Urban Biomes – An Ecological Niche For Potential Hantavirus Vectors
by Stewart Mitchell, PhD

Keywords: hantavirus, Sin Nombre virus, zoonotic disease vectors.

With the constant expansion of the anthrosphere (those habitats occupied by humans), biological and ecological diversity are severely adversely impacted. Ecological integrity is threatened when the urban developmental process refuses to subscribe to the earth wisdom view. The juxtaposition of interspecific competition from non-ecologically based land-use planning lends itself to parasitism of human living quarters. Increasingly, urban biomes create a niche for zoonotic disease vectors through commensal exposure.

One emergent zoonotic disease inoculant that is derivative of commensal exposure is hantavirus. Hantavirus defined its profile within the public health arena when 131 people were found to be infected – resulting in 65 deaths in the southwestern United States, between 1993 and 1996.

Numerous hantaviruses have been identified in North America. Hantaviruses are 3-segmented RNA viruses with spherical to oval particles, 95 – 110 nm per diameter. In excess of 25 antigenically distinguishable species exist, each in association with a group or singular rodent species.

Sin Nombre virus is the inoculum causal to the 1993 epidemic absolute to Native Americans in the Four Corners area of New Mexico and Arizona. Geographical cluster cases have subsequently bloomed in other Western and Eastern states, as well as Canada.

Sin Nombre virus inoculum onsets to Hantavirus Pulmonary Syndrome (HPS). Presentation by morbidity is fever, myalgias, gastro-intestinal discomfort, ultimate acute respiratory distress, and hypotension. Progression is rapid toward respiratory failure and shock. The mortality rate is 40 – 50%. Symptoms develop between one and five weeks from exposure. The incubation period is incompletely defined.

Diagnosis is demonstrative of IgM antibodies using ELISA, Western Blot, or Strip Immunoblot techniques. Additional diagnostic protocols include PCR and immunohistochemical analysis of biopsy tissues.

Early presentation and appropriate diagnosis proceeding to emergeny medical attention improves the prognosis of recovery. Intensive care patients are intubated with oxygen therapy. Full convalescence may occur within a few weeks if the infection is detected early in its cycle (assuming no complications from immunosuppression). Restoration of normal lung function generally occurs; however, chronic pulmonary function abnormalities may persist.

The persistent reservoir and transvector of Sin Nombre virus is the paracleptoparasitic deer mouse, Peromyscus maniculatus. Additionally, the white-footed mouse, Peromyscus leucopus, wood rat and pack rat, genus Noetoma, cotton rat, Sigmodon hispidus, and the rice rat Oryzomys palustris, have periodically been found to vector the disease.

The urbanization of natural biomes becomes an ecotone between anthropogenic processes and population ecology which redefines the fundamental niche of species and to some degree, their trophic level. Urbanization, no matter how pragmatic, benefits the r-strategist, specifically rodents.

Rodents benefit from the shelter, food, and water that are unwittingly provided by human beings. This amutualistic relationship sets into motion a competition for our survival or at the very least, our well being. Through the activities of this presumed nefarious zoological order, we find ourselves potentially exposed to zoonotically transmissible diseases like hantavirus.

The Sin Nombre virus is vectored (i.e. transmitted) primarily by deer mice. The virion is a symbiant within the mice. The deer mouse genus belongs to the family Cricetidae (meaning "hamster-like"). The common name originates from the perceived resemblance of the rodent's fur to that of the white-tailed deer, Odocoileus virginianus.

The population distribution of the deer mouse covers much of North America. Population densities are more sporadic in the Eastern and Southeastern United States. The population dynamic of the deer mouse intersects urban biomes in transitionally developing regions, specifically, structures within semi-rural and newly developed areas. Deer mice commonly invade human structures during times of environmental stress, searching for food or water in times of scarcity. The 1993 Sin Nombre event is attributed in part to the severe drought that proceeded the outbreak.