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. 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 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.
- 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 seem 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.
Hemorrhagic fever with renal syndrome (HFRS)
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.
After about five days, the patient may have a sudden drop in blood pressure; often it drops low enough to cause the clinical syndrome called shock. Shock is a state in which blood circulation throughout the body is insufficient to deliver proper quantities of oxygen. Lengthy shock can result in permanent damage to the body's organs, particularly the brain, which is very sensitive to oxygen deprivation.
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.
Day eleven often brings further chemical derangements, with associated confusion, hallucinations, seizures, and lung complications. Those who survive this final phase usually begin to turn the corner towards recovery at this time, although recovery takes approximately six weeks.
Hantavirus pulmonary syndrome (HPS)
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, headache, dizziness, 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 patient's blood is drawn, and the ELISA (enzyme-linked immunosorbent assay) is done in a laboratory to identify the presence of specific immune substances (antibodies)—substances which an individual's body would only produce in response to the hantavirus.
It is very 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. Broad-spectrum antibiotics are given until the diagnosis is confirmed. Supportive care consists of providing treatment in response to the patient's symptoms. Because both HFRS and HPS progress so rapidly, patients must be closely monitored, so that treatment may be started at the first sign of a particular problem. Low blood pressure is treated with medications. Blood transfusions are given for both hemorrhage and shock states. Hemodialysis is used in kidney failure. (Hemodialysis involves mechanically cleansing the blood outside of the body, to replace the kidney's normal function of removing various toxins form the blood.) Rapid respiratory assistance is critical, often requiring intubation.
The diseases caused by hantaviruses are extraordinarily 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.
There are no immunizations currently available against any of the hantaviruses. The only forms of prevention involve rodent control within the community and within individual households. The following is a list of preventative measures:
- Avoiding areas known to be infested by rodents is essential.
- Keep a clean home and keep food in rodent-proof containers.
- Dispose of garbage and empty pet food dishes at night.
- Set rodent traps around baseboards and in tight places. Dispose of dead animals with gloves and disinfect the area with bleach.
- Use rodenticide as necessary.
- Seal any entry holes 0.25 inch wide or wider around foundations with screen, cement, or metal flashing.
- Clear brush and junk from house foundations.
- Put metal flashing around house foundations.
- Elevate hay, woodpiles, and refuse containers.
- Air out all sealed outbuildings or cabins 30 minutes before cleaning for the season.
- When camping, do not sleep on the bare ground; sleep on a cot or in a tent with a floor.
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Monroe, Martha C., Sergey P. Morzunov, Angela M. Johnson, Michael De. Bowen, et al. "Genetic Diversity and Distribution of Peromyscus-Borne Hantaviruses in North America." Nursing (January-February 1999): 75-86.
Naughton, Laurie. "Hantavirus Infection in the United States: Are We Prepared?." Physician Assistant (May 2000): 33.
Rhodes III, Luther V., Cinnia Huang, Angela J. Sanchez, Stuart T. Nichol, et al. "Hantavirus Pulmonary Syndrome Associated with Monongahela Virus, Pennsylvania." Emerging Infectious Diseases (November 2000): 616.
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Centers for Disease Control and Prevention. (404) 332-4559. <http://www.cdc.gov/travel/travel.html>.
Janie F. Franz
Hemodialysis—A method of mechanically cleansing the blood outside of the body, in order to remove various substances which would normally be cleared by the kidneys. Hemodialysis is used when an individual is in relative, or complete, kidney failure.
Hemorrhagic—A condition resulting in massive, difficult-to-control bleeding.
Petechiae—Pinpoint size red spots caused by hemorrhaging under the skin.
Platelets—Circulating blood cells which are crucial to the mechanism of clotting.
Prodrome—Early symptoms or warning signs
Pulmonary—Referring to the lungs.
Renal—Referring to the kidneys.
Shock—Shock is a state in which blood circulation is insufficient to deliver adequate oxygen to vital organs.