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Mycoplasma pulmonis genital disease: effect of rat strain on pregnancy outcome
L Reyes1, D A Steiner, J Hutchison
1Department of Pathobiology, College of Veterinary Medicine, University of Florida, Gainesville 32611-0880, USA.
Background And Purpose:
Mycoplasma pulmonis is a natural pathogen of the respiratory and genital tracts of rats. Differential susceptibility and severity of the respiratory form of the disease, known as murine respiratory mycoplasmosis (MRM), exist between rat strains. We now report that specific rat strains vary in susceptibility to genital tract infection and pregnancy outcome.
Methods:
Specific-pathogen-free (SPF) female F344, LEW, Wistar (WIS) and Sprague Dawley (SD) rats were intravaginally inoculated with 3 x 10(7) colony-forming units (CFU) of M. pulmonis strain X1048 or sterile diluent, and allowed to breed at 10 days after inoculation. Pregnant dams and pups were necropsied within 24 hours of parturition. At necropsy, culture for M. pulmonis was performed on dam and pups, and adverse effects on pregnancy outcome were assessed by determination of the incidence of infertility, fetal resorption, stillbirths, changes in litter size, and pup birth weight. Blood from dams was collected prior to inoculation and at time of necropsy for measurement of IgM and IgG antibodies to M. pulmonis.
Results:
At time of necropsy, WIS (50%) and SD (60%) dams had a higher frequency of M. pulmonis culture positivity in the genital tract than did LEW (22.2%) and F344 (17.6%) dams. Dams that were still infected with M. pulmonis at time of necropsy had various complications. The SD rats had the greatest degree of adverse effects on pregnancy outcome, which were: infertility, decreased litter size (P < or = 0.01), decreased pup birth weight (P < or = 0.01), increased frequency of resorptions, stillbirths (P < or = 0.05), and the highest rate of pup pulmonary infection (23.1%) (P < or = 0.001). Despite a 50% colonization rate, WIS dams were the least adversely affected. The WIS pups born from M. pulmonis. infected dams had slight decrease in birth weight, and only 6% had pulmonary infections. The LEW infected dams developed infertility and lower numbers of liveborn pups without evidence of vertical transmission. The F344 infected dams had lower numbers of liveborn pups that were smaller than their control counterparts, and none had pulmonary infections. None of the animals had detectable IgM and IgG antibodies to M. pulmonis before inoculation. At time of necropsy, all animals inoculated with M. pulmonis developed significantly (P < or = 0.001) higher amounts of M. pulmonis IgG and IgM antibodies, with SD rats developing the highest amounts (P < or = 0.005).
Conclusions:
Both F344 and LEW rats are more resistant to vaginal inoculation with M. pulmonis than are WIS and SD rats. However, only SD dams suffered severe adverse effects on pregnancy outcome. The SD dams also had the greatest IgM and IgG antibody response to M. pulmonis. Our studies clearly indicate differences among rat strains in their susceptibility to vaginal inoculation with M. pulmonis and in secondary complications associated with infection. This system may be a useful model for determining host-specific factors that influence the outcome of natural mycoplasmal infections of the genital tract.
Insights
Different rat strains show varying susceptibility to Mycoplasma pulmonis genital tract infection, with Sprague Dawley rats experiencing the most severe pregnancy complications. This highlights strain-specific host factors influencing mycoplasmal infection outcomes.
Area of Science:
- Veterinary Pathology
- Infectious Diseases
- Reproductive Biology
Background:
- Mycoplasma pulmonis is a common pathogen affecting rat respiratory and genital tracts.
- Rat strains exhibit differential susceptibility to Mycoplasma pulmonis, leading to varied disease severity.
- Genital tract infection and its impact on pregnancy outcomes in different rat strains are not well-characterized.
Purpose of the Study:
- To investigate the susceptibility of specific rat strains (F344, LEW, Wistar, Sprague Dawley) to vaginal Mycoplasma pulmonis inoculation.
- To assess the effects of M. pulmonis genital tract infection on pregnancy outcomes, including infertility, fetal resorption, stillbirths, litter size, and pup birth weight.
- To evaluate the host immune response, specifically IgM and IgG antibody production, to M. pulmonis infection in different rat strains.
Main Methods:
- Specific-pathogen-free female rats of four strains were intravaginally inoculated with M. pulmonis or a control diluent.
- Inoculated rats were bred, and pregnant dams and pups were necropsied post-parturition.
- Genital tract cultures for M. pulmonis, assessment of pregnancy complications, and measurement of serum IgM and IgG antibodies were performed.
Main Results:
- Wistar and Sprague Dawley rats showed higher genital tract M. pulmonis colonization rates compared to LEW and F344 rats.
- Sprague Dawley dams experienced the most severe adverse pregnancy outcomes, including infertility, reduced litter size, lower pup birth weight, increased resorptions/stillbirths, and high pup pulmonary infection rates.
- LEW and F344 dams had fewer liveborn pups, with F344 pups being smaller; Wistar dams showed milder effects despite high colonization.
- All inoculated rats developed significant M. pulmonis-specific IgM and IgG antibodies, with Sprague Dawley rats exhibiting the highest levels.
Conclusions:
- F344 and LEW rats are more resistant to vaginal M. pulmonis inoculation than Wistar and Sprague Dawley rats.
- Sprague Dawley dams are highly susceptible to M. pulmonis genital infection, leading to severe adverse pregnancy outcomes and a strong antibody response.
- Rat strain differences in susceptibility and pregnancy complications underscore the importance of host-specific factors in natural mycoplasmal genital infections, suggesting a useful model for further research.
