Yersiniosis in New Zealand

Abstract

The rate of yersiniosis in New Zealand (NZ) is high compared with other developed countries, and rates have been increasing over recent years. Typically, >99% of human cases in NZ are attributed to Yersinia enterocolitica (YE), although in 2014, a large outbreak of 220 cases was caused by Yersinia pseudotuberculosis. Up until 2012, the most common NZ strain was YE biotype 4. The emergent strain since this time is YE biotype 2/3 serotype O:9. The pathogenic potential of some YE biotypes remains unclear. Most human cases of yersiniosis are considered sporadic without an identifiable source. Key restrictions in previous investigations included insufficient sensitivity for the isolation of Yersinia spp. from foods, although foodborne transmission is the most likely route of infection. In NZ, YE has been isolated from a variety of sick and healthy domestic and farm animals but the pathways from zoonotic reservoir to human remain unproven. Whole-genome sequencing provides unprecedented discriminatory power for typing Yersinia and is now being applied to NZ epidemiological investigations. A "One-Health" approach is necessary to elucidate the routes of transmission of Yersinia and consequently inform targeted interventions for the prevention and management of yersiniosis in NZ.

Keywords: New Zealand; Yersinia; enterocolitica; foodborne; pseudotuberculosis; yersiniosis.

Figure 4

Total number of notified human yersiniosis cases in New Zealand between 2012 and 2019 as recorded in EpiSurv. Distribution of cases per annum (and percentage per year) represented according to Yersinia enterocolitica (YE) biotype (1A, 2/3 and 4) or Yersinia pseudotuberculosis (YP). Rate is calculated as the number of cases per 100,000 population, based on the Statistics New Zealand mid-year population estimates. * Indicates when the first major diagnostic laboratory introduced a culture-independent diagnostic test that included Yersinia enterocolitica (June 2017).

Figure 1

Number of Yersiniosis cases notified in New Zealand by year, 2000–2019, as recorded in EpiSurv. * Value above each data point is the rate per 100,000 population for each year.

Figure 2

Age and sex distribution of yersiniosis cases in New Zealand, 2012–2019 (rate per 100,000 population), as recorded in EpiSurv.

Figure 3

Number of notified yersiniosis cases in New Zealand by month, 2012–2019, as recorded in EpiSurv. * Indicates a peak of notified cases attributed to a large-scale outbreak of Yersinia pseudotuberculosis in 2014.

Figure 5

Microreact visualization of the 164 Yersinia enterocolitica biotype 2/3, O:9 ST12 New Zealand isolates whole-genome sequenced to date. The three isolates shown in the table pertain to a 2016 outbreak. These isolates are also highlighted within the khaki-colored cluster in the phylogenetic tree. The tree is a maximum likelihood tree using core single-nucleotide polymorphic (SNP) differences identified using Snippy 4 [65]. IQ-TREE [68] was used for tree construction with 2000 ultrafast bootstrap [69]. Scale shown within the tree window indicates nucleotide substitutions per site.

Figure 6

Bovine Yersinia notifications in New Zealand (3 week rolling average), 1 January 2011–31 October 2017. Data provided by New Zealand Ministry for Primary Industries.