In mid-2009 cholera was reported in Papua New Guinea (PNG). Despite low levels of sanitation and hygiene in PNG, there is no evidence of prior outbreaks. In the two years following its introduction over 16,000 cases were reported, with a case fatality rate of 3.2%. The apparent incursion and spread of pathogenic Vibrio cholerae in PNG raises questions about the origin of the pathogen, an issue that has been topical recently in other global locales. We have previously used multi-locus sequence typing and variable number tandem repeat (VNTR) analysis; and most recently genome sequence analysis to better characterise V. cholerae isolates from PNG. Phenotypic and genotypic analyses have confirmed PNG isolates to be altered El Tor, the predominant type currently in global circulation. Genome sequence analysis has demonstrated a close relatedness to Asian strains, supporting our previous VNTR results.
Antimicrobial susceptibility testing of clinical isolates revealed a general lack of resistance. Reduced susceptibility to ampicillin was observed in 50% of isolates tested, but <5% of isolates were resistant to nalidixic acid, gentamicin, streptomycin, cefotaxime or tetracycline. No isolates tested exhibited resistance to multiple antibiotics. Moreover, genome sequence analysis has confirmed the absence of the SXT intergrative-conjugative element (SXT ICE) which commonly harbours multiple resistance genes. Globally, the SXT ICE is common in currently circulating strains of pathogenic V. cholerae, but has been absent in Vietnamese strains in recent years. This may be indicative of shared ancestry between the Vietnamese and PNG strains, but does not confirm direct entry of cholera into PNG from Vietnam. Despite the controversies surrounding efforts to trace V. cholerae origins, it has the potential to guide future public health policy aimed at reducing the global spread of this and other important pathogens.