Studies on vero (shiga) and LT toxin producing wscherichia coli infections in animals and man

Abstract

A study was undertaken to investigate the role of enterotorigenic Escherichai coliin animals and human diarrhoeal dicease with special emphasis on cattle, in Sri tanka. Two approaches were adapted to study the epidemiclogy of Verocytotonin and heat-labile toxin producing Escherichia coli. A} A cress—sectional study where faecal samples from cattle, 5 goat, pigs ano man were screensed for Verocytotosxin (VT) and Heatlabile {(LT)-producing E.coli and serum samples were tested for the prevalence of VT and LT antibodies respectively. B) A longitudinal study to monitor the prevalence of VTEC and LTEC in calves. This study revealed that WMT-producing Escherichia coli (MTEC) strains wers highly prevalent in cattle. In the cross sectional study, 27% diarrhoeic and 4.5Z non-diarrhoeic calves shed NTEC in the faeces. In the longitudinal study, s11 26 animals with two excm pticns, followed for a periocd of 2-6 months shed VTEC at least once in their faeces. Although a significant association between VTEC and diarrhoea was seen in calves aged less than 10 weeks. the high prevalence of VTEC in healthy calves indicates that furiher studies are reguired to definitively incriminate the role of VTEC in calf diarrhoea. The cseroepicdemiclogical study also revealed that VTEC are very commong amongst cattle population in 5ri Lanka and that the seropositivity in these animals seems to be in response to VT1 VTEC but not toc VT2, No VT neutralising antibodies could be demonstrated in human sera in the present study. The serotyping and DNA probe results revealed that calf VTEC strains produce ¥T1; VT2 or both, and that there is a wide diveersity of VTEC serotypes.The longitudinal study revealed an apparent stability of YT genotype {(VT1/VT2) in a given serotype. The distribution of VTEC positive colonies in primary faecal culture plates from 22 calves showed that the detection of positive colonies varied from 1/10 to 10/10 colonies tested. Further, testing a pool of ten colonies gave similar results to that of screening all ten colonies individually. This is an useful approach where multiple colonies are required to be tested in order to detect a low prevalence of VTEC in stools. Thirteen per cent of a small sample of 20 diarrhoeic goats shed VTEC in their faeces, whilst only 2 % of humans with diarrhoea and 2% of non-diarrhoeic pigs shed VTEC in their faeces. Seroepidemiology for L' ¥ 5 these species also indicatated a low prevalence of VTEC. While 11 -12 7% of cattle (diarrhoeic and non-diarrhoeic) shed LTEC there was nc significant association of LTEC with diarrhoea. Screening of faecal samples and the subsequent DNA probe results on LTEC isolated from cattle showed that LT2 (a newly described class of LT) were the only type of LT produced by these strains. This was supported from serocepidemiological data from cattle, where 41 per cent of the sera tested had antibodies to LT2 and only 9 per cent to LTi. LTEC strains were recovered from 38 per cent of diarrhoeic and 16 per cent of non-diarrhoeic pigs and from only 1 per cent of diarrhoeic humans. In contrast, seroepdimioclogical data from humans indicate a high prevalence of LT1 antibody (72 %) in human <era. Thie indicates that LTEC might play a role in diarrhoea in humans in Sri Lanka.