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Hantavirus
Hantavirus pulmonary syndrome (HPS) is a pan-American viral zoonosis caused by Sin Nombre virus and other New World hantaviruses which, in the United States, include Bayou virus, Black Creek Canal
virus, and New York-1 virus. Hantaviruses are maintained in a select group of rodents around the world. When people are infected,
the results vary from mild flu-like illness to death, depending on several factors including the strain of virus. In the spring and summer of 1993, there was an outbreak of acute respiratory distress with a high
fatality rate (  70%) among previously healthy individuals. Mortality was traced to infection with a
previously unrecognized hantavirus [6] that was transmitted by a common native field rodent, the deer mouse [4]. This discovery is significant because the rodent is widely distributed throughout North
America, ranging from the Arctic circle to the Mexican Plateau and from the Pacific Ocean to the Eastern United States. Surveys show that the virus is widespread throughout the range of the rodent;
thus, most individuals residing in rural areas of North America are potentially at risk for this disease. Consequently, the question arose as to why outbreaks had not been previously recognized.
The identified rodent reservoirs for Sin Nombre, New York-1, Black Creek Canal, and Bayou viruses are Peromyscus maniculatus (deer mouse), Peromyscus leucopus (white-footed mouse), Sigmodon hispidus
(cotton rat), and Oryzomys palustris (rice rat), respectively. Cases of HPS have been identified in the continental United States, Canada, Argentina, Brazil, Chile, Paraguay, and Uruguay. As
of May 1, 1997, national surveillance for HPS has identified 160 confirmed cases in 26 states, among which the overall case fatality rate is 47.5%. 22 of the 160 cases occurred during 1996.
Recent work suggests that climatic conditions associated with an El Nino event led to conditions favoring increased rodent populations through the spring of 1993 so that rodent populations in the area
of the outbreak reached record levels [7]. This was thought to be due to the above average
precipitation patterns in the region, leading to increased rodent survival and reproduction during the summer and autumn of 1992, a time when rodent populations usually decline in response to arid
conditions. An epidemiologic analysis of residences of households associated with hantavirus showed that these sites were associated with higher abundance of infected deer mice than houses with no cases of hantavirus [3].
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