In June 2008, two cases of Type II ostertagiosis were diagnosed in cattle in the Armidale district of NSW. Type II ostertagiosis is an uncommon syndrome involving the synchronous maturation of large numbers of inhibited Ostertagia ostertagi larvae (Hungerford 2001; Smeal 1995). Elevated plasma pepsinogen concentrations were a key finding in the cases contributing to the diagnosis. In both cases, treatment with macrocyclic lactones (MLs) failed to prevent and/or resolve clinical signs prior to investigation. This raised concerns that resistance in Ostertagia ostertagi to macrocyclic lactones had played a role. (Urbach-Cohn 2009)
A two and a half year old Angus bull presented with a 12-month history of scouring while on good feed and maintaining weight. The bull was drenched with ivermectin two months prior to investigation. The bull was grazing improved pasture of approximately 1500+ kg DM/Ha.
The bull was clinically normal aside from diarrhoea.
|Yersinia pseudotuberculosis||(++ - moderate growth)|
|Elevated Pepsinogen||13.6 U/L (normal 0.0-5.0)|
|Johnes Disease Serology||Negative|
|Faecal Egg Count||Negative|
Lab report comments: "Pepsinogen level is above normal range. This is strongly suggestive of damage to abomasal mucosa".
A four year old bullock presented with a history of scouring, weight loss and 'poor doing'. Doramectin had been used to drench the bullock prior to investigation with no response evident. The bullock was blood tested 16/6/08 and appeared in poor condition. Submandibular oedema was evident. On 27/6/08, the bullock was re-examined, was found to be recumbent, and was humanely destroyed.
|Selenium levels||Normal range|
|Elevated Pepsin||9.8 U/L (normal 0.0-5.0)|
Lab report comment: "The hypoproteinaemia and hypoalbuminaemia is profound and explains the clinical signs. If the animal is dehydrated, the true serum protein will be lower still. Findings are consistent with serious gastrointestinal parasitism. Elevated pepsin supports gastric parasitism and is consistent with type II ostertagiosis".
In Australia, type II ostertagiosis normally occurs in late summer through to autumn. It occurs when large numbers of arrested L4 larvae emerge synchronously from the mucosa. Both this emergence and the subsequent activity of adults in the lumen causes clinical parasitic gastro-enteritis. Type II ostertagiosis generally affects only a small number of mature cattle in a herd. Type II infections are typified by diarrhoea, weight loss, dehydration, submandibular oedema and death.
Both cattle investigated in June 2008 received previous anthelmintic treatment of the ML group with no apparent response.
In case 1, the Angus bull had a concurrent infection of Yersinia however, on advice, was treated 4 weeks apart with an ML and diarrhoea subsequently ceased.
The lack of efficacy of the initial ML application to remove the arrested L4 stage of Ostertagia in both cases is a concern and may indicate an emerging resistance problem.