Experimental infection of normal and immunosuppressed pigs with Pseudomonas pseudomallei

Abstract

A single dose of 5 x 10(8) bacilli of Pseudomonas pseudomallei by intratracheal injection resulted in acute (21 cases) or chronic (19 cases) melioidosis in 40 of 48 pigs. Fifteen (10 acute and 5 chronic) had been immunosuppressed by cyclophosphamide before inoculation. The major clinical signs were initial fever, marked neutrophilia and, in the acute cases, respiratory distress. There were no signs of the nasal and ocular discharge, paresis or diarrhoea seen in acute cases in south-east Asia. The cyclophosphamide treatment caused a significant decrease in the neutrophil count by 7 d after inoculation in all 15 immunosuppressed pigs, and all were culture positive at necropsy. Eight of the 33 non-treated pigs were culture negative at necropsy. Pigs overcoming the initial phase of infection had more abscess-like nodules that were bacteriologically sterile at necropsy than the pigs with acute cases of melioidosis. P. pseudomallei was isolated predominantly from the spleen, lungs and the injection site. Although only one strain was used in this study, it is likely that Australian strains of P. pseudomallei are not as virulent as the south-east Asian isolates.

Melioidosis in Animals: A Review on Epizootiology, Diagnosis and Clinical Presentation

“…The pig (Table 1) is considered to have a high natural resistance to B. pseudomallei (Thomas et al., 1981, 1990; Ketterer et al., 1986). Cases have been reported from Vietnam, Malaysia and Australia (Retnasabapathy, 1959; Nguyen, 1961; Ketterer et al., 1986).…”

Development of novel animal infection models for the study of acute and chronic Burkholderia pseudomallei pulmonary infections

“…There is an intravenous challenge model of infant pigs that results in a chronic lung infection [11]. However, pigs are not particularly susceptible to B. pseudomallei infections via the intranasal route, and there is only one report on the production of a successful infection after intratracheal injection [12]. Liu and colleagues [13] used C57BL/6 mice to examine infection through the intranasal route in a murine model to imitate infection through inhalation.…”

Pathogenesis of percutaneous infection of goats with Burkholderia pseudomallei: clinical, pathologic, and immunological responses in chronic melioidosis

“…Pigs have repeatedly been shown to be very resistant to experimental infection – even with immunosuppression (Stanton & Fletcher ; Thomas et al . ; Najdenski et al . ), such that they do not appear well suited for the study of melioidosis.…”

“…Natural infection in pigs is typically chronic or asymptomatic (discovered only at slaughter) and likely follows oral infection (Sutmoller et al 1957;Laws & Hall 1963;Omar 1963; Thomas et al 1981;Ketterer et al 1986;Millan et al 2007). Pigs have repeatedly been shown to be very resistant to experimental infectioneven with immunosuppression (Stanton & Fletcher 1932;Thomas et al 1990;Najdenski et al 2004), such that they do not appear well suited for the study of melioidosis. Natural disease in several species of NHPs has been reported as well (Sprague & Neubauer 2004), but of the species used for experimental melioidosis models, disease (outside of zoological gardens) has only been reported in two rhesus macaques.…”