The effect of human normal serum (HNS) on Pseudomonas pseudomallei was determined. It is apparent from our data that the organism is resistant to the normal serum bactericidal mechanism. Ancillary experiments to confirm this serum-resistant property of P. pseudomallei were done by examining the effects of growth phase conditions of the bacteria (i.e., logarithmic and stationary phases) and different buffered systems used as diluent in our bactericidal assay. Results obtained showed similar degree of resistance to serum bactericidal killing by 5 strains of the organisms tested. The possible survival advantage of serum-resistance property to P. pseudomallei as bacterial pathogens known to invade the blood stream is discussed.
Following the suggestion that it was possible that cases of melioidosis amongst those who had been exposed abroad in the past, might be escaping notice, 487 Royal Marines were examined by indirect haemagglutination studies. Four hundred and eleven of these subjects had served for variable times in areas where melioidosis has been known to occur in Indonesia and Malaya, between 1960 and 1974, occupied in activities in the jungle and paddy fields during which exposure to the disease was to be expected. No evidence of residual subclinical melioidosis was found and it seems unlikely that recrudescent disease will prove to be a problem in the future for English servicemen who have been in South East Asia.
Specific antibody to Pseudomonas pseudomallei exotoxin was detected in sheep sera exposed to natural infection. An enzyme-linked immunosorbent assay (ELISA) was used. Serum antitoxin was present in 49.3% of sera obtained from a flock of sheep naturally exposed to P. pseudomallei infection. Among these sera, 17.0% gave titers of 10,000. In contrast, serum antitoxin was present in only 6.0% of sera collected from sheep kept on a melioidosis-free farm. The ELISA reactivity of all positive sera could be completely absorbed with purified P. pseudomallei exotoxin. Similarly, preincubation of the exotoxin-coated wells with specific antiserum inhibited the ELISA reactivity of sheep sera. The results indicate that exotoxin is produced in vivo during infection by P. pseudomallei.
Titres of melioidosis haemagglutinating antibodies of 1/40 or more were found in 18 of 905 British, Australian, and New Zealand soldiers serving in West Malaysia. Previous mild unsuspected melioidosis seemed to be responsible for these positive titres, which were more common in men exposed to surface water at work and during recreation. This accords with the current view that soil and surface water is the normal habitat of Pseudomonas pseudomallei, the causal organism. Pyrexia of unknown origin after arriving in Malaysia was significantly more common in men with titres of 1/40 or more than in the remainder. It is suggested that mild melioidosis may present as pyrexia of unknown origin. Pyrexias of unknown origin should be investigated vigorously in patients who are in or who have visited endemic areas.
In Malaysia, where vaccination campaigns against foot-and-mouth disease and haemorrhagic septicaemia are routinely carried out, it was desirable to determine whether it was safe and efficacious to administer both vaccines simultaneously. A trial group of 104 cattle was divided into three groups; group 1 animals received both vaccines simultaneously, group 2 animals received only foot-and-mouth disease vaccine and group 3 animals received only haemorrhagic septicaemia vaccine. The serological response to vaccinations was monitored at 0, 21 and 35 days by the virus neutralisation test for foot-and-mouth disease and the mouse-protection and indirect haemagglutination tests for haemorrhagic septicaemia. The simultaneous administration of the two inactivated vaccines produced no adverse effects and the serological response did not differ from the response to either vaccine given separately, thus indicating that cattle may be safely and effectively vaccinated simultaneously in this way.