Clostridium sordellii is one of the anaerobes responsible for malignant oedema, a wound infection of sheep, cattle and other species that develops in the subcutaneous fascia and causes an acute fatal toxaemia. Clostridium septicum is the most common causal agent but C. chauvoei and C. novyi have both been implicated while C. perfringens type A and C. sordellii are less frequently isolated (Beveridge WIB, 1983).
However, elsewhere, C. sordellii has been isolated from a number of new syndromes; in Europe and the Middle East, sudden death in sheep of all ages, acute abomasitis in calves and young lambs, haemorrhagic enteritis, sudden death and abomasitis in finishing lambs (Lewis and Naylor 1998, Vatn et al 2000, Akan et al 2008) fatal peri-parturient disease in ewes (Lewis 2007) and in New Zealand, sudden death in sheep and growing cattle (West et al 2009, Vermunt et al 2010).
Approximately 400 2-3 month old mixed sex merino lambs were marked in early October 2014. The lambs were not vaccinated at marking and the ewes had not been vaccinated pre-lambing. Four days later, 15 of the 200 male lambs in the mob died and several more were sick, while none of the 200 females died or were observed to be sick.
The mob was examined in the paddock. Several male lambs were reluctant to walk. One was found in lateral recumbency, alert but unable (or reluctant) to stand. On examination this lamb had a marked swelling of the subcutaneous tissues of the ventral abdomen with purplish skin discolouration at edges of the swelling. This lamb had a moderately swollen scrotum with the ventral third of the scrotum surgically removed consistent with castration.
A recently castrated 25 -30 kg, 3-4 month old merino was euthanased and necropsied. The most remarkable finding was the extensive clear brownish ventral, subcutaneous oedema extending from the inguinal area to the brisket (figures 1, 3). On incising the scrotum the scrotal sac was found to be lined with thickened, red to purple tissue with brownish oedema fluid visible in the spermatic cord most notable around the testicular lymph node (figure 4).
Routine culture of the oedematous, subcutaneous fascia grew no bacteria while routine culture of the infected scrotum grew a moderate mixed growth including Trueperella pyogenes. Anaerobic cultures of both the fascia and the scrotum grew a profuse growth (pure and predominant respectively) of Clostridium spp. A smear of the pure culture grown from subcutaneous tissue was submitted for clostridial fluorescent antibody testing. The sample was negative for C. chauvoei, C. novyi type B and C. septicum but was positive for C. sordellii.
Approximately 50 lambs were treated intramuscularly with 5 ml of penicillin (procaine penicillin 150mg/mL, benzathine penicillin 150mg/mL and procaine hydrochloride 20mg/ml, Benacillin, Ilium). The mob was also vaccinated with 5:1 clostridial vaccine. While this treatment curtailed losses, it is of interest that C. sordellii antigens are not included in standard 5 in 1 vaccines, so the vaccine was presumably not protective.
Traditionally, C. sordellii is one of the anaerobes associated with malignant oedema in cattle and sheep. However, in Europe, Turkey and New Zealand, it has emerged as a cause of a range of new or newly described diseases, most notably abomasitis and sudden death in sheep and cattle. In a pattern reminiscent of enterotoxaemia, deaths are most often seen in rapidly growing animals often associated with a change of diet and high dietary carbohydrate. Like braxy (caused by Cl septicum), abomasitis may be seen in sheep grazing root crops and new pastures, suggesting that soil borne spores may contribute (Lewis 2007).
In cases of abomasitis, the abomasal mucosa is congested, eroded and sometimes ulcerated while the abomasal wall is oedematous and emphysematous. Erosions and congestion are present in the abomasal mucosa. While cases in older sheep are less defined, there may be peritonitis and abomasal ulceration.
In cases of sudden death, there is evidence of toxaemia and rapid autolysis. In New Zealand, young, rapidly growing cattle on highly digestible pastures are most susceptible (Vermunt et al 2010).
Unlike some other species of Clostridia, C. sordellii is not a normal component of gut flora, but it is widespread in the environment and can invade wounds and tissues pre and post mortem. Because of the possibility of post-mortem invasion, its isolation alone is not sufficient evidence to confirm causation. Vermunt et al (2010) therefore cautioned that, before a diagnosis of C. sordellii sudden death is made, frothy bloat should be excluded and that C. sordellii should be isolated from liver and muscle sampled shortly after death. In this case C. sordellii was isolated in pure growth from subcutaneous tissue obtained immediately after euthanasia, confirming its role in the outbreak (bearing in mind that only one lamb was necropsied).
In New Zealand and the United Kingdom, but not in Australia, vaccines containing C. sordellii antigens are available to prevent this disease (West et al 2009, Lewis 2007). Given that C. sordellii is not commonly diagnosed in Australia this seems reasonable, but it is also possible that the other disease manifestations occasionally occur here without diagnosis.