bites) than by developing specific vaccines or drug treatments.
Controlling mosquitoes is difficult, but new approaches are being developed and tested. In addition to using chemical pesticides, scientists are genetically modifying mosquitoes, releasing sterilized male mosquitoes into the environment, or infecting mosquitoes with a bacteria that blocks virus infection in the mosquitoes.
Infections spread by mosquitoes or ticks can often be prevented by the following:
For example, to help prevent mosquito bites, people can limit the time they spend outdoors in wet areas.
For ticks, the following can help:
Staying on paths and trails
Tucking trousers into boots or socks
Wearing long-sleeved shirts (see sidebar Tick Bite Prevention)
Infections spread by mice or other rodents usually result from exposure to their urine, feces, or another body fluid, which contains the virus. The following can help prevent such exposure:
Prevention of exposure to Ebola or Marburg virus requires strict quarantine of infected people and use of isolation measures, because these viruses spread readily from person to person.
At present, effective vaccines for people are widely available, including in the United States, only for Ebola, yellow fever virus, and Japanese encephalitis virus. Vaccines for tick-borne encephalitis are available in Europe, Russia and China. A vaccine for dengue is available in several countries outside the United States, but it is only somewhat effective and is given only to people who had a prior dengue infection.
Treatment of most of these infections focuses on relieving symptoms and maintaining vital functions. For example, transfusions may be given if bleeding is severe.
The antiviral drug ribavirin may be used to treat hemorrhagic fever, as may occur in Lassa fever.