The number of flocks affected by Salmonella abortion annually is small in the United Kingdom, but within those the losses may be catastrophic, as many animals can be affected in any one outbreak (Linklater, 1983a; Sojka et al., 1983, von Tavel et al., 2005). An increase in the number of reported cases of salmonella incidents has been reported by Defra (Binns and Kidd, undated).
The organisms of the Salmonella group are short Gram-negative rods, which are aerobic and mostly grow well on laboratory media at 37 ° C. Four serotypes of salmonellae have been most commonly associated with salmonella abortion in the United Kingdom: Salmonella abortus ovis, S. montevideo, S. typhimurium and S. dublin. Of these, only S. abortus ovis is host-specific (Linklater, 1991). Half of the 70 abortion incidents involving Salmonella in 2003 were associated with Salmonella enterica subspecies diarizonae (Binns and Kidd, undated).
The general systemic and enteric signs of S. typhimurium and S. dublin infections are profound. The animals are anorexic, have high temperature and scour profusely. Those which do not die of septicaemia may continue to scour and die from dehydration. Pregnant ewes may die from septicaemia before aborting (Linklater, 1991).
Infections with S. abortus ovis and S. montevideo, on the other hand, are more specifically linked to abortion and cause only minor systemic and enteric signs (Linklater, 1983b). Apart from aborting, the ewes generally appear normal unless post-parturient metritis develops due to secondary bacterial infection. Some lambs may be born alive, but these are often sick and may die from Salmonella blood poisoning, starvation, hypothermia or other diseases such as pneumonia.
As S. abortus ovis is host-specific, it is invariably introduced into the flock by an infected sheep (Linklater, 1991). Infections of S. montevideo and other salmonellae can be introduced by many sources, including food, water, other animals and birds (Littlewood, 1984; Sharp et al., 1983, Pennycott et al., 2006). Aborted foetuses and placentae are heavily contaminated with organisms and are rich sources of infection for other animals that eat or lick them (Linklater, 1991).
S. abortus ovis used to be one of the most common causes of abortion, especially in the southwest of England, but has declined in recent years to very low levels, for reasons which are unclear. The number of Salmonella infections associated with S. montevideo has increased during the 1970s and 1980s, but this is still only an occasional cause of abortion (Sharp et al., 1983). A human outbreak of S. Typhimurium in the north of England in 1999 was linked to mutton and lamb from a local abattoir and was unusual in being sensitive to antimicrobial drugs (Purvis et al., 2005).
Salmonellosis is a non-notifiable zoonotic disease (see Defra website Zoonoses: Diseases).
See also NADIS Sheep Disease Bulletin: Salmonella abortion in ewes (Sargison, 2003)
Methods of Control and Prevention
Salmonella abortus ovis usually spreads rapidly through the flock, causing an abortion storm. Immunity develops after infection, and in future years only replacements tend to be affected. Apparent success has been obtained in protecting these by closely mixing non-pregnant females with aborting ewes. This is not ideal under organic management and may lead to more carriers in the flock. Another problem with this method is the spread of enzootic abortion, if it is present in the flock. The best method of preventing Salmonella abortus ovis is to maintain a closed flock (Linklater, 1991), which is promoted in organic farming.
Salmonella montevideo does not usually become endemic and normally, after an episode of the disease, the infection disappears from the flock. Despite the rapid spread of S. montevideo, it may still be useful to isolate affected animals.
In the case of S. montevideo, the reduced stocking rates and outside lambing, advocated in organic farming, may contribute towards reducing the spread of infection through the flock.
With regard to the survival of Salmonella and other zoonotic species in stored manure, temperature is the most important influential factor (Nicholson et al., 2004, Hutchison et al., 2005). Salmonella can survive in stored slurries and dirty water for up to three months although in solid manure heaps where temperatures are greater than 550C survival is less than one month (Nicholson et al., 2005).
Methods of Treatment
There is no effective treatment in the case of S. montevideo by the time signs are seen. In the case of Salmonella abortus ovis, ewes that scour may require supportive therapy with electrolyte solutions. Aborting ewes frequently develop metritis, and injections of antibiotics, preferably short-acting penicillin for several days after the abortion under the supervision of a veterinary surgeon, may help to prevent this (The Henston Vade Mecum, 1998). Treatment sometimes needs to be repeated after 7-10 days (Sargison, 2003). The withdrawal period for meat consumption should be at least twice (Defra, 2006) the period recommended on the product data sheet.
Whenever possible, aborted foetuses and placentae should be submitted for veterinary investigation, but if these samples are not available, vaginal swabs can be useful for the diagnosis of salmonellosis. The diagnosis is confirmed by the bacterial culture of Salmonella sp. from the placenta or foetal stomach contents (Sargison, 2003).
For most recent information on different sector body requirements on withdrawal periods for livestock products following medicinal use please see
The Disease and Welfare
Apart from aborting the ewes generally appear normal unless post-parturient metritis develops due to secondary bacterial infection. The aborting ewes should therefore be injected with long-acting antibiotics under veterinary supervision to prevent suffering from metritis. Some lambs may be born alive, but are often sick and may die from salmonella blood poisoning, starvation, hypothermia or other diseases such as pneumonia. Some lambs may have to be humanely destroyed after the abortion to prevent further suffering.
Good Practice based on Current Knowledge
Maintain a closed flock policy.
In the case of an outbreak of Salmonella abortus ovis, make sure infection spreads throughout the flock after lambing to build up immunity and contain the abortion storm to only one season. Bought-in livestock should be mixed with the infected flock prior to mating to build up immunity.
In the case of an outbreak of Salmonella montevideo, affected ewes should be isolated to prevent the disease from spreading, products of abortion should be removed and hygienic precautions should be taken to avoid spread of infection to clothing, equipment and other groups of sheep.
Movement of heaps of livestock bedding waste from animal pens to a secondary store, and storing them under conditions conducive for increased temperature is a simple and cost-effective treatment for rapidly lowering levels of zoonotic agents in solid farm wastes.
Moving and turning over of troughs between feeding may reduce contamination by birds (Sargison, 2003).
Binns, S and Kidd, S (undated) Salmonella in Livestock Production in GB 2003. Centre for Epidemiology and Risk Analysis, Veterinary Laboratories Agency. Available at: http://www.defra.gov.uk/corporate/vla/science/documents/science-salm03-intro.pdf
Defra (2006) Compendium of UK Organic Standards. Available at http://www.defra.gov.uk/farm/organic/standards/pdf/compendium.pdf
Hutchison ML, Walters LD, Avery SM, Moore A (2005) Decline of zoonotic agents in livestock waste and bedding heaps. Journal of Applied Microbiology 99 (2): 354-362
Linklater, K. A. (1983a): Abortion in ewes due to Salmonella montevideo. Proceedings of the Sheep Veterinary Society 7: 16-18.
Linklater, K. A. (1983b): Abortion in sheep associated with Salmonella montevideo infection. Veterinary Record 112: 16, 372-374.
Linklater, K. A. (1991) Salmonellosis and Salmonella Abortion. In: Diseases of Sheep. 2nd edition. Ed.W. B. Martin and I. D. Aitken. pp. 65-70. Blackwell Scientific Publications, Oxford.
Littlewood, J. B. (1984): Salmonella montevideo-a cause of abortion in sheep. The State Veterinary Journal 38: 112, 36-39.
Nicholson FA, Chambers BJ, Moore A, Nicholson RJ, Hickman G (2004) Assessing and managing the risks of pathogen transfer from livestock manures into the food chain. Water and Environment Journal 18 (3): 155-160
Nicholson FA, Groves SJ, Chambers BJ (2005) Pathogen survival during livestock manure storage and following land application. BioResource Technology 96 (2): 135-143
Pennycott TW, Park A, Mather HA (2006) Isolation of different serovars of Salmonella enterica from wild birds in Great Britain between 1995 and 2003. Veterinary Record 158 (24): 817-820
Sargison, N (2003) : Salmonella abortion in ewes. NADIS Sheep Disease Bulletin.
Sharp, J. C. M. Reilly, W. J. Linklater, K. A. Inglis, D. M. Johnston, W. S. Miller, J. K. (1983): Salmonella montevideo infection in sheep and cattle in Scotland, 1970-81. Journal of Hygiene 90: 2, 225-232.
Sojka, W. J. Wray, C. Shreeve, J. E. Bell, J. C. (1983): The incidence of Salmonella infection in sheep in England and Wales, 1975 to 1981. British Veterinary Journal 139: 5, 386-392.
The Henston Large Animal and Equine Veterinary Vade Mecum (1998): 10th edition. Henston Veterinary Publications. Veterinary Business Development Ltd. Peterborough, UK.
UKROFS (2000): UKROFS Standards for Organic Food Production. UK Register of Organic Food Standards. Room 320C C/O MAFF, Nobel House, 17 Smith Square, London SW1P 3JR. Standards
von Tavel L, Fivian R, Kirchhofer M, Boujon P, Hirsbrunner G (2005) Abortion in sheep: Epidemic Salmonella Abortusovis outbreak 2005 in Switzerland. Schweizer Archiv Fur Tierheilkunde 147 (10): 445-452