A beef producer lost 2 head of cattle just outside the Gulargambone area out of a mob of 100 in early June 2011. At least 14 others were unwell. All the animals that had died or were sick came from the same paddock. The affected mob consisted of mixed sexes and were about 10 months of age. They were on a plains grass paddock with no supplementary feeding. Some of the animals have been scouring for about 5 days. Cattle were treated with Ivomec pour on in early 2011 and again on the day of the property visit. Cattle are not routinely vaccinated on the property. There was 20mm of rainfall in the previous week. The property was previously affected by severe floods in December 2010. The owner also reported problems in the last couple of months with calf scours unresponsive to antibiotic treatment.
A brief examination was carried out on one of the animals that had died on the way to the yards. The carcass was bloated and profuse foul smelling diarrhoea continued to discharge even after death. Due to limited daylight, a decision was made to forgo post mortem examination and focus on the sick animals instead.
Six of the worst affected animals were examined in the yards. All had severe, projectile, foul smelling diarrhoea. There was obvious loss in body condition with an average body score of 2 out of 5. Temperatures ranged from normal (3 animals); 39.9C (2 animals) and 40.2 (1 animal). The differentials considered in this case were pestivirus, salmonellosis, yersiniosis, plant poisoning and internal parasites. Six bloods and four dung samples were submitted from affected animals for serology and bacteriology respectively.
All blood samples were negative for pestivirus antigen capture ELISA-PACE (BVD). All dung samples were positive on Salmonella culture and identified as Salmonella typhimurium. Further antimicrobial testing identified that this Salmonella species was sensitive to all of the following: ampicillin, trimethoprim, tetracycline, neomycin, and cefuroxime. Resistance was identified to sulphafurazole. Yersinia culture was negative. Faecal egg count (Modified McMaster) on one sample was low with 180epg strongyle; 0epg nematodirus; and negative for tapeworm and coccidia.
Due to the rapid deterioration of animals and the lag time between sampling and obtaining culture and sensitivity results, treatment was initiated early on with long-acting oxytetracycline and oral rehydration/electrolyte fluids.
Bovine salmonellosis is a significant disease that has the potential to cause devastating losses if left untreated. Salmonellosis affects both calves and adult cattle and may present with severe diarrhoea, septicaemia, pneumonia, fever, dullness, anorexia, decreased milk production, abortion and eventually death in some cases (1,2).
Cattle generally acquire salmonella infection via faecal-oral transmission with bacterial shedding occurring in faeces, milk, saliva, and bodily fluids. Some animals may be carriers of the disease. Environmental sources of salmonella infection in cattle have been attributed to contaminated water, soil, poor sanitation of housing facilities, feral animals, birds, rodents, and flies (4,5).
Bovine salmonellosis is a frequent problem in dairy herds, but has also been reported in beef feedlot herds (4,5,6). The infection rate is likely high in these type of production systems because of proximity of animals, communal feed/watering systems, housing systems, and continuous influx of new animals with possible introduction of carrier animals.
On farm risk factors that may have contributed to a salmonella outbreak in this pasture based adult beef herd include: severe flooding followed by subsequent rains in the months preceding, possible runoff into some paddocks, and history of severe calf scours on the property. Various survival times of Salmonella species in the environment has been reported surviving anywhere from 3 to 5 months in contaminated slurries, manure, and soil depending on environmental conditions (5,10,11,12). Water and soil samples were not taken in this case, however they may have been useful in identifying the source of environmental contamination.
Salmonellosis is a zoonotic pathogen and therefore poses significant risks to human health in terms of occupational exposure, food safety, and antibiotic resistance. It is important to educate livestock owners and farmhands regarding hygiene and strategies to minimise the risk of exposure.
Salmonellosis is a global health concern in veterinary and human medicine. In Australia, Campylobacter (15,973 notifications) is the leading cause of food borne related illnesses followed secondly by Salmonella (9,533 notifications) of which Salmonella typhimurium was the most commonly isolated serotype (3).
To reduce the emergence antibiotic resistance from paddock to plate, veterinary practitioners should be prudent when selecting antibiotics for the treatment of salmonellosis in food producing species. Multi-drug resistant salmonella strains is a growing concern overseas with resistance documented in both people and animals (6,8,9). However this strain of Salmonella showed sensitivity to 5 out of 6 antimicrobials tested. This could be due to the infrequent use of antibiotics and veterinary services utilised on this farm.