Age affected: Weaners, human risk.
Causes: Virulent E. coli strains, Campylobacter or Salmonella: dietary problems; stress; mismanagement.
Effects: Scour within 10 days of weaning.
Weaning in the pig is accompanied by the withdrawal of milk and the protective local antibody that it contains. There is a change in diet, but for many pigs, starter creep feeds given before weaning are very digestible and are not changed for the first week or two after weaning. The combination of withdrawal of milk antibody, the presence of less well-digested food in the gut and mixing following weaning results in an increase in pathogenic Escherichia coli and leads to post-weaning diarrhoea. The strains of E. coli responsible adhere to the cells lining the small intestine by means of fimbriae (hair-like processes), most often the K88 or F4 fimbriae, and secrete an enterotoxin (usually Heat labile Toxin, LT) which causes loss of chloride ions and the secretion of fluid to cause the diarrhoea. E. coli is the first organism to cause diarrhoea in the post-weaning period, but other agents follow. They include strains of rotavirus which multiply in the cells lining the small intestine, destroy absorptive cells and produce atrophy of the intestinal villi (finger-like processes). Bacteria such as campylobacters and salmonella and the protozoan parasite Cryptosporidium, may all contribute to diarrhoea in this age group.
Mode of transmission
Post-weaning diarrhoea may result from the mixing of pigs carrying the E. coli strains usually responsible with susceptible animals at weaning. Infection is also transmitted directly from older, affected or recovered pigs by faecal contact. The organism survives well in the environment, so spread can occur indirectly by contact with contaminated pen furniture, implements or clothing. The other diarrhoeal agents found in this age-group can also be transmitted in similar ways. Introduction to a farm is usually by means of carrier pigs, but can be by clothing, vehicles or footwear which have been contaminated with infected faeces.
Post-weaning diarrhoea occurs within 10 days of weaning, often within 4-5 days. Affected pigs pass greyish, brownish, or watery diarrhoeic faeces with no traces of blood. Haemorrhagic diarrhoea is extremely uncommon. Mucus is rarely present. The diarrhoea is usually transient and resolves within 3-5 days but it may persist, and deaths from dehydration or septicaemia may occur in adverse husbandry conditions. In some cases fever (up to 40.6˚C, 105˚F) may occur over a period of 4 or 5 days and affected animals may be off their feed and depressed. Chronic post-weaning enteritis may cause permanent stunting in recovered pigs. Faeces may be difficult to see in flat decks or in veranda houses, but it can be seen in the feeders in flat decks and the corners of the dunging areas in veranda houses in fully-slatted accommodation. Where inspection is difficult, affected animals may be identified by their dehydrated appearance, and perineal staining. 20-50% of all weaned pigs may be affected, but mortality from the uncomplicated disease is less than 10% or those affected unless complications occur. Even when diarrhoea is only transient, marked reduction in the rate of daily live weight gain may occur in the remainder of an affected group.
The clinical findings of a grey-brown watery diarrhoea 3-5 days after weaning are typical of post weaning diarrhoea. The causal agent is usually E. coli when the diarrhoea begins within 3-5 days of weaning or immediately after the first dietary change after weaning. Enterotoxigenic E. coli can be cultured in pure culture from faecal samples. The other agents which may be present in post weaning diarrhoea are: rotavirus (common); TGE or PED virus (rare at present); Campylobacter (common); Salmonella (uncommon) and Cryptosporidium (frequent). All may be demonstrated in faecal samples or intestinal contents of affected pigs by laboratory examination.
Carcases of animals which have died from E. coli diarrhoea are dehydrated and their eyes are sunken. The liver is dark, the stomach full of feed and the small intestine is dilated and congested with watery, buff-coloured contents. The mucosal epithelium (lining) is reddened and the villi are intact. Mesenteric lymph nodes are enlarged and pale. The large intestines contain fluid faeces or are empty. In freshly-killed piglets, the villi appear intact, are often congested and may be covered with adherent bacteria. Pure growths of pathogenic E. coli can usually be isolated from the anterior small intestine but not from other organs outside the gut.
Treatment and prevention
Treatment is by water medication with ampicillin, amoxicillin, apramycin, neomycin, tetracyclines, trimethoprim sulphonamide, spectinomycin, gentamicin and cephalothin or ceftiofur (where registered). Treatment should be continued for 3-5 days and should be started as soon as clinical signs are noted. In feed medication with chlortetracycline, oxytetracycline, apramycin, neomycin, sulphonamide, trimethoprim sulphonamide and enrofloxacin at therapeutic levels can also be given for at least 10 days. Diarrhoeic piglets should be supported with warmth and oral rehydration and pens disinfected. If there is no response to treatment, re-examine the diagnosis and confirm that the E. coli is still antimicrobial sensitive. Post-weaning diarrhoea can be controlled by maintaining an even temperature for the first week post weaning. Treat affected piglets promptly. Avoid changing feed at weaning, reduce the quantity of feed slightly and consider totally digestible diets. Medication at treatment level may be given over the period of risk. Zinc oxide reduces post weaning diarrhoea when incorporated in post weaning rations at levels of 3.2 kg to give 2600 ppm zinc in the ration for 2 weeks. Piglets may be vaccinated against E. coli by injection but protection may not be complete.
While the E. coli responsible for most cases of Post-weaning Diarrhoea is not a risk to human health, salmonella and campylobacters may be present in the diarrhoea and pose a risk to health. Hygienic precautions should be observed.