key: cord-0008466-mygbyy1v
authors: Tzipori, Saul
title: Economically significant enteric infections in domestic animals in Australia
date: 2007-11-19
journal: Br Vet J
DOI: 10.1016/0007-1935(88)90021-8
sha: eb66043b10e28296ab7cf3ee0988512420d163e6
doc_id: 8466
cord_uid: mygbyy1v

nan

The predominant causes of diarrhoea in farm animals in Australia are discussed in relation to their relative contribution to disease . Control strategies to some of them are briefly assessed in the context of their economic impact . As in other developed countries the economic significance of diarrhoea in young domestic animals in Australia has emerged with intensification of animal industries . However, the extent of the problem in Australia has never reached the dimensions experienced by animal producers in North America and Europe . The three main interrelated factors responsible for this difference include climate and management and the absence of certain pathogens . In cattle and sheep, low stocking rate and milder winterrequiring less protective housing-influence the degree of crowding of newborn animals which, in turn, reduce the risk of exposure to infection at a susceptible age . For example, diarrhoea due to strains of enterotoxigenic Escherichia coli (ETEC) which affect newborn calves and lambs, is infrequently encountered in Australia . Of the five most important enteric pathogens of piglets found worldwide, only one is a major cause of neonatal and post-weaning mortalities in Australia .

Over the last decade the incidence and the economic significance of calf diarrhoea in Australia has fluctuated considerably . The economic burden of the disease, particularly in beef herds, during 1974-75 was considerable . However it declined in the following decade because of a combination of factors : a severely depressed market led to decline in the value of animals, and several successive years of drought led to reduction of the number of cattle from a peak of 30 million in 1976 to below 20 in the following decade .

Diarrhoea in calves is generally attributed to bovine rotavirus, certain stable toxin (ST) producing ETEC, bovine coronavirus, Cryptosporidium, Salmonella sp . and bovine viral diarrhoea (BVD) . Most instances in Australia, however, are attributed to two agents, namely bovine rotavirus and Cryptosporidium, which are responsible for 70-85% of nonbloody diarrhoea occurring in calves aged between 3 days-and 3 weeks (unpublished data) . Bovine coronavirus has been detected in Australia but the strains tested appear to be avirulent and are not commonly encountered in diarrhoeal cases . ETEC strains, as mentioned earlier, are widespread in Australian herds but are not considered a major cause of diarrhoea . Salmonellosis and BVD are responsible for sporadic cases of diarrhoea mostly in older calves .

The technology for production of vaccines against calf rotavirus and Cryptosporidium is available (Saif et al., 1983 ;  Tzipori, unpublished data) . However, in the present economic climate, vaccination against calf diarrhoea is not considered cost-effective . Treatment of several sick calves with rehydration and supportive therapy is cheaper . It is worth stressing that antibiotics are ineffective in the treatment of calf diarrhoea which essentially is attributed to viral or protozoan infections . Antibiotic therapy may have some benefit in diarrhoea that occurs in the first 2 days of life . Br. vet. J. (1988) . 144, 5 2 1 Piglet enteritis Economically, piglet enteritis is a much more serious disease than calf diarrhoea . It tends to be endemic in herds and ranks high among the diseases affecting production . Yet Australia, by contrast to other major pig producing countries, is fortunate . Of the known important pathogens responsible for major epidemics of diarrhoea worldwide, such as transmissible gastroenteritis (TGE) and porcine epidemic diarrhoea (PED) viruses, Clostridium perfringens type C, and Isospora suis, only strains of pig ETEC are significant (Tzipori, 1985) . TGE, a coronavirus, is the most important cause of neonatal pig mortalities in parts of North America, Europe and the Far East . PED, another coronavirus unrelated to TGE, is responsible for major epidemics in some parts of Europe including the UK . Cl. pernfringens type C causes severe necrotizing enterocolitis in newborn animals particularly in piglets . However, the infection tends to be enzootic in certain geographical locations in North America and Europe . None of the abovementioned enteric pathogens occurs in Australian herds .

Isospora suis, a coccidian parasite, has emerged as an enteric pathogen of piglets in North America and Europe only in the last decade . The disease is characterized by high morbidity and low mortality in animals aged between 5 and 15 days . It has been detected infrequently in Australia . The role of porcine rotavirus remains controversial : although it is widespread in herds worldwide, including Australia, the virus appears to induce severe illness only in artificially reared piglets . Extensive epidemiological investigations of this infection in herds did not show the virus to be directly associated with outbreaks of diarrhoea in piglets .

By far the single most important group of enteric pathogens affecting piglets in Australia is ETEC . Most ETEC serotypes reported elsewhere have been detected here . They occur in various combinations of enterotoxins and colonizing factors . Certain ETEC serogroups cause diarrhoeal illness immediately after birth while others cause diarrhoea immediately after weaning (Tzipori, 1985) .

In the absence of the above-mentioned enteric pathogens, control of ETEC infection should lead to reduction in the incidence of piglet enteritis in Australia . Of the various methods that have been suggested in the past including breeding of genetically resistant animals, vaccination appears to be the most effective at present . There are several different approaches to vaccination which will not be discussed here . Vaccination so far, however, has been shown to be effective against neonatal diarrhoea only . The most effective are the new generation of parenteral vaccines containing several colonizing factors produced by recómbinant DNA (Clark et al., 1985) . These are now available in Australia. Autologous vaccines utilizing ETEC strains that are endemic in specific herds have also been used in Australia with varying success (A . V . Fahy, personal communication) . The latter tend to be cheaper, easy to produce, and tailored to the needs of specific herds ; they are less safe when fed as live cultures to animals .

Diarrhoea in lambs is less common than in other domestic species . In Australia it is even less common than in other sheep producing countries . Lambs appear to be more resistant to the range of enteric pathogens affecting piglets and calves ; they are susceptible to ETEC for only a day or so after birth, and after 4 days and 15 days of age they become clinically resistant to infections with rotavirus and Cryptosporidium, respectively (Tzipori, 1985) . Diarrhoea occurs more frequently after weaning in which infectious agents appear to be only one of several other non-infectious factors .

The interaction between infectious agents and the environment in which they perpetuate is dynamic . As climatic conditions and management procedures on farms change over a period, so will the incidence of disease caused by certain pathogens without necessarily a corresponding change in the prevalence of the infectious agents responsible . We have seen the emergence of pathogens such as Isospora suis not encountered a decade earlier, or the almost disappearance of swine dysentery in this country for nearly two decades . It is therefore important to point out that the situation described above may not prevail in a decade from now . This is particularly likely when large scale vaccination against several prominent enteric pathogens is intensified . We have already witnessed, presumably under the pressure of vaccination, reduction in the frequency of isolation of ETEC strains with K88 and a corresponding increase of strains with K99 in pig herds in Europe (Soderlind et aL, 1982) .

Infectious diarrhoea in the young

Advances in Veterinary Science and Comparative Medicine 29, 103 . SAUL TZIPORI, Royal Children's Hospital