Volume 22 • Issue 04 • 2018 flora is necessary for a well-functioning intestine . RL - 29 June 2018
E . coli virulence factors . There are hundreds of strains of E . coli , and some are only environmental opportunists and others are true pathogens . Distinguishing between environmental and pathogenic strains has not been possible for years , as serotyping is no longer being carried out at Onderstepoort . Serotyping to establish pathogenicity had limitations , and has become outdated . Research has found that PCR testing for virulence factors gives superior results . These tests have been available in South Africa for E . coli strains isolated from man for some years , but not for animal isolates until recently .
E . coli virulence factors code for attachment and toxin production . The attachment factors or adhesins allow pathogenic E . coli to attach to the intestinal wall or bladder epithelium , so that they are not washed out with the ingesta or urine . E . coli toxins are responsible for the signs and lesions seen , such as enteritis , haemorrhage , oedema and ulceration . There is a measure of tissue and target cell specificity , making many of the virulence factors species , age and site specific .
We now have 5 E . coli virulence factor panels available . Each panel tests for 4 or 5 factors .
• Ruminant panels [ 2 ] for cattle , sheep and goats . The first panel is more suitable for calves , lambs and kids under a week of age , and both panels are advised for older animals . The two panels could be used for diagnosing and differentiating between enterotoxigenic E . coli , which does not need antibiotic treatment , and enteropathogenic E . coli which is best treated with an appropriate antibiotic . Virulence factor based vaccines , apart from K99 in Scourguard and Rotavac Corona , are not yet available for ruminants . However , once the offending virulence factors are known , appropriate autogenous vaccines can be prepared .
If no virulence factors are detected , one may be certain that the E . coli isolate is only an opportunist . This would be particularly helpful for veterinarians battling with the current Cryptosporidium / E . coli outbreak in ruminants . Many autogenous vaccines that were prepared were not effective , and only a handful of autogenous vaccines prevented further diarrhoea .
It is of course crucial that the correct colonies of E . coli are selected for the virulence factor tests , and not contaminants , by an experienced microbiologist , to prevent fruitless expenditure on the test .
DIAGNOSIS
NF - 19 June 2012
MSD import a kit that can test for Rota , Corona , pathogenic E . coli ( F5 K99 attachment factor ) and Cryptosporidium . These tests are accurate and widely used in the EU and Australia . In Australia they use this test and if negative send it off for Salmonella culture .
We also visited a virus lab at MEDUNSA . They specialize in Rota virus identification , irrespective of species involved . The current available vaccines contains 4-5 strains but we are not sure if the strain affecting our calves are in this vaccine . This lab can identify the specific strains for us at no cost .
JW - 14 Nov 2012
With regards to specimens . Contact the laboratory you use for guidance . When investigating a herd diarrhoea problem , I would advise you to submit specimens from clinical cases in the acute phase before treatment ( as pointed out by others ), as well as faeces from 5 ? healthy individuals ( same age group ) for examination .
You can find Cryptosporidium , nematode eggs , viruses , Coccidia oocysts , etc in healthy and diseased animals , and comparing the findings may assist with getting to the answer . Especially if you cannot identify the Coccidia oocysts and / or nematode eggs .
DM - 14 Nov 2012
Should also be picked up in smear rather than flotation . Under 1 week of age ? What is its incubation period ?
GH - 14 Nov 2012
Pre-patent and patent period in calves range from 3 to 6 , and 4 to 13 days in neonatal period . Bradford Smith . Stay sick for 4 to 14 days and the excretion of oocysts ( VERY small ) has been described as short as 2 days of age .
Forgot to say , cannot see in smear because it is very small ( smear too contaminated and the oocyst can be confused with many other things
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