Hantavirus and Hanta disease

Hantavirus (family Bunyaviridae, genus Hantavirus) infection is caused by viruses that can infect humans with two serious illnesses: hemorrhagic fever with renal syndrome (HFRS), and Hantavirus pulmonary syndrome (HPS).

Hantaviruses are found without causing symptoms within various species of rodents and are passed to humans by exposure to the urine, feces, or saliva of those infected rodents. Infection is commonly associated with disturbing the droppings or nests of rodents within confined spaces. The disturbed particles are inhaled to cause infection. Ten different hantaviruses have been identified as important in humans. Each is found in specific geographic regions, and therefore is spread by different rodent carriers. Further, each type of virus causes a slightly different form of illness in its human hosts. Hantaan virus is carried by the striped field mouse, and exists in Korea, China, Eastern Russia, and the Balkans. Hantaan virus often causes a severe form of hemorrhagic fever with renal syndrome (HFRS).

Puumula virus is carried by bank voles, and exists in Scandinavia, western Russia, and Europe. Puumula virus causes a milder form of HFRS, usually termed nephropathia epidemica.

Seoul virus is carried by a type of rat called the Norway rat, and exists worldwide, but causes disease almost exclusively in Asia. Seoul virus causes a form of HFRS which is slightly milder than that caused by Hantaan virus, but results in liver complications.

Prospect Hill virus is carried by meadow voles and exists in the United States, but has not been found to cause human disease. Sin Nombre virus, the most predominant strain in the United States, is carried by the deer mouse. This virus was responsible for severe cases of HPS that occurred in the Southwestern United States in 1993. A similar, but genetically distinct strain was responsible for an outbreak of HPS in Argentina in 1996, and was later termed the Andes virus. During the outbreak in Argentina, five of the victims were physicians, three of which were directly responsible for the care of an HPS patient. This, along with additional epidemiologic evidence (such as the low rodent population density in the area affected) suggest that person-to-person transmission was possible during this outbreak, a feature unique to any known hantavirus.

Black Creek Canal virus has been found in Florida. It is predominantly carried by cotton rats. New York virus strain has been documented in New York State. The vectors for this virus appear to be deer mice and white-footed mice. Bayou virus has been reported in Louisiana and Texas and is carried by the marsh rice rat.

Blue River virus has been found in Indiana and Oklahoma and seems to be associated with the white-footed mouse. Monongahela virus, discovered in 2000, has been found in Pennsylvania and is transmitted by the white-footed mouse.

Hantaviruses that produce forms of hemorrhagic fever with renal syndrome (HFRS) cause a classic group of symptoms, including fever, malfunction of the kidneys, and low platelet count. Because platelets are blood cells important in proper clotting, low numbers of circulating platelets can result in spontaneous bleeding, or hemorrhage.

Patients with HFRS have pain in the head, abdomen, and lower back, and may report bloodshot eyes and blurry vision. Tiny pinpoint hemorrhages, called petechiae, may appear on the upper body and the soft palate in the mouth. The patient's face, chest, abdomen, and back often appear flushed and red, as if sunburned. Around day eight of HFRS, kidney involvement results in multiple derangements of the body chemistry. Simultaneously, the hemorrhagic features of the illness begin to cause spontaneous bleeding, as demonstrated by bloody urine, bloody vomit, and in very serious cases, brain hemorrhages with resulting changes in consciousness and shock.

Hantavirus pulmonary syndrome (HPS) develops in four stages. They are: The incubation period. This lasts from one to five weeks from exposure. Here, the patient may exhibit no symptoms.

The prodrome, or warning signs, stage. The patient begins with a fever, muscle aches, backache, and abdominal pain and upset. Sometimes there is vomiting and diarrhea.

The cardiopulmonary stage. The patient slips into this stage rapidly, sometimes within a day or two of initial symptoms; sometimes as long as 10 days later. There is a drop in blood pressure, shock, and leaking of the blood vessels of the lungs, which results in fluid accumulation in the lungs, and subsequent shortness of breath. The fluid accumulation can be so rapid and so severe as to put the patient in respiratory failure within only a few hours. Some patients experience severe abdominal tenderness.

The convalescent stage. If the patient survives the respiratory complications of the previous stage, there is a rapid recovery, usually within a day or two. However, abnormal liver and lung functioning may persist for six months.

The diagnosis of infection by a hantavirus uses serologic techniques. The ELISA (enzyme-linked immunosorbant assay ) is done in a laboratory to identify the presence of specific immune substances (antibodies), which an individual's body would only produce in response to the hantavirus. It is difficult to demonstrate the actual virus in human tissue or to grow cultures of the virus within the laboratory, so the majority of diagnostic tests use indirect means to demonstrate the presence of the virus.

Treatment of hantavirus infections is primarily supportive, because there are no agents available to kill the viruses and interrupt the infection. The diseases caused by hantaviruses are lethal. About 6–15% of people who contract HFRS have died. Almost half of all people who contract HPS will die. It is essential that people living in areas where the hantaviruses exist seek quick medical treatment, should they begin to develop an illness that might be due to a hantavirus. Preventative measures focus on vector control (elimination of rodents), and avoiding rodent infested areas.

See also Epidemics, viral; Epidemiology, tracking diseases with technology; Epidemiology; Hemorrhagic fevers and diseases; Virology