Attempted transmission of contagious equine metritis 1977 to other domestic animal species

Nonimmune binding of equine immunoglobulin by the causative organism of contagious equine metritis, Taylorella equigenitalis

This study identifies nonimmune binding of equine immunoglobulin by the causative organism of contagious equine metritis. Immunoglobulin binding to the bacterium was strongest for immunoglobulin G (IgG) and less for IgM; IgA was not bound. Binding of equine IgG was inhibited by human IgG, but not by IgG of domestic animals. Immunoglobulin binding by the bacterium appeared to be directed towards an epitope in the hinge region of the immunoglobulin molecule.

Contagious equine metritis: experimental infection in the donkey

Contagious equine metritis (CEM) was reproduced in 3 of 4 donkey mares with an Irish streptomycin-resistant strain of Haemophilus equigenitalis isolated from an experimental case of the disease in a pony mare. Although some variability in clinical response occurred, there was no evidence that semen enhanced the clinical severity of the infection. Variable amounts of vaginal discharge and associated inflammatory changes of the vagina and/or cervix, similar to those seen in the horse, were observed. All the affected donkeys made spontaneous clinical recoveries and so far as could be detected, subsequent persistence of H. equigenitalis in the genital tract was of limited duration. Recovery of the bacterium was not associated with oestrus and there was no evidence that it persisted in the clitoral area after it could no longer be cultured from the anterior genital tract. Cytological examination of smears of intra-uterine or cervical swabs was of diagnostic value only during the clinical phase of the infection. Serological responses demonstrated in 3 of the 4 donkey mares by the agglutination, complement-fixation and passive haemagglutination tests, were of low magnitude and short duration. The diagnostic value of the agglutination and complement-fixation tests was limited by the presence of low levels of non-specific reactivity and pronounced anti-complementary reactivity, respectively, in many of the donkey sera. The passive haemagglutination test proved superior for demonstrating elevation in antibody and for confirming infection. The overall results indicate that the donkey has the potential to act as a source of CEM infection and under certain circumstances, could have a role to play in the epidemiology of this disease.

Variable persistence of the contagious equine metritis organism in the genital tract of CBA/J, CBA/N, LAF1/J, BALB/c and congenitally thymus-deficient (nude) mice

Five inbred strains of mice, CBA/J, CBA/N, LAF1, BALB/c and congenitally thymus-deficient nude mice of BALB/c background, varied considerably in their susceptibility to the contagious equine metritis organism (CEMO). Whereas all the strains were virtually refractive to vaginal challenge, LAF1 and CBA/N mice were readily infected by intra-uterine inoculation. Based on infection rate and nature of the bacteriological response, CBA/N mice appeared the more susceptible of the 2 strains. Attempts to transmit CEMO to thymus-deficient nude mice were unsuccessful by both of these routes of challenge and by intraperitoneal inoculation, indicating that host resistance to the causal agent is independent of thymus-mediated immune phenomena. No clinical evidence of infection was observed in any of the experimentally infected mice. Although persistence of CEMO in the female reproductive tract varied widely, it could be isolated from some of the CBA/N mice for as long as 19 weeks after challenge by the intra-uterine route. The organism was cultured from the ovaries and/or oviducts of a high percentage of one group of CBA/N mice after 50 days, when it could no longer be recovered from the remainder of the genital tract. Limited attempts to achieve venereal transmission of CEMO between culture-positive female and companion male CBA/N mice were unsuccessful. The relative susceptibility of the CBA/N strain of mice to CEMO would suggest that host resistance to this infection is at least partly dependent on the presence of a fully functional B lymphocyte system. Further studies in this experimental model may elucidate some of the immunological mechanisms underlying development of resistance in the horse, more specifically as they relate to the occurrence of the carrier state in this disease.

Transmissibility of the contagious equine metritis organism for the cat

A group of SPF cats were moderately susceptible to the causal organism of contagious equine metritis (CEM) following intra-uterine or intrapreputial challenge with an Irish streptomycin resistant strain isolated from a clinically infected mare. Subclinical infections were established in only 50% of the cats, none of which became long-term carriers of the organism. Cytological examination of vaginal smears was of no diagnostic value in confirming infection in inapparently infected cats. Bacteriological responses after primary or secondary challenge with the CEM organism were essentially similar, with one exception, a female cat in which there was possible evidence of local immunity persisting after the primary infection. Efforts to reactivate shedding subsequent to the immediate post-challenge period were unsuccessful. Throughout the experimental period, the cats remained sero-negative to the complement-fixation test, and they failed to develop any significant increase in the levels of antibody activity as measured by the kinetics-based ELISA or KELA system. On day 89 after primary challenge, the cats were euthanized and various sites in the genitourinary tract and the internal iliac lymphatic glands subjected to bacteriological and pathological examination for evidence of CEM infection with negative results.

The findings of this study, although establishing the transmissibility of the CEM organism for the cat, demonstrate the limited value of this species as an experimental model system for the disease in the horse.