Presence and shedding of Chlamydia psittaci in waterfowl in a rehabilitation facility and in the wild in New Zealand

ABSTRACT

Aims

To determine the frequency of Chlamydia psittaci infection, shedding dynamics of C. psittaci, and C. psittaci genotype diversity in waterfowl temporarily resident in a rehabilitation facility and in mallards in the wild.

Methods

Conjunctival-choanal-cloacal swabs were collected from apparently healthy captive wild mallards (Anas platyrhynchos; n = 114) and paradise shelducks (Tadorna variegata; n = 10) temporarily housed at a waterfowl breeding and rehabilitation facility (Wellington, NZ) and from wild mallards in Palmerston North (n = 50), and Southland (n = 50). DNA extracted from the swabs was analysed using quantitative PCR (qPCR) high-resolution melt curve (HRM) analysis, targeting the ompA gene of C. psittaci.

Results

Of the captive waterfowl, 39/114 (34%) mallards and 6/10 (60%) paradise shelducks were positive for C. psittaci as were 24/100 (24%) wild mallards. All wild mallards and paradise shelducks carried only C. psittaci genotype C. In captive wild mallards, genotypes A and C, and a mixed infection of both genotypes were found. Captive wild mallards and paradise shelducks were found to be shedding 4 to 5 × 10⁴ and 1 × 10⁵ to 4 × 10⁵ copies of C. psittaci DNA per swab, respectively, with wild mallards shedding 4–677 DNA copies/swab.

Conclusions

Based on qPCR-HRM analysis, a high proportion of wild mallards were infected with C. psittaci but these birds were shedding only a small amount of bacterial DNA. The proportion of sampled ducks that were infected and the extent of bacterial shedding were higher in the birds in a wildlife rehabilitation facility. The major C. psittaci genotype found in the mallards and paradise shelducks was genotype C. This is the first detection of C. psittaci genotype A and co-infection of genotype A and C in ducks.

Clinical relevance

These results indicate that mallards are a reservoir of C. psittaci and therefore may pose a zoonotic risk to people involved in duck hunting, wildlife care and recreational duck feeding. Mallards may also pose a transmission risk to native birds, especially in captive facilities and this has conservation implications for the management of endangered native birds.

KEYWORDS:

• Avian
• chlamydiosis
• psittacosis
• wild bird
• zoonosis

Acknowledgements

This project was funded by the New Zealand Department of Conservation and the Massey University School of Veterinary Science postgraduate fund. The analysis of the expected dissociation temperature of C. psittaci genotype A was done by Priyanka Kulkarni (Massey University, NZ).