TOGAVIRUS DISEASES AND CLINICAL PRESENTATION
There is only one virus in the rubivirus genus, the only non arthropod-borne virus of the togaviridae.
Rubella infections usually occur during the winter and spring months. Infections are often asymptomatic or very mild with only 30-60% of infected individuals developing clinically apparent disease. Adult infections are especially subclinical. Symptoms of infection may include: mild fever, sore throat, coryza, cough, upper respiratory symptoms, lymphadenopathy, red maculopapular rash that appears on face and spreads down body, mild arthralgia, arthritis, placentitis, and fetal damage (with congenital rubella syndrome). The clinical manifestations of rubella in children are generally less severe than those caused by measles. The virus has the potential to cross placenta and multiply in the fetus. The major concerns about rubella infection are due to the harmful effects of congenital rubella syndrome (CRS). Up to 85% of infants infected with rubella virus in the first trimester of pregnancy get congenital rubella syndrome. Congenital rubella syndrome may result in: low birth weight, deafness, cardiac defects, eye defects, enlargement of the liver and spleen, anemia, disruption of the central nervous system, encephalitis, mental retardation, complications that develop later in the child's life, and abortion of the fetus. The earlier in pregnancy infection occurs, the worse the risks associated with infection.
Image Courtesy of the CDC Rubella Web Page http://www.cdc.gov/ncidod/dvbid/rubella/baby.htm
There is currently no antiviral treatment for rubella infection, but there is a vaccine. The rubella vaccine is a live attenuated vaccine that has been available since 1969. It is effective at causing seroconversion in about 95% of patients vaccinated. It is usually administered as part of the Measles, Mumps, and Rubella combination vaccine. It is not recommended that the vaccine be administered to pregnant women or women who are anticipating conception.
The alphaviruses are significant causes of viral encephalitis. Symptoms of encephalitis are drowsiness, stiff neck, disorientation, convulsions, tremors, coma, and, in some cases, death. The alphaviruses are transmitted to humans by an arthropod vector, usually mosquitoes. Alphavirus infections usually occur during warm weather months when mosquitoes are more active and prevalent. Anyone can be infected, but young children and elderly are generally most susceptible to alphavirus infection. The virus grows in both the insects (i.e. mosquitoes) and the mammals (i.e. birds, horses, humans) infected, but are only known to produce cytopathic effects in the mammalian hosts. The mechanism by which this occurs is not yet understood. When the mosquito vector bites the vertebrate host, the virus is transmitted from the salivary glands of the mosquito to the bloodstream of the vertebrate host. The alphavirus travels to the skin and reticuloendothelial system (spleen and lymph nodes), where the primary infection occurs. This stage is followed by viremia. The infection often affects the central nervous system (i.e. in cases of encephalitis), the skin, bone marrow, and blood vessels. Depending on the specific virus, incubation periods range from 1 day to about 3 weeks.
Photo Courtesy of the BBC World News website http://news.bbc.co.uk/2/hi/south_asia/2174374.stm
SINDBIS VIRUS (SIN)
The infection is often asymptomatic or dismissed as a minor flu-like illness. Symptoms may include: fever, myalgia, arthritis, headache, and an exanthem which appears first on trunk of host and progresses to extremities. Less common symptoms include: jaundice and myocardial damage. SIN is transmitted by a mosquito vector. Sindbis virus infection affects regions of Africa, Asia, Australia, the Middle East, and Eastern Europe.
Initial symptoms of infection may include: fever, myalgia, a headache of increasing severity, and other mild flu-like symptoms. In some cases, encephalitis (inflammation of the brain) develops and symptoms progress to include: seizures, coma, and death. Depending on the source, mortality estimates for EEE range from 35% to 50%. Of those who do survive EEE infection, around 35% will have mild to severe sequelae (often neurologic defects). EEE is transmitted by a mosquito vector that feeds primarily on horses and birds but occasionally will spread the virus to humans. EEE occurs in regions along the Atlantic coast of North America, especially affecting the eastern United States.
Most infections are asymptomatic or appear as a mild, nonspecific illness. Generally, only 0.1% of infections are clinical, but in infants, the rate of severe illness is much higher. Initial symptoms of infection may include: fever, headache, nausea, vomiting, anorexia, and malaise. Clinical manifestations may progress to include: altered mental state, persistent fatigue, aseptic meningitis, encephalitis, coma, and death. At only 2-5%, WEE has a much lower mortality rate than EEE. 60% of infant infections result in permanent neurologic damage. WEE is transmitted by a mosquito vector. The virus affects regions of the western United States.
Symptoms of infection may include: fever, chills, severe headache, myalgia, and other flu-like symptoms. Infection may progress to cause: leucopenia, persistent fatigue, paralysis, and encephalitis, which is more likely to develop in children than in adults. Encephalitis associated symptoms include: disorientation, convulsions, paralysis, coma, and death. Some studies have found men to be more susceptible to infection than women. A study done in Texas in 1971 reported a 2:1 ratio of male to female cases of VEE. The mortality rate for VEE is generally low for healthy adults, but varies; some sources report a mortality rate ranging as high as 70%. Overall, VEE virus infection is less severe than those of EEE and WEE viruses, and fatalities are not common. WEE is transmitted by a mosquito vector. The virus affects regions of Southern US, Central America, and South America.
This virus is a variant strain of Venezuelan equine encephalitis. It has not been known to cause disease in humans. EVE is carried by mosquitoes. This strain is specific to the Everglades region of Southern Florida.
Symptoms of infection may include: mild fever, maculopapilar exanthem, and arthralgia, or arthritis of the small joints of the extremities. Ross River virus is transmitted by a mosquito vector. It affects regions of Australia, New Guinea, and the Pacific Islands.
Symptoms of infection may include: arthritic symptoms (similar to those of Ross River virus infection). Barmah Forest virus is transmitted by a mosquito vector. It affects regions of eastern Australia, especially the state of Queensland.
This virus often results in inapparent infection. Symptoms of infection may include: high fever, maculopapular rash, nausea, vomiting, arthralgia or arthritis of the small joints of the extremities, and mild hemorrhaging (especially in children). CHIK is transmitted by a mosquito vector. The chikungunya virus affects regions of Africa and Asia.
Infections by Mayaro virus are commonly inapparent. Symptoms of infection may include: fever, arthralgia or arthritis of small joints of the extremities, and development of a maculopapular rash. Mayaro virus is transmitted by a mosquito vector. This virus is known to affect regions of Central America and South America.
ONN virus infection is commonly inapparent. Symptoms of infection may include: fever, arthralgia or arthritis of small joints of the extremities, and development of a maculopapular rash (occurs in 60-70% of infections). ONN virus is transmitted by a mosquito vector. This virus is known to affect regions of Africa.
Mims, Playfair, Roitt, Wakelin, Williams. Medical Microbiology, Second Edition. Mosby Publishers Limited, New York: 1998.
Centers for Disease Control and Prevention
http://www.cdc.gov/ncidod/dvbid/arbor/arbdet.htm
http://www.cdc.gov/ncidod/dvbid/arbor/arboguid.pdf
http://www.cdc.gov/ncidod/dvbid/arbor/mosqfeed.htm
http://www.who.int/csr/delibepidemics/en/annex3May03.pdf
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Canada Office of Laboratory Security: Material Safety Data Sheets http://www.hc-sc.gc.ca/pphb-dgspsp/msds-ftss/index.html