Old Enemies, Still with Us after All These Years

Abstract

Although some previously common infections, such as Sendai virus and Mycoplasma pulmonis, have become rare in laboratory rodents in North American research facilities, others continue to plague researchers and those responsible for providing biomedical scientists with animals free of adventitious disease. Long-recognized agents that remain in research facilities in the 21st century include parvoviruses of rats and mice, mouse rotavirus, Theilers murine encephalomyelitis virus (TMEV), mouse hepatitis virus (MHV), and pinworms. The reasons for their persistence vary with the agent. The resilience of parvoviruses, for example, is due to their resistance to inactivation, their prolonged shedding, and difficulties with detection, especially in C57BL/6 mice. Rotavirus also has marked environmental resistance, but periodic reintroduction into facilities, possibly on bags of feed, bedding, or other supplies or equipment, also seems likely. TMEV is characterized by resistance to inactivation, periodic reintroduction, and relatively long shedding periods. Although MHV remains active in the environment at most a few days, currently prevalent strains are shed in massive quantities and likely transmitted by fomites. Pinworm infestations continue because of prolonged infections, inefficient diagnosis, and the survivability of eggs of some species in the environment. For all of these agents, increases in both interinstitutional shipping and the use of immunodeficient or genetically modified rodents of unknown immune status may contribute to the problem, as might incursions by wild or feral rodents. Elimination of these old enemies will require improved detection, strict adherence to protocols designed to limit the spread of infections, and comprehensive eradication programs.

Sero-Prevalence of Rodent Pathogens in India

“…Out of the six pathogens tested for mice, incidence of MHV was high in India. Being very susceptible to heat, detergents, desiccation and disinfectants, MHV would not be expected to sustain in the environment but its high prevalence may be due to its highly contagious nature [ 7 ], and the fact that it is shed in feces in large quantities for as long as four weeks after infection [ 34 ]. By contrast, the significant prevalence of parvoviral infections in rats can be attributed to their resistance to many of the common disinfectants, and stability in the environment [ 35 ] in addition to prolonged fecal shedding, leading to persistence of RPV in rat colonies [ 36 ].…”

Lurking in the Shadows: Emerging Rodent Infectious Diseases

“…Eradication involves standard approaches (e.g., depopulation, rederivation, neonatal transfer, antimicrobial therapy, stop breeding, test and cull) covered in detail elsewhere in this issue (Clifford and Watson 2008;Shek 2008). However, successful eradication is frequently where previously unrecognized (emerging) agents pose the most difficulty as they have somehow managed to survive in laboratory rodent colonies for decades without detection despite continual efforts to eliminate other infectious agents.…”

Biology and Diseases of Rats

“…In such colonies, reduced litter size, runted litters, and fetal and neonatal death may be observed. Serological surveys of rat colonies have indicated that rat parvoviruses, especially RPV (Liang et al, 2009;Livingston and Riley, 2003;Mahler and Kohl, 2009;McInnes et al, 2011;Pritchett-Corning et al, 2009;Schoondermark-van de Ven et al, 2006;Clifford and Watson, 2008) are among the most prevalent viruses of contemporary research rat colonies; however, clinical disease is rarely reported. The ability of RV to cross the placenta appears to depend on the virus strain, dose, and time of gestation.…”

“…Their continued prevalence (Liang et al, 2009;Livingston and Riley, 2003;McInnes et al, 2011, Pritchett-Corning et al, 2009, Schoondermark-van de Ven et al, 2006, Clifford and Watson, 2008, despite the dramatic progress in eliminating viral and bacterial pathogens, is due both to the persistence of the eggs in the environment and to the low degree of attention paid to these parasites. Their continued prevalence (Liang et al, 2009;Livingston and Riley, 2003;McInnes et al, 2011, Pritchett-Corning et al, 2009, Schoondermark-van de Ven et al, 2006, Clifford and Watson, 2008, despite the dramatic progress in eliminating viral and bacterial pathogens, is due both to the persistence of the eggs in the environment and to the low degree of attention paid to these parasites.…”