Rodent-borne infectious disease outbreaks after flooding disasters: Epidemiology, management, and prevention.

OBJECTIVE: To alert clinicians to the climatic conditions that can precipitate outbreaks of the rodent-borne infectious diseases most often associated with flooding disasters, leptospirosis (LS), and the Hantavirus-caused diseases, hemorrhagic fever with renal syndrome (HFRS) and Hantavirus pulmonary syndrome (HPS); to describe the epidemiology and presenting clinical manifestations and outcomes of these rodent-borne infectious diseases; and to recommend both prophylactic therapies and effective control and prevention strategies for rodent-borne infectious diseases. DESIGN: Internet search engines, including Google®, Google Scholar®, Pub Med, Medline, and Ovid, were queried with the key words as search terms to examine the latest scientific articles on rodent-borne infectious disease outbreaks in the United States and worldwide to describe the epidemiology and presenting clinical manifestations and outcomes of LS and Hantavirus outbreaks. SETTING: Not applicable. PARTICIPANTS: Not applicable. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURE: Rodent-borne infectious disease outbreaks following heavy rainfall and flooding disasters. RESULTS: Heavy rainfall encourages excessive wild grass seed production that supports increased outdoor rodent population densities; and flooding forces rodents from their burrows near water sources into the built environment and closer to humans. CONCLUSIONS: Healthcare providers should maintain high levels of suspicion for LS in patients developing febrile illnesses after contaminated freshwater exposures following heavy rainfall, flooding, and even freshwater recreational events; and for Hantavirus-caused infectious diseases in patients with hemorrhagic fevers that progress rapidly to respiratory or renal failure following rodent exposures.

A habitat-based model for the spread of hantavirus between reservoir and spillover species.

New habitat-based models for spread of hantavirus are developed which account for interspecies interaction. Existing habitat-based models do not consider interspecies pathogen transmission, a primary route for emergence of new infectious diseases and reservoirs in wildlife and man. The modeling of interspecies transmission has the potential to provide more accurate predictions of disease persistence and emergence dynamics. The new models are motivated by our recent work on hantavirus in rodent communities in Paraguay. Our Paraguayan data illustrate the spatial and temporal overlaps among rodent species, one of which is the reservoir species for Jabora virus and others which are spillover species. Disease transmission occurs when their habitats overlap. Two mathematical models, a system of ordinary differential equations (ODE) and a continuous-time Markov chain (CTMC) model, are developed for spread of hantavirus between a reservoir and a spillover species. Analysis of a special case of the ODE model provides an explicit expression for the basic reproduction number, R(0), such that if R(0)<1, then the pathogen does not persist in either population but if R(0)>1, pathogen outbreaks or persistence may occur. Numerical simulations of the CTMC model display sporadic disease incidence, a new behavior of our habitat-based model, not present in other models, but which is a prominent feature of the seroprevalence data from Paraguay. Environmental changes that result in greater habitat overlap result in more encounters among various species that may lead to pathogen outbreaks and pathogen establishment in a new host.

Experimental evaluation of rodent exclusion methods to reduce hantavirus transmission to residents in a Native American community in New Mexico.

We conducted a pilot study to evaluate the efficacy of rodent proofing continuously occupied homes as a method for lowering the risk for hantavirus pulmonary syndrome (HPS) among residents of a Native American community in northwestern New Mexico. Rodent proofing of dwellings was paired with culturally appropriate health education. Seventy homes were randomly assigned to treatment or control categories. Treatment homes were rodent-proofed by sealing openings around foundations, doors, roofs, and pipes and repairing screens and windows. Repairs to each dwelling were limited to $500 US. After repairs were completed, 15-20 snap traps were placed in each treatment and control home and checked approximately every 2 days for an average of 3-4 weeks. During 23,373 trap nights, one house mouse (Mus musculus) was captured in one treatment home, and 20 mice (16 deer mice, Peromyscus maniculatus, two Pinyon mice, Peromyscus truei, and two unidentified mice) were captured in five control homes (one house had 14 captures, two had two captures, and two had one capture). Trap success was 0.01% in treatment homes and 0.15% in controls. Intensity of infestation (mean number of mice captured per infested home) was 1 in treatment homes and 4 in controls. Observations of evidence of infestation (feces, nesting material, gnaw marks, or reports of infestation by occupant) per 100 days of observation were 1.2 in treatment homes and 3.1 in controls. Statistical power of the experiment was limited because it coincided with a period of low rodent abundance (August-November 2000). Nevertheless, these results suggest that inexpensive rodent proofing of occupied rural homes can decrease the frequency and intensity of rodent intrusion, thereby reducing the risk of HPS among rural residents in the southwestern United States.

Assessment of occupational risk for hantavirus infection in Arizona and New Mexico.

Differentiating occupational exposure from other potential domestic or recreational exposure(s) for Sin Nombre virus (SNV) infection is an epidemiologic challenge. Interviews on work-related activities were conducted, and serum specimens were obtained from 494 workers in Arizona and New Mexico. These workers may have been exposed to rodents and rodent excreta at work, but their primary occupation did not require rodent contact (National Park Service [n = 193]; Navajo Agricultural Product Industry [n = 65], utility companies [n = 169] and plumbing and heating contractors [n = 67]. Within each occupational group (farm workers [n = 57], laborers [n = 20], professionals [n = 70], repairers [n = 211], service industry workers [n = 83], and technicians [n = 53], the majority of workers reported working in areas that had rodent droppings (range, 75 to 95%); 70% of laborers and 64% of service industry workers reported handling rodents. More than 60% of workers in each group, except technicians, reported reopening and cleaning or working in closed spaces. Approximately 90% of laborers, repairers, and farm workers reported hand-plowing. Although the risk for occupationally related SNV infection appears to be low, workers frequently performed risk activities associated with hantavirus pulmonary syndrome (HPS). All workers were seronegative for SNV by enzyme-linked immunoassay or Western blot testing. These findings, the known occupational exposure of some HPS cases, and the high HPS case-fatality rate (52%) support the need for recommendations to reduce human contact with rodents in the workplace. Increased understanding of hantavirus transmission to humans will help focus future recommendations to minimize human exposures effectively.