Infectious keratoconjunctivitis in wild Caprinae: merging field observations and molecular analyses sheds light on factors shaping outbreak dynamics

Infectious keratoconjunctivitis in European bison (Bison bonasus) in Poland: risk factors, epidemiology and anatomopathological changes with analysis of potential role of Thelazia nematodes in the disease development

BACKGROUND

Infectious keratoconjunctivitis (IKC) is a common ocular disease of ruminants worldwide. Recently, an outbreak of infectious keratoconjunctivitis was observed in the European bison in Poland. Hundreds of animals show conjunctival congestion, corneal opacity, and ulceration, leading to total blindness. The present study aimed to examine the ocular changes of European bison and patterns of the disease occurrence with special emphasis on the role of Thelazia nematodes in the development of IKC.

RESULTS

The eyes of 131 European bison, showing ocular signs and clinically healthy, were collected in Poland in 2021 - 2022 and subjected to parasitological and histopathological examination. Histopathology showed varying lesions, including corneal erosions or ulcers, diffuse purulent infiltrates to lymphocytic infiltration in the cornea, and lymphocytic or mixed conjunctivitis with CALT stimulation. The severity of ocular changes was higher in European bison from mountain areas and during the winter season. Two species of Thelazia nematodes - T. skrjabini and T. gulosa have been isolated from eyes. Prevalence of infection reached over 66.4%, and the infection intensity ranged from 1 to 16 nematodes per individual. Although nematodes of the genus Thelazia were prevalent in European bison, their occurrence did not correspond with the severity of ocular changes.

CONCLUSIONS

The results of our studies allowed to identify patterns related to the first outbreak of infectious keratoconjunctivitis in European bison. Living in mountain areas and winter season were the most predisposing factors for the development of ocular changes. Despite the high prevalence of Thelazia nematodes in the present study, their role in forming ocular lesions was not confirmed.

Wildlife-Livestock Host Community Maintains Simultaneous Epidemiologic Cycles of Mycoplasma conjunctivae in a Mountain Ecosystem

Infectious keratoconjunctivitis (IKC) is an eye disease caused by Mycoplasma conjunctivae that affects domestic and wild caprines, including Iberian ibex (Capra pyrenaica), a medium-sized mountain ungulate. However, its role in IKC dynamics in multi-host communities has been poorly studied. This study assessed M. conjunctivae in Iberian ibex and seasonally sympatric domestic small ruminants in the Natural Space of Sierra Nevada (NSSN), a mountain habitat in southern Spain. From 2015 to 2017, eye swabs were collected from 147 ibexes (46 subadults, 101 adults) and 169 adult domestic small ruminants (101 sheep, 68 goats). Mycoplasma conjunctivae was investigated through real-time qPCR and statistically assessed according to species, sex, age category, year, period, and area. The lppS gene of M. conjunctivae was sequenced and phylogenetically analysed. Mycoplasma conjunctivae was endemic and asymptomatic in the host community of the NSSN. Three genetic clusters were shared by ibex and livestock, and one was identified only in sheep, although each host species could maintain the infection independently. Naïve subadults maintained endemic infection in Iberian ibex, with an epizootic outbreak in 2017 when the infection spread to adults. Wild ungulates are epidemiologically key in maintaining and spreading IKC and other shared diseases among spatially segregated livestock flocks.

Galleria mellonella Invertebrate Model Mirrors the Pathogenic Potential of Mycoplasma alligatoris within the Natural Host

Most mycoplasmal infections result in chronic, clinically silent disease. In direct contrast, Mycoplasma alligatoris elicits a fulminant, multisystem disease in the natural host, Alligator mississippiensis (American alligator). The goals of the study were to better understand the disease in the natural host and to determine if the invertebrate model G. mellonella could serve as a surrogate alternate host. The survival of alligators infected intratracheally was dose dependent (p=0.0003), ranging from no mortality (102 CFU) to 100% mortality (108 CFU), with 60% mortality at the 104 and 105 CFU infectious dose. Microbial load in blood, joints, and brain was dose dependent, regardless of whether alligators were infected intratracheally or intravenously (p  < 0.002). Weight loss was similarly impacted (p  < 0.001). Experimental infection of the invertebrate Galleria mellonella mirrored the result in the natural host. In a dose response infection study, both larval survival curves and successful pupation curves were significantly different (p ≤ 0.0001) and dose dependent. Infected insects did not emerge as moths (p  < 0.0001). Here, we describe the first study investigating G. mellonella as a surrogate model to assess the pathogenic potential of M. alligatoris. G. mellonella survival was dose dependent and impacted life stage outcome.

Mycoplasma agalactiae ST35: a new sequence type with a minimal accessory genome primarily affecting goats

Background

Mycoplasma agalactiae, causing agent of contagious agalactia, infects domestic small ruminants such as sheep and goats but also wild Caprinae. M. agalactiae is highly contagious and transmitted through oral, respiratory, and mammary routes spreading rapidly in an infected herd.

Results

In an outbreak of contagious agalactia in a mixed herd of sheep and goats, 80% of the goats were affected displaying swollen udders and loss of milk production but no other symptom such as kerato-conjunctivitis, arthritis or pulmonary distress commonly associated to contagious agalactia. Surprisingly, none of the sheep grazing on a common pasture and belonging to the same farm as the goats were affected. Whole genome sequencing and analysis of M. agalactiae strain GrTh01 isolated from the outbreak, revealed a previously unknown sequence type, ST35, and a particularly small, genome size of 841′635 bp when compared to others available in public databases. Overall, GrTh01 displayed a reduced accessory genome, with repertoires of gene families encoding variable surface proteins involved in host-adhesion and variable antigenicity being scaled down. GrTh01 was also deprived of Integrative Conjugative Element or prophage, and had a single IS element, suggesting that GrTh01 has a limited capacity to adapt and evolve.

Conclusions

The lack of most of the variable antigens and the Integrative Conjugative Element, both major virulence- and host specificity factors of a M. agalactiae strain isolated from an outbreak affecting particularly goats, indicates the implication of these factors in host specificity. Whole genome sequencing and full assembly of bacterial pathogens provides a most valuable tool for epidemiological and virulence studies of M. agalactiae without experimental infections.

Identifying maintenance hosts for infection with Dichelobacter nodosus in free-ranging wild ruminants in Switzerland: A prevalence study

Footrot is a worldwide economically important, painful, contagious bacterial foot disease of domestic and wild ungulates caused by Dichelobacter nodosus. Benign and virulent strains have been identified in sheep presenting with mild and severe lesions, respectively. However, in Alpine ibex (Capra ibex ibex), both strains have been associated with severe lesions. Because the disease is widespread throughout sheep flocks in Switzerland, a nationwide footrot control program for sheep focusing on virulent strains shall soon be implemented. The aim of this cross-sectional study was to estimate the nationwide prevalence of both strain groups of D. nodosus in four wild indigenous ruminant species and to identify potential susceptible wildlife maintenance hosts that could be a reinfection source for domestic sheep. During two years (2017–2018), interdigital swabs of 1,821 wild indigenous ruminant species (Alpine ibex, Alpine chamois (Rupicapra rupicapra), roe deer (Capreolus capreolus), red deer (Cervus elaphus)) were analysed by Real-Time PCR. Furthermore, observed interspecies interactions were documented for each sample. Overall, we report a low prevalence of D. nodosus in all four indigenous wild ruminants, for both benign (1.97%, N = 36, of which 31 red deer) and virulent (0.05%, N = 1 ibex) strains. Footrot lesions were documented in one ibex with virulent strains, and in one ibex with benign strains. Interspecific interactions involving domestic livestock occurred mainly with cattle and sheep. In conclusion, the data suggest that wild ungulates are likely irrelevant for the maintenance and spread of D. nodosus. Furthermore, we add evidence that both D. nodosus strain types can be associated with severe disease in Alpine ibex. These data are crucial for the upcoming nationwide control program and reveal that wild ruminants should not be considered as a threat to footrot control in sheep in this context.

Mycoplasma conjunctivae-Associated Keratoconjunctivitis in Norwegian Muskox (Ovibos moschatus)

In late summer 2014, an outbreak of ocular disease occurred in the Norwegian muskox (Ovibos moschatus) population. Animals showed rings of pus around their eyes and one euthanized animal was diagnosed with acute keratoconjunctivitis. The DNA sequence analysis of eye-swab samples from this animal revealed a high abundance of Mycoplasma conjunctivae.

Sanitary Emergencies at the Wild/Domestic Caprines Interface in Europe

Simple Summary

Even if it is an important achievement from a biodiversity conservation perspective, the documented increase in abundance of the four native European wild Caprinae (Rupicapra rupicapra, R. pyrenaica, Capra ibex, C. pyrenaica) can also be a matter of concern, since tighter and more frequent contact with sympatric livestock implies a greater risk of transmission of emerging and re-emerging pathogens. This article reviews the main transmissible diseases that, in a European scenario, are of greater significance from a conservation perspective. Epidemics causing major demographic downturns in wild Caprinae populations during recent decades were often triggered by pathogens transmitted at the livestock/wildlife interface.

Abstract

Population density and distribution of the four native European wild Caprines (Rupicapra rupicapra, Rupicapra pyrenaica, Capra ibex, Capra pyrenaica) have increased in recent decades. The improved conservation status of this valuable wildlife, while a welcome event in general terms, is at the same time a matter of concern since, intuitively, frequent and tighter contacts with sympatric livestock imply a greater risk of cross-transmission of emerging and re-emerging pathogens, and offer unexpected opportunities for pathogens to spread, persist and evolve. This article recalls the transmissible diseases that are perceived in Europe to be of major significance from a conservation perspective, namely brucellosis (BRC) by Brucella melitensis, infectious kerato-conjunctivitis (IKC) by Mycoplasma conjunctivae, pestivirosis (PV) by the border disease virus strain 4 and mange by Sarcoptes scabiei. Special emphasis has been put on the epidemiological role played by small domestic ruminants, and on key knowledge needed to implement evidence-based prevention and control strategies. Remarkably, scientific evidence demonstrates that major demographic downturns in affected wild Caprinae populations in recent decades have often been triggered by pathogens cross-transmitted at the livestock/wildlife interface.

Screening of wild ruminants from the Kaunertal and other alpine regions of Tyrol (Austria) for vector-borne pathogens

Knowledge about vector-borne pathogens important for human and veterinary medicine in wild ruminants in Tyrol (Austria) is scarce. Blood samples from Alpine ibex (Capra ibex; n = 44), Alpine chamois (Rupicapra rupicapra; n = 21), roe deer (Capreolus capreolus; n = 18) and red deer (Cervus elaphus; n = 6) were collected over a period of 4 years (2015–2018) in four regions in North Tyrol, with a primary focus on the Kaunertal. Blood spots on filter paper were tested for the presence of DNA of vector-borne pathogens (Anaplasmataceae, Piroplasmida, Rickettsia and filarioid helminths). Anaplasma phagocytophilum and Babesia capreoli were detected in two of 89 (2.3%) blood samples. Rickettsia spp., Theileria spp. and filarioid helminths were not documented. One Alpine chamois was positive for A. phagocytophilum and B. capreoli. Moreover, an ibex from the Kaunertal region was positive for A. phagocytophilum. While the ibex was a kid less than 1 year old, the chamois was an adult individual. Further research is recommended to evaluate effects of climate change on infection rates of North Tyrolean wild ruminants by these pathogens and the distribution of their vectors.

Mycoplasma conjunctivae in insect vectors and anatomic locations related to transmission and persistence

Mycoplasma conjunctivae is an obligate microparasite that causes Infectious Keratoconjunctivitis (IKC) in Caprinae species. IKC is a long-recognised disease, but little attention has been paid to the mechanisms of transmission of the mycoplasma and its occurrence in locations other than the eyes. In this study, the presence of M. conjunctivae is assessed in the eyes, external ear canals (EEC), nasal cavity, and vagina of host species as well as in potential vectors, which may be involved in the transmission and persistence of infection within the host. M. conjunctivae was detected by qPCR in 7.2 % (CI 95% 4.7-11.0) of the ear swabs and 9.5 % (CI 95% 6.4-13.9) of the nasal swabs from Pyrenean chamois, Iberian ibex, domestic sheep and mouflon without statistical differences between species. Mycoplasma detection in nasal swabs was mostly associated with ocular infection (95.6%), but this was not the case for EEC (52.6%). Among the eye-positive ruminants, 27.3% were positive in ear swabs and 64.7% in nasal swabs, and the threshold cycle values of the qPCR were correlated only between eye and nasal swabs (p < 0.01; r₂ = 0.56). M. conjunctivae was detected in 1.7% - 7.1 % of Musca spp. captured during an IKC outbreak in Iberian ibex and in one out of three endemic sheep flocks. The results indicate that the transmission of M. conjunctivae may occur by direct contact with eye or nasal secretions and/or indirectly through flies. The M. conjunctivae DNA detection in EEC suggests that it can colonise the auditory tract, but the significance for its persistence within the host should be further assessed.

Heterozygosity-fitness correlation at the major histocompatibility complex despite low variation in Alpine ibex (Capra ibex)

Crucial for the long-term survival of wild populations is their ability to fight diseases. Disease outbreaks can lead to severe population size reductions, which makes endangered and reintroduced species especially vulnerable. In vertebrates, the major histocompatibility complex (MHC) plays an important role in determining the immune response. Species that went through severe bottlenecks often show very low levels of genetic diversity at the MHC. Due to the known link between the MHC and immune response, such species are expected to be at particular risk in case of disease outbreaks. However, so far, only few studies have shown that low MHC diversity is correlated with increased disease susceptibility in species after severe bottlenecks. We investigated genetic variation at the MHC and its correlations with disease resistance and other fitness-related traits in Alpine ibex (Capra ibex), a wild goat species that underwent a strong bottleneck in the last century and that is known to have extremely low genetic variability, both genome-wide and at the MHC. We studied MHC variation in male ibex of Gran Paradiso National Park, the population used as a source for all postbottleneck reintroductions. We found that individual MHC heterozygosity (based on six microsatellites) was not correlated with genome-wide neutral heterozygosity. MHC heterozygosity, but not genome-wide heterozygosity, was positively correlated with resistance to infectious keratoconjunctivitis and with body mass. Our results show that genetic variation at the MHC plays an important role in disease resistance and, hence, should be taken into account for successfully managing species conservation.

Postepizootic Persistence of Asymptomatic Mycoplasma conjunctivae Infection in Iberian Ibex

The susceptibility of the Iberian ibex (Capra pyrenaica) to Mycoplasma conjunctivae ocular infection and the changes in their interaction over time were studied in terms of clinical outcome, molecular detection, and IgG immune response in a captive population that underwent a severe infectious keratoconjunctivitis (IKC) outbreak. Mycoplasma conjunctivae was detected in the Iberian ibex, coinciding with the IKC outbreak. Its prevalence had a decreasing trend in 2013 that was consistent with the clinical resolution (August, 35.4%; September, 8.7%; November, 4.3%). Infections without clinical outcome were, however, still detected in the last handling in November. Sequencing and cluster analyses of the M. conjunctivae strains found 1 year later in the ibex population confirmed the persistence of the same strain lineage that caused the IKC outbreak but with a high prevalence (75.3%) of mostly asymptomatic infections and with lower DNA load of M. conjunctivae in the eyes (mean quantitative PCR [qPCR] cycle threshold [CT ], 36.1 versus 20.3 in severe IKC). Significant age-related differences of M. conjunctivae prevalence were observed only under IKC epizootic conditions. No substantial effect of systemic IgG on M. conjunctivae DNA in the eye was evidenced with a linear mixed-models selection, which indicated that systemic IgG does not necessarily drive the resolution of M. conjunctivae infection and does not explain the epidemiological changes observed. The results show how both epidemiological scenarios, i.e., severe IKC outbreak and mostly asymptomatic infections, can consecutively occur by entailing mycoplasma persistence.IMPORTANCEMycoplasma infections are reported in a wide range of epidemiological scenarios that involve severe disease to asymptomatic infections. This study allows a better understanding of the transition between two different Mycoplasma conjunctivae epidemiological scenarios described in wild host populations and highlights the ability of M. conjunctivae to adapt, persist, and establish diverse interactions with its hosts. The proportion of asymptomatic and clinical M. conjunctivae infections in a host population may not be regarded only in response to intrinsic host species traits (i.e., susceptibility) but also to a specific host-pathogen interaction, which in turn influences the infection dynamics. Both epidemic infectious keratoconjunctivitis and a high prevalence of asymptomatic M. conjunctivae infections may occur in the same host population, depending on the circulation of M. conjunctivae, its maintenance, and the progression of the host-pathogen interactions.