Epidemiology of Chlamydia sp. infection in farmed Siamese crocodiles (Crocodylus siamensis) in Thailand

Abstract

Background: Although Chlamydia sp. causes widespread disease outbreaks in juvenile crocodiles in Thailand, data regarding the epidemiology, and risk factors of such infections are limited. The aim of this study was to investigate the prevalence and possible risk factors associated with Chlamydia sp. infections on Siamese crocodile (Crocodylus siamensis) farms in Thailand. A cross-sectional study was conducted from July to December 2019. Samples were collected from 40 farms across six regions in Thailand. Conjunctival, pharyngeal, and cloacal swab samples were analyzed for Chlamydiaceae nucleic acids using semi-nested PCR followed by phylogenetic analysis based on the ompA gene fragment. Risk factors of infection were analyzed using chi-square and univariate regression to calculate odds ratios.

Results: The prevalence of Chlamydia sp. infection across all regions was 65%. The ompA phylogenetic analysis showed that Chlamydia sp. detected in this study was genetically closely related to Chlamydia crocodili and Chlamydia caviae. The risk factors for infection were water source, reusing treated wastewater from the treatment pond, not disposing of leftover food, low frequency of water replacement in the enclosure of juvenile crocodiles, and lack of water replacement after the death of a crocodile.

Conclusion: The prevalence of Chlamydia sp. infection in farmed crocodiles in Thailand was 65% during the study period. Cloacal swabs were superior to conjunctival and pharyngeal swabs due to their higher sensitivity in detecting Chlamydia sp., as well as their lower invasiveness. Good management and biosecurity in crocodile farming can reduce the risk of Chlamydia sp.

Keywords: Chlamydiosis; OmpA; Polymerase chain reaction; Risk factors.

Fig. 1

Provinces in Thailand with PCR results positive for Chlamydia sp. See Additional Table S1 for the numbers of farms and crocodiles tested for each province. 1: Lamphun, 2: Lampang, 3: Kalasin, 4: Mahasarakham, 5: Roi Et, 6: Nakhon Sawan, 7: Uthaithani, 8: Kanchanaburi, 9: Chainat, 10: Lopburi, 11: Nakhon Ratchasima, 12: Suphanburi, 13: Singburi, 14: Phra Nakhon Si Ayutthaya, 15: Saraburi, 16: Nakhon Nayok, 17: Prachinburi, 18: Chachoengsao, 19: Chonburi, 20: Petchaburi, 21: Trang, 22: Satun, and 23: Songkhla

Fig. 2

The ompA phylogenetic tree. A total of 992 bp nucleotide sequence was used for phylogenetic construction using MEGA11. Numbers show the percentage of times each branch was found in 1000 bootstrap replicates. The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The black circle indicates the samples obtained in this study