Dual captures of Colorado rodents: implications for transmission of hantaviruses

Following the Yellow Brick Road

Charles Calisher was fascinated by microorganisms from the time he was in high school. He attended Stuyvesant High School in New York City, Philadelphia College of Pharmacy and Science (now University of the Sciences) (BS), then University of Notre Dame in South Bend, Indiana (MS), and finally Georgetown University, in Washington, DC (PhD), the latter while employed at a commercial biological house. He was hired by the US Communicable Disease Center (now the Centers for Disease Control and Prevention) in Atlanta, Georgia, was transferred to its Fort Collins laboratories in 1973, and retired from there in 1992. After traveling the world a bit, Calisher joined the faculty of Colorado State University in 1993, then semiretired as professor emeritus in 2010. During all those years, he developed from a would-be virologist to an arbovirologist-epidemiologist, identifying scores of newly recognized viruses from throughout the world and helping to investigate disease outbreaks and epidemics. His interests (always primarily arboviruses but now also rodent-borne viruses and bat-borne viruses) continue to expand, and he continues to be involved in various aspects of virology and to assist and annoy journal editors and others in regard to viral taxonomy.

Alphacoronaviruses in New World bats: prevalence, persistence, phylogeny, and potential for interaction with humans

Bats are reservoirs for many different coronaviruses (CoVs) as well as many other important zoonotic viruses. We sampled feces and/or anal swabs of 1,044 insectivorous bats of 2 families and 17 species from 21 different locations within Colorado from 2007 to 2009. We detected alphacoronavirus RNA in bats of 4 species: big brown bats (Eptesicus fuscus), 10% prevalence; long-legged bats (Myotis volans), 8% prevalence; little brown bats (Myotis lucifugus), 3% prevalence; and western long-eared bats (Myotis evotis), 2% prevalence. Overall, juvenile bats were twice as likely to be positive for CoV RNA as adult bats. At two of the rural sampling sites, CoV RNAs were detected in big brown and long-legged bats during the three sequential summers of this study. CoV RNA was detected in big brown bats in all five of the urban maternity roosts sampled throughout each of the periods tested. Individually tagged big brown bats that were positive for CoV RNA and later sampled again all became CoV RNA negative. Nucleotide sequences in the RdRp gene fell into 3 main clusters, all distinct from those of Old World bats. Similar nucleotide sequences were found in amplicons from gene 1b and the spike gene in both a big-brown and a long-legged bat, indicating that a CoV may be capable of infecting bats of different genera. These data suggest that ongoing evolution of CoVs in bats creates the possibility of a continued threat for emergence into hosts of other species. Alphacoronavirus RNA was detected at a high prevalence in big brown bats in roosts in close proximity to human habitations (10%) and known to have direct contact with people (19%), suggesting that significant potential opportunities exist for cross-species transmission of these viruses. Further CoV surveillance studies in bats throughout the Americas are warranted.

Alphacoronaviruses in New World bats: prevalence, persistence, phylogeny, and potential for interaction with humans

Bats are reservoirs for many different coronaviruses (CoVs) as well as many other important zoonotic viruses. We sampled feces and/or anal swabs of 1,044 insectivorous bats of 2 families and 17 species from 21 different locations within Colorado from 2007 to 2009. We detected alphacoronavirus RNA in bats of 4 species: big brown bats (Eptesicus fuscus), 10% prevalence; long-legged bats (Myotis volans), 8% prevalence; little brown bats (Myotis lucifugus), 3% prevalence; and western long-eared bats (Myotis evotis), 2% prevalence. Overall, juvenile bats were twice as likely to be positive for CoV RNA as adult bats. At two of the rural sampling sites, CoV RNAs were detected in big brown and long-legged bats during the three sequential summers of this study. CoV RNA was detected in big brown bats in all five of the urban maternity roosts sampled throughout each of the periods tested. Individually tagged big brown bats that were positive for CoV RNA and later sampled again all became CoV RNA negative. Nucleotide sequences in the RdRp gene fell into 3 main clusters, all distinct from those of Old World bats. Similar nucleotide sequences were found in amplicons from gene 1b and the spike gene in both a big-brown and a long-legged bat, indicating that a CoV may be capable of infecting bats of different genera. These data suggest that ongoing evolution of CoVs in bats creates the possibility of a continued threat for emergence into hosts of other species. Alphacoronavirus RNA was detected at a high prevalence in big brown bats in roosts in close proximity to human habitations (10%) and known to have direct contact with people (19%), suggesting that significant potential opportunities exist for cross-species transmission of these viruses. Further CoV surveillance studies in bats throughout the Americas are warranted.

Emergence and persistence of hantaviruses

Hantaviral diseases have been recognized for hundreds of years but, until 1976, they had not been associated with an infectious agent. When Lee and colleagues isolated what is now known as Hantaan virus, the techniques they introduced allowed further investigations into the etiology of the classical hantavirus disease, hemorrhagic fever with renal syndrome (HFRS), now known to be caused by any of multiple hantaviruses. The discovery of hantavirus pulmonary syndrome (HPS) in the New World, and that it also can be caused by any of multiple hantaviruses (family Bunyaviridae, genus Hantavirus), has opened an entire field of epidemiologic, virologic, molecular, behavioral, and ecologic studies of these viruses. There appears to be a single hantavirus-single rodent host association, such that understanding the idiosyncrasies of each rodent host species and the ecologic variables that affect them are recognized as critical if we are to reduce human risk for infection. This chapter summarizes what is known about hantaviruses with regard to history of these viruses, their taxonomy, recognized geographical distribution, ecologic factors impacting their maintenance and spread of hantaviruses, effect of rodent behavior on hantavirus transmission, influence of host factors on susceptibility to and transmission of hantaviruses, and transmission of hantaviruses from rodents to humans. In addition, we summarize all these complexities and provide suggestions for future research directions.

Infectious disease modeling and the dynamics of transmission

The dynamics of any infectious disease are heavily dependent on the rate of transmission from infectious to susceptible hosts. In many disease models, this rate is captured in a single compound parameter, the probability of transmission P. However, closer examination reveals how beta can be further decomposed into a number of biologically relevant variables, including contact rates among individuals and the probability that contact events actually result in disease transmission. We start by introducing some of the basic concepts underlying the different approaches to modeling disease transmission and by laying out why a more detailed understanding of the variables involved is usually desirable. We then describe how parameter estimates of these variables can be derived from empirical data, drawing primarily from the existing literature on human diseases. Finally, we discuss how these concepts and approaches may be applied to the study of pathogen transmission in wildlife diseases. In particular, we highlight recent technical innovations that could help to overcome some the logistical challenges commonly associated with empirical disease research in wild populations.