Risk of pathogen spillover to bighorn sheep from domestic sheep and goat flocks on private land

Pathology of Chronic Mycoplasma ovipneumoniae Carriers in a Declining Bighorn Sheep (Ovis canadensis) Population

Bighorn sheep (Ovis canadensis) across North America commonly experience population-limiting epizootics of respiratory disease. Although many cases of bighorn sheep pneumonia are polymicrobial, Mycoplasma ovipneumoniae is most frequently associated with all-age mortality events followed by years of low recruitment. Chronic carriage of M. ovipneumoniae by adult females serves as a source of exposure of naïve juveniles; relatively few ewes may be responsible for maintenance of infection within a herd. Test-and-remove strategies focused on removal of adult females with evidence of persistent or intermittent shedding (hereafter chronic carriers) may reduce prevalence and mitigate mortality. Postmortem confirmation of pneumonia in chronic carriers has been inadequately reported and the pathology has not been thoroughly characterized, limiting our understanding of important processes shaping the epidemiology of pneumonia in bighorn sheep. Here we document postmortem findings and characterize the lesions of seven ewes removed from a declining bighorn sheep population in Wyoming, USA, following at least two antemortem detections of M. ovipneumoniae within a 14-mo period. We confirmed that 6/7 (85.7%) had variable degrees of chronic pneumonia. Mycoplasma ovipneumoniae was detected in the lung of 4/7 (57.1%) animals postmortem. Four (57.1%) had paranasal sinus masses, all of which were classified as inflammatory, hyperplastic lesions. Pasteurella multocida was detected in all seven (100%) animals, while Trueperella pyogenes was detected in 5/7 (71.4%). Our findings indicate that not all chronic carriers have pneumonia, nor do all have detectable M. ovipneumoniae in the lung. Further, paranasal sinus masses are a common but inconsistent finding, and whether sinus lesions predispose to persistence or result from chronic carriage remains unclear. Our findings indicate that disease is variable in chronic M. ovipneumoniae carriers, underscoring the need for further efforts to characterize pathologic processes and underlying mechanisms in this system to inform management.

Development of a real-time PCR assay for detection and differentiation of Mycoplasma ovipneumoniae and a novel respiratory-associated Mycoplasma species in domestic sheep and goats

A novel respiratory-associated Mycoplasma species (M. sp. nov.) of unknown clinical significance was recently identified that causes false positive results with multiple published PCR methods reported to specifically detect Mycoplasma ovipneumonaie, a well-known respiratory pathogen in small ruminants. This necessitates our objective to develop a real-time PCR (qPCR) assay for improved specificity and sensitivity, and more rapid detection and differentiation of M. ovipneumoniae and the M. sp. nov. in domestic sheep (DS) and domestic goat (DG) samples, as compared to a conventional PCR and sequencing (cPCR-seq) assay. Primers and probes were designed based on available M. ovipneumoniae 16S rRNA gene sequences in the GenBank database, and partial 16S rRNA gene sequences provided by the United States Department of Agriculture, Agricultural Research Service (USDA-ARS) for M. ovipneumoniae and M. sp. nov. USDA-ARS provided DS (n = 153) and DG (n = 194) nasal swab nucleic acid that previously tested positive for either M. ovipneumoniae (n = 117) or M. sp. nov. (n = 138), or negative for both targets (n = 92) by cPCR-seq. A host 18S rRNA gene was included as an internal control to monitor for the failure of nucleic acid extraction and possible PCR inhibition. For samples positive by cPCR-seq, qPCR agreement was 88.0% (103/117; κ = 0.81) and 89.9% (124/138; κ = 0.84) for M. ovipneumoniae and M. sp. nov., respectively; 12 of 255 (4.7%) cPCR-seq positive samples were qPCR positive for both targets. Of samples negative by cPCR for both mycoplasmas, qPCR detected M. ovipneumoniae and M. sp. nov. in 6.5% (6/92) and 4.3% (4/92), respectively. Samples with discordant results between the cPCR and sequencing assay and the new qPCR were analyzed by target sequencing; successfully sequenced samples had identity matches that confirmed the qPCR result. The increased target specificity of this qPCR is predicted to increase testing accuracy as compared to other published assays.

Beware of dogs! Domestic animals as a threat for wildlife conservation in Alpine protected areas

Diseases are natural regulating factors of wildlife populations, but some pathogens may become an important threat in wildlife conservation, especially for endangered species. The presence of domestic animals may foster the spread of diseases in natural population, although their role in the dynamic of infections in wildlife is not clear. In this study, we investigated the presence and prevalence of a range of multi-host pathogens in wild species (red fox, Eurasian badger, beech marten, pine marten, stoat for a total of 89 carcasses analysed) and domestic animals (n = 52 shepherd and n = 25 companion dogs) living in a protected area of the Alps (the Gran Paradiso National Park) and discussed the role of domestic dogs as possible source of infection for wild species. Our results showed that domestic dogs are potential shedder of three important pathogens: Canine distemper virus, Toxoplasma sp. and Neospora caninum. In particular, shepherd dogs seem to represent a threat for wildlife as they are exposed to multiple pathogens because of free-roaming, scavenging lifestyles and close proximity to livestock. However, also companion dogs more subject to veterinary care may foster the spread of pathogens. Our results highlight the importance of regulating the access of domestic dogs to protected areas that aim at preserving biodiversity and enhancing the conservation of endangered species.

Genetic structure of Mycoplasma ovipneumoniae informs pathogen spillover dynamics between domestic and wild Caprinae in the western United States

Spillover diseases have significant consequences for human and animal health, as well as wildlife conservation. We examined spillover and transmission of the pneumonia-associated bacterium Mycoplasma ovipneumoniae in domestic sheep, domestic goats, bighorn sheep, and mountain goats across the western United States using 594 isolates, collected from 1984 to 2017. Our results indicate high genetic diversity of M. ovipneumoniae strains within domestic sheep, whereas only one or a few strains tend to circulate in most populations of bighorn sheep or mountain goats. These data suggest domestic sheep are a reservoir, while the few spillovers to bighorn sheep and mountain goats can persist for extended periods. Domestic goat strains form a distinct clade from those in domestic sheep, and strains from both clades are found in bighorn sheep. The genetic structure of domestic sheep strains could not be explained by geography, whereas some strains are spatially clustered and shared among proximate bighorn sheep populations, supporting pathogen establishment and spread following spillover. These data suggest that the ability to predict M. ovipneumoniae spillover into wildlife populations may remain a challenge given the high strain diversity in domestic sheep and need for more comprehensive pathogen surveillance.

Effect of dietary fiber levels on bacterial composition with age in the cecum of meat rabbits

This study investigated the influence of dietary fiber levels on the growth performance, digestion, metabolism, and cecal microbial community of rabbits with different diets at different age. The different levels of dietary natural detergent fiber (NDF) were formulated accordingly: 400(A), 350(B), 300(C), 250(D) g/kg original matter basis, respectively; the different ages were 52, 62, and 72 days. With NDF increasing, the average daily feed intake (ADFI) and feed conversion rate (FCR) were increased, whereas average daily gain (ADG) and mortality were decreased (p < 0.05). The stomach relative weight, stomach content relative weight, cecal relative weight, and cecal content weight increased with increasing NDF (p < 0.05). The NH3 -N concentration of cecum dropped when the dietary NDF increased (p < 0.05). The diversity of the total microbiota increased significantly in Diets B, C (p = 0.011), and reached the lowest in 52 days for all diet groups. The richness index was decreased significantly in Diet A, D (p < 0.05) and in 62 days (p < 0.001), respectively. The phylum Firmicutes was higher (p < 0.01) in rabbits fed Diets B, C than Diets A, D and Bacteroidetes was highest in Diets C, D, and Proteobacteria was the highest in Diet A (p < 0.001). Among the classified genera, there were 14 that had levels of abundance of more than 1% and were commonly shared by all samples. Ruminococcus spp. that produced volatile fatty acid (VFA) abundance was highest from Diets B, C at 52 and 62 days. It is interesting to note that Bifidobacterium from Diet C was the most abundant genus during the entire experimental period (p < 0.01). The data from Venn diagrams, principal component analysis (PCA), and heat map plots of the bacterial communities showed that there were more groups of shared microbiota with aging. The above results indicate the cecal microbiota controlled by the 350 g/kg NDF diet can prevent gastrointestinal distress and exhibit good production performance.

Risk factors and productivity losses associated with Mycoplasma ovipneumoniae infection in United States domestic sheep operations

Association of Mycoplasma ovipneumoniae with pneumonia in domestic small ruminants has been described in Europe, Asia, and New Zealand but has received less attention in the United States. In 2011, the US Department of Agriculture's National Animal Health Monitoring System detected M. ovipneumoniae shedding in 88% of 453 domestic sheep operations tested in 22 states that accounted for 85.5% of US ewe inventory in 2001. We evaluated factors associated with M. ovipneumoniae infection presence and prevalence, and we compared health, lamb production, and ewe losses in infected and uninfected operations. M. ovipneumoniae detection was more common in larger operations than in smaller operations. Both likelihood of detection (at the operation level) and within-operation prevalence were higher in operations with more open management practices than in operations with more closed management practices. M. ovipneumoniae-positive operations showed significantly lower lambing rates and lower rates of lamb survival to weaning after accounting for differences in operation size and management practice. While its effect on any single rate was not particularly large, in aggregate we estimated that M. ovipneumoniae presence was associated with an approximately 4.3% reduction in annual lamb production.

Respiratory pathogens and their association with population performance in Montana and Wyoming bighorn sheep populations

Respiratory disease caused by Mycoplasma ovipneumoniae and Pasteurellaceae poses a formidable challenge for bighorn sheep (Ovis canadensis) conservation. All-age epizootics can cause 10–90% mortality and are typically followed by multiple years of enzootic disease in lambs that hinders post-epizootic recovery of populations. The relative frequencies at which these epizootics are caused by the introduction of novel pathogens or expression of historic pathogens that have become resident in the populations is unknown. Our primary objectives were to determine how commonly the pathogens associated with respiratory disease are hosted by bighorn sheep populations and assess demographic characteristics of populations with respect to the presence of different pathogens. We sampled 22 bighorn sheep populations across Montana and Wyoming, USA for Mycoplasma ovipneumoniae and Pasteurellaceae and used data from management agencies to characterize the disease history and demographics of these populations. We tested for associations between lamb:ewe ratios and the presence of different respiratory pathogen species. All study populations hosted Pasteurellaceae and 17 (77%) hosted Mycoplasma ovipneumoniae. Average lamb:ewe ratios for individual populations where both Mycoplasma ovipneumoniae and Pasteurellaceae were detected ranged from 0.14 to 0.40. However, average lamb:ewe ratios were higher in populations where Mycoplasma ovipneumoniae was not detected (0.37, 95% CI: 0.27–0.51) than in populations where it was detected (0.25, 95% CI: 0.21–0.30). These findings suggest that respiratory pathogens are commonly hosted by bighorn sheep populations and often reduce recruitment rates; however ecological factors may interact with the pathogens to determine population-level effects. Elucidation of such factors could provide insights for management approaches that alleviate the effects of respiratory pathogens in bighorn sheep. Nevertheless, minimizing the introduction of novel pathogens from domestic sheep and goats remains imperative to bighorn sheep conservation.

Exposure of bighorn sheep to domestic goats colonized with Mycoplasma ovipneumoniae induces sub-lethal pneumonia

BACKGROUND

Bronchopneumonia is a population limiting disease of bighorn sheep (Ovis canadensis) that has been associated with contact with domestic Caprinae. The disease is polymicrobial but is initiated by Mycoplasma ovipneumoniae, which is commonly carried by both domestic sheep (O. aries) and goats (Capra aegagrus hircus). However, while previous bighorn sheep comingling studies with domestic sheep have resulted in nearly 100% pneumonia mortality, only sporadic occurrence of fatal pneumonia was reported from previous comingling studies with domestic goats. Here, we evaluated the ability of domestic goats of defined M. ovipneumoniae carriage status to induce pneumonia in comingled bighorn sheep.

METHODOLOGY/PRINCIPAL FINDINGS

In experiment 1, three bighorn sheep naïve to M. ovipneumoniae developed non-fatal respiratory disease (coughing, nasal discharge) following comingling with three naturally M. ovipneumoniae-colonized domestic goats. Gross and histological lesions of pneumonia, limited to small areas on the ventral and lateral edges of the anterior and middle lung lobes, were observed at necropsies conducted at the end of the experiment. A control group of three bighorn sheep from the same source housed in isolation during experiment 1 remained free of observed respiratory disease. In experiment 2, three bighorn sheep remained free of observed respiratory disease while comingled with three M. ovipneumoniae-free domestic goats. In experiment 3, introduction of a domestic goat-origin strain of M. ovipneumoniae to the same comingled goats and bighorn sheep used in experiment 2 resulted in clinical signs of respiratory disease (coughing, nasal discharge) in both host species. At the end of experiment 3, gross and histological evidence of pneumonia similar to that observed in experiment 1 bighorn sheep was observed in both affected bighorn sheep and domestic goats.

CONCLUSIONS/SIGNIFICANCE

M. ovipneumoniae strains carried by domestic goats were transmitted to comingled bighorn sheep, triggering development of pneumonia. However, the severity of the disease was markedly milder than that seen in similar experiments with domestic sheep strains of the bacterium.

Potential disease agents in domestic goats and relevance to bighorn sheep (Ovis canadensis) management

Domestic goats are raised for meat, milk and hair production, in herds for rangeland weed control, and as pack animals. Domestic sheep, goats and wild bighorn sheep are all susceptible to a multifactorial pneumonia. We sampled 43 herd goats from 7 herds and 48 pack goats from 11 herds for viral and bacterial serology, parasitology, and Pasteurellaceae microbiology. The goats in this study were in generally good health, although most goats did harbor various pathogens and parasites including several bacteria, specifically Pasteurellaceae, which have been associated with pneumonia in free-ranging bighorn sheep. It is not known if domestic goats can transmit the Pasteurellaceae or other pathogens found in this study readily to wild bighorn sheep. However, due the possibility of transmission, domestic goats in areas in or near bighorn sheep habitat should be managed to minimize the risk of spreading disease agents to bighorn sheep.