Rodents infected with hantaviruses excrete the virus in their urine and feces, and secrete the virus in saliva (ref,ref). Although it is frequently stated that hantaviruses are transmitted from mouse to man through aerosols of contaminated rodent excreta, the evidence supporting these claims is rather weak and indirect. The strongest evidence comes from cases in Russia, Korea and Japan wherein persons who apparently made only brief, casual visits to laboratories containing Seoul or Puumala virus-infected rodents became ill with hemorrhagic fever. However, it is inherently difficult to document this route of infection with great confidence. In recent years, evidence of person-to-person transmission of Andes hantavirus has emerged in Argentina (ref). Person-to-person transmission is especially troubling because no clear mechanism for this transmission has been identified. It has not been reported in North America, Asia, or Europe. Fortunately, molecular epidemiology offers a powerful tool to support or refute specific models of hantavirus transmission and might someday be used to identify the specific routes of interpersonal transmission for Andes virus (ref).
HCPS is associated with a number of newly-identified hantavirus species: Sin Nombre, New York, Bayou, and Black Creek Canal viruses in the US, Andes virus and its close relatives in Argentina and Chile, and Laguna Negra virus in Paraguay. Each of these viruses is associated with a specific rodent of the subfamily Sigmodontinae, family Muridae. HCPS-associated viruses represent a monophyletic lineage (a group that shares a common ancestor) in the hantavirus phylogenetic (family) tree.
In most cases, a "new" hantavirus is easily recognized by its distinct protein sequences and distinct ecological niche. At the level of
nucleotide sequence, it is extremely unlikely to encounter two viruses of the same species that differ in nucleotide sequence by less than a
few percent except when they are closely linked to one another geographically. At a given geographic point, such as a case-patient's
household, anywhere from about 1-5 distinct SNV lineages may be present. For Sin Nombre viruses collected at two points across a
distance of 10 or more kilometers, it is usually easy to distinguish the prevailing viral genotypes.
We have been active in the use of molecular epidemiologic methods to distinguish among two or more potential sites of exposure- to distinguish, for example, workplace exposures from exposures at the home (ref, ref, ref). We compare the sequence of the virus from a patient with the viruses in circulation in rodents at his putative sites of exposure. These studies can be used as evidence to support specific models for exposure to hantavirus infection. Patients' risk activities are usually different at different sites of potential exposure. We are interested in continuing these investigations on a case-by-case basis with interested collaborators. The purpose of these studies is to better define the precise activities that lead to infection with hantaviruses. Of special interest to us are cases of HCPS that occur outside of the range of the deer mouse Peromyscus maniculatus; cases for which conventional epidemiologic investigations have failed to identify a single geographic site at which the exposure was likely to have occurred. This work has been supported for several years by the National Institutes of Health.
