Haemophilus somnus: Bovine Reproductive and Respiratory Disease.

Haemophilus somnus causes a variety of clinical problems in cattle including thrombotic meningoencephalitis, septicemia, arthritis, respiratory infections and reproductive failure (1-9). Encephalitic disease has been reliably reproduced (10) and host responses to whole organisms, or extracted antigens have been reported (I 1,12). Studies of reproductive and respiratory disease have been more limited. In field cases, H. somnus has been associated with abortion (2,3,5,6,8) infertility (3,5) and with the normal male or female reproductive tract (12,13,14). Abortion has been reproduced by inoculation of H. somnus into the middle uterine artery or by intra-amniotic inoculation but more natural routes have not resulted in abortion or well documented infertility. Although several studies have shown H. somnus to be associated with bovine respiratory disease (3,4,5), few have reproduced the disease. Even if all syndromes in the H. somnus complex are considered, little has been done on mechanisms of pathogenesis (I15,16,17,18), serological diagnosis (11) or subunit vaccines (12a). In order to gain a greater understanding of host parasite relationships in H. somnus pneumonia and abortion, and to develop improved methods of diagnosis and control, our research group has developed a multifaceted approach with several overlapping projects ongoing. As described below, we first studied the natural disease, then attempted to reproduce respiratory and reproductive disease in order to study pathogenesis, diagnosis and prophylaxis. Natural Disease In order to gain some insight into the relevance of H. somnus disease in the Northwestern United States, we reviewed cases submitted to the Washington Animal Disease diagnostic Laboratory (WADDL). From pneumonia cases in 1983 the WADDL bacteriology laboratory reported approximately equal numbers of cases due to Pasteurella haemolytica, P. multocida and H. somnus. It was not uncommon to isolate two of these three bacteria from the same pneumonic lung. From January I to September 30, 1983 the WADDL bacteriology laboratory reported nine cases of H. somnus induced abortion where the organism was isolated from the fetal tissues or stomach contents. Mixed infections with other pathogens were not characteristic of abortion in contrast to pneumonia. Haemophilus somnus was isolated from several cases of infertility also but it was difficult to interpret the etiological significance of these results, in light of recent reports of H. somnus colonization of the genital tract of normal bulls (12,13,14). Consequently we surveyed several herds for the presence of H. somnus on mucosal surfaces. This was done to confirm the presence of H. somnus in normal bulls as reported by others ( 12,13), to extend these studies to the female genital tract and to compare reproductive and respiratory colonization. Our data for preputial colonization agreed with data from other studies (12,13) showing that many normal bulls harbor this organism (Table I). Furthermore, our study showed that although females are less often colonized than bulls, the prevalence of 15% positive vaginal cultures indicates that normal heifers and cows often carry H. somnus asymptomatically. In both cases, positive nasal cultures were much less common than positive genital cultures. From these cultural studies of normal herds and observations from clinical cases as well as from published data (1-9,11-13), it can be concluded that H. somnus is both a pathogen and a commensal organism. Whether different strains cause disease or result in a commensal relationship is unknown. To answer this question it is necessary to develop experimental disease in the natural host. Since an experimental model had been reported only for encephalitis (10), we needed to develop models for respiratory and reproductive disease.