The spread of Corynebacterium pseudotuberculosis infection to unvaccinated and vaccinated sheep

Abstract

SUMMARY The decrease in the prevalence of Corynebacterium pseudotuberculosis after two generations of vaccination against the disease it causes, was used to estimate the rate of control of caseous lymphadenitis (CLA). Three groups of 150 sheep, of which 50 in each group were artificially infected with C pseudotuberculosis and 100 in each group were uninfected sheep, were run separately for 40 months and shorn 5 times to promote the spread of CLA. One lot of 50 infected sheep and 2 lots of 100 uninfected sheep were vaccinated against CLA. The rate of spread of CLA was recorded. Sheep vaccinated against CLA and naturally exposed to infection had a 74% lower infection rate than unvaccinated sheep. Sheep vaccinated against CLA and exposed to only vaccinated infected sheep had a 97% lower infection rate. Unvaccinated sheep had a 76% infection rate, with 77% of the transmission occurring at the 4th and 5th shearings, without any discharging CLA abscesses being observed. This study supports the view that in Australian wool producing flocks, CLA spreads mainly from sheep with discharging lung abscesses to sheep with shearing cuts. Vaccinated sheep infected with CLA have 96% fewer lung abscesses compared with unvaccinated infected sheep and are therefore less likely to spread this disease to other sheep.

Corynebacterium pseudotuberculosis: microbiology, biochemical properties, pathogenesis and molecular studies of virulence

“…Not infrequently, contaminated sheep cough bacteria onto skin cuts of other sheep, constituting another means of transmission [84,114]. In cattle, as well as in buffaloes, there is evidence of mechanical transmission of this bacterium by houseflies and by other Diptera, though the natural mechanisms of infection with C. pseudotuberculosis are not well documented [97,116,117].…”

“…Paton et al [84], in an analysis of the effectiveness of a combined toxoid vaccine against CLA, reported a reduction in the number and size of CLA lung abscesses and a decrease in the spread of this disease within the flock. However, in another study [85], it was reported that although 43% of the farmers applied commercial CLA vaccines, only 12% used them correctly.…”

“…It is generally agreed that the best strategy to control the disease is vaccination of healthy animals, along with the identification/removal of infected animals [13,71,84,114]. However, the difficulties associated with the early clinical identification of infected animals can be a hindrance to such a strategy.…”

Molecular genotyping of multinational ovine and caprineCorynebacterium pseudotuberculosisisolates using pulsed-field gel electrophoresis

“…In Australia, CLA abscesses in sheep occur most commonly in the superficial lymph nodes of the shoulder and flank. In addition, lung abscesses are postulated to play the major role in transmission of the disease in that country, as C. pseudotuberculosis has been cultured from the tracheas of sheep with lung lesions and observed discharging into airways [15,23,37]. A similar presentation of CLA is recognized by sheep breeders in Canada, but there a visceral form of the disease, although rare in Australia, is regarded as one of the most common causes of ill thrift or "thin ewe syndrome" in adult sheep [29].…”

Diagnostic comparison of Corynebacterium pseudotuberculosis through microbiological culture and PCR in sheep samples

“…Parotideal, mandibular, superficial cervical, subiliac, popliteal, or mammary lymph nodes may be affected. However, in some cases, the disease may be asymptomatic, with internal abscesses in lungs and bronchial lymph nodes, which may cause chronic pneumonia, mesenteric lymphadenitis, and pyelonephritis (Paton et al, 1995). Diagnosis is based on characteristics of the lesions (presence of external abscesses), and these confirmation relies on isolation and biochemical identification, mainly to differentiate opportunistic pathogens that also cause abscesses, such as Arcanobacterium pyogenes and Pasteurella multocida (Dercksen et al, 2000;Dorella et al, 2006).…”