Mycoplasma conjunctivae infection is self-maintained in the Swiss domestic sheep population
Introduction
Infectious keratoconjunctivitis (IKC) is recognised worldwide as a common condition affecting the eyes of domestic sheep (Jones, 1991). The disease usually involves only the surface of the eye, with the first clinical signs being conjunctivitis, resulting in lachrymation, blinking or blepharospasm. The disease may progress and involve the cornea, and sometimes the keratitis is extensive. In these cases vision is seriously, if only temporarily, impaired. The IKC is then a nuisance to farmers since animals require treatment and some nursing to reduce the period of blindness (Egwu et al., 1989).
The term IKC is used to describe a clinical condition which is apparently not always ascribable to the same infectious agent (Jones, 1991). Pathogenicity of M. conjunctivae has been demonstrated in domestic sheep (Jones et al., 1976, van Halderen et al., 1994), domestic goats (Trotter et al., 1977), and Alpine ibex (Capra i. ibex, Giacometti et al., 1998). This agent has also been implicated as etiological agent of IKC in other Caprinae species such as Alpine chamois (Rupicapra r. rupicapra, Nicolet and Freundt, 1975, Degiorgis et al., 2000) and mouflon (Ovis orientalis musimon, Terrier, 1998). Mycoplasmal IKC is highly contagious within herds (Baas et al., 1977), and transmission occurs predominantly by contact or by vectors (Jones, 1991). On alpine meadows, interspecific transmission of M. conjunctivae is likely to occur (Degiorgis et al., 1999), and an interrelationship between domestic and wild Caprinae species has been considered in IKC (Nicolet and Freundt, 1975, Giacometti et al., 1997).
In Switzerland, other species susceptible to M. conjunctivae infections are domestic goat, Alpine chamois, and Alpine ibex. The Swiss goat population amounts to approximately 57,000 animals kept in 8500 flocks (Anonymous, 1994). Free-ranging chamois populations (>100,000 animals) are present in the mountainous and hilly regions of Switzerland (Alps and Jura mountains). Alpine ibex populations (approximately 15,000 animals) are essentially restricted to scattered high-located alpine areas (Giacometti, 1997). The Swiss plateau is not populated by these wild Caprinae species. During summer, encounters between domestic and wild Caprinae are not infrequent events on alpine meadows (Degiorgis, 1998).
In domestic sheep in Europe, M. conjunctivae infections have been identified in many countries including Croatia (Naglic et al., 1998), Switzerland (Nicolet et al., 1974, Giacometti et al., 1997), the Netherlands (ter Laak et al., 1988), and the United Kingdom (Jones et al., 1976, Hosie, 1988, Egwu et al., 1989). However, its prevalence is not well known in most countries. This may be due to the technical difficulties for M. conjunctivae detection. Culture of M. conjunctivae from ocular swabs is cumbersome and requires specialised technical experience (Jones, 1991). Therefore, new methods for rapid and specific detection of M. conjunctivae-infections such as a nested PCR (based on the 16S rRNA to be performed on conjunctival swabs, Giacometti et al., 1999) and an indirect antibody ELISA test (Belloy et al., 2001) have recently been developed.
In Switzerland, the domestic sheep population was hypothesised to act as reservoir of the M. conjunctivae-infection (Giacometti et al., 2000), but this status is still unproven. The objectives of this study were therefore (i) to assess the occurrence of M. conjunctivae in domestic sheep in Switzerland and (ii) to evaluate the period for which individual sheep are carriers of M. conjunctivae. We performed etiological and serological investigations on affected sheep herds, analysed a stratified random sample of sheep herds using an indirect ELISA and studied lambs experimentally infected with M. conjunctivae.
Section snippets
Domestic sheep populations in Switzerland
The last federal domestic livestock census was performed in 1993 and revealed 20,180 sheep holders and a total of 424,027 domestic sheep living in Switzerland (Anonymous, 1994). Most of the holders (77.8%) owned 1–25 sheep, and mean herd size was 21 sheep (Table 1). Most common breeds were Swiss White Alpine, Swiss Oxford Down, Swiss Black–Brown Mountain, and Valais Black Nose. More than half of the Swiss sheep herd (51.8%) is held in four out of 26 cantons (Valais, Berne, Grisons, Saint Gall).
Detection of M. conjunctivae
To verify the presence of M. conjunctivae in domestic sheep in Switzerland we have analysed conjunctival swabs taken from sheep affected with IKC (Table 2). Clinical signs were generally mild and included conjunctivitis and lachrymation. Among a sample of 69 sheep from 21 herds in three Swiss cantons, M. conjunctivae was identified 53 times (76.8%), and 18 sheep herds (85.7%) tested positive. In 1994–1995, 20 M. conjunctivae-strains were isolated from conjunctival swabs. Sensitivity of the
Discussion
In Switzerland we commonly identified M. conjunctivae from the eyes of domestic sheep showing clinical signs of IKC. This agent was detected in the alpine region as well as in the Swiss plateau as previously reported by Nicolet et al. (1974). M. conjunctivae was recovered throughout most of the year including winter. Occurrence of M. conjunctivae-induced IKC in winter was previously reported by Nicolet et al. (1974), Jones et al. (1976), Hosie (1988), and ter Laak et al. (1988).
Using
Conclusions
We conclude that M. conjunctivae is widespread in domestic sheep in Switzerland. In this country, mycoplasmal IKC was found to be endemic and self-maintained in the domestic sheep population. Our results indicate further that lambs may play a key role in the maintenance of the M. conjunctivae infection. Further investigations are necessary to assess risk factors for infection maintenance and to develop tools for the control of M. conjunctivae infections in domestic sheep.
Acknowledgements
The authors are grateful to P. Ratti, K. Jörger, H.-J. Blankenhorn and P. Hauenstein who supported research on IKC. We thank the Swiss Federal Veterinary Office, Liebefeld, for enabling access to the serum bank, M. Engels for the management of serum samples, and many sheep breeders for enabling sampling of their animals. We also wish to thank T. Fuchs, T. Hummel, D. Mayer, H. Maurer, P. Odermatt, G. Regi, M.-P. Ryser-Degiorgis, and B. Stübi for sampling some of the sheep, M. Krawinkler and Y.
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