Hantavirus pulmonary syndrome (HPS) is an infectious disease caused by the Sin Nombre hantavirus. Transmission occurs when direct or indirect (airborne) contact is made with the saliva or waste products of rodents that carry the virus, most commonly the deer mouse (Peromyscus maniculatus). Initial symptoms may include fever, muscle aches (myalgias), headache, cough, and/or difficulty breathing. Symptoms progress rapidly, and abnormally low blood pressure (hypotension), shock, and/or respiratory failure may occur.
The initial symptoms of HPS most commonly include fever, muscle aches (myalgias), headache, and/or cough. Chills, abdominal pain, diarrhea, and/or a sense of overall discomfort (malaise) may be present. Other symptoms usually include shortness of breath, rapid breathing (tachypnea), rapid heartbeat (tachycardia), dizziness, and sometimes joint pain (arthralgia), back and/or chest pain, and/or sweating.
Shortly after the initial symptoms of HPS appear excess fluid may accumulate in the lungs (pulmonary edema), beginning in the air spaces in the lungs (interstitial edema). Fluid may then fill the pockets in the lung tissue (alveolar edema) of both lungs (bilaterally) and cause difficulty in breathing and abnormally low levels of oxygen in the blood (hypoxemia). Accumulation of tissue and cells not normally found in the lungs (infiltrates) may also occur. The disease progresses rapidly and may cause abnormally low blood pressure (hypotension), shock, and/or respiratory distress.
HPS is caused by Sin Nombre Hantavirus, a newly identified virus within the Bunyaviridae family. The virus is carried by rodents, most commonly by the deer mouse (Peromyscus maniculatus). The deer mouse can be found in most parts of the United States, except the southeast. Not all deer mice are infected with Sin Nombre hantavirus, and those that do carry the virus do not appear to be affected by any associated disease.
Another strain of the Hantavirus has been identified in the white-footed mouse which is a species native to the eastern US. This strain has been named New York virus. In addition, another new strain was identified in harvest mice found in Orange County, CA, and Arizona’s Apache County. Harvest mice are found from southern Alberta, Canada, into north-central Mexico and from California to Wisconsin.
Sin Nombre hantavirus is transmitted to humans when they come in direct or indirect (airborne) contact with waste products or saliva from an infected rodent. Respiratory transmission, thought to be the most frequent mode of transmission of Sin Nombre hantavirus, occurs when an individual inhales airborne particles of dust or dried particles that carry saliva or waste products from an infected rodent. Infectious virus particles could also penetrate through the mucosa.
HPS appears to affect males and females in equal numbers. Approximately half of the cases reported in the medical literature have affected Native Americans, and the majority of the remaining reported cases affected Caucasians. The population affected by HPS appears to be related to geographic location and exposure to rodent droppings as opposed to ethnic background. Because many of the documented cases have occurred in the southwestern United States, a high percentage of the initially affected individuals were Native Americans. As the virus was found in others parts of the US, many others of varied ethnic backgrounds have been affected throughout the United States.
It is important to avoid areas where deer mice leave their droppings, such as storage sheds, basements, and wood piles. When exposed to mouse droppings, an individual should wear a face mask that covers both nose and mouth, as well as rubber gloves. The area should be sanitized with disinfectant. People who exhibit flu-like symptoms after exposure to mouse droppings should be taken to a hospital immediately, because this disorder progresses over a matter of hours, and every hour is crucial.
The diagnosis of HPS depends on several factors, including the symptoms of the affected individual, a history of contact with rodents (especially deer mice) or exposure to areas where rodents may live, the lack of any alternative diagnosis, and/or laboratory tests that show characteristic changes. Because the symptoms of HPS are rapidly progressive, immediate aggressive care is indicated if HPS is suspected.
Characteristic laboratory blood test results for people with HPS may show abnormally enlarged white blood cells (atypical lymphocytes), a platelet count that is lower than normal (thrombocytopenia) or dropping, and/or a higher than normal white blood cell count. Oxygen levels in blood and/or tissue may be extremely low (hypoxemia).
The diagnosis of HPS is confirmed when laboratory tests reveal the presence and/or increased levels of certain proteins (Hantavirus IgM and/or a rising IgG titer) in blood samples from affected individuals. A process called polymerase chain reaction (PCR) may be used to detect a hantavirus and identify which strain has caused the infection.
Treatment of HPS involves intensive care, including the monitoring of fluid balances, electrolyte balances, and blood pressure. Abnormally low levels of oxygen in the blood (hypoxemia) may require the administration of oxygen. Shock and low blood pressure (hypotension) associated with HPS may be treated with drugs (i.e., dopamine and norepinephrine) to increase blood flow and thus improve blood and oxygen delivery to organs.
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