Contact
Note. From Paungpin et al., (2021), Coinfection of Chlamydia spp. and herpesvirus in juvenile farmed Siamese crocodiles (Crocodylus siamensis) in Thailand, licensed under CC BY 4.0. https://creativecommons.org/licenses/by/4.0/
Crocodylus niloticus
Crocodylus porosus
Crocodylus siamensis
Alligator mississippiensis
(Carossino et al., 2022; Chaiwattanarungruengpais-an et al., 2024; Sariya et al., 2015)
Chlamydiosis in crocodilians is caused by several Chlamydia species, including the recently described Chlamydia crocodile [16]. These species belong to the order Chlamydiales and the family Chlamydiaceae, which comprises Gram-negative, obligate intracellular bacteria [1,14]. As obligate intracellular bacteria, they are highly dependent on their host and cannot survive or replicate independently. Their genomes are very small, approximately 1 million base pairs (Mbp), and they lack the ability to synthesize essential nutrients (e.g., lipids, amino acids, and nucleotides). Additionally, their genomes have evolved to be reduced, removing unnecessary genes while retaining those required for virulence and intracellular survival (i.e., genome streamlining) [9,16].
As seen in obligate intracellular pathogens, these organisms have a specialized two-stage life cycle (biphasic developmental cycle). This cycle involves elementary bodies (EBs, i.e., the infectious form) and reticulate bodies (RBs, i.e., the replicative form) (Figure 3). EBs are approximately 0.2 um in size, metabolically inactive, and found outside of cells. They attach to and infect host cells, and once inside, they differentiate into RBs. RBs are approximately 0.8 µm in size, metabolically active, and rapidly divide by binary fission within the host; however, they are not infectious. Each RB will differentiate back into EBs and be released from the host cell by extrusion or lysis. The cycle continues as EBs go on to infect other cells [1,2].
History
Note. Photo by 2H Media on Unsplash
In the 1990s, high mortality among farmed hatchling crocodiles in South Africa prompted examinations that revealed Chlamydia sp. infection. Additional studies conducted in Zimbabwe on Nile crocodiles (Crocodylus niloticus), which also presented with acute hepatitis, confirmed Chlamydia infection, presumably C. psittaci based on morphology. Although C. psittaci infection in birds is strongly associated with chronic cases of conjunctivitis (i.e., inflammatory eye disease), only a few crocodile cases exhibited conjunctivitis [6].
In 2004, the first case of chlamydiosis within crocodilian species other than Nile crocodiles was detected in farmed saltwater crocodile (Crocodylus porosus) hatchlings and juveniles in Papua New Guinea. The Chlamydia sp. of this outbreak has not been identified. Infected individuals exhibited clinical conditions similar to those in South Africa and Zimbabwe. This case was also linked to the introduction of the disease into wild crocodiles, as infected individuals were initially wild-caught animals purchased [7]. Furthermore, studies conducted in the Northern Territory of Australia from 2005 to 2014 identified 3 new diseases affecting saltwater crocodiles, including chlamydiosis. Co-infection with herpesvirus was also detected, but the Chlamydia sp. remains undetermined [15].
In 2012, the first detection of Chlamydia sp. was found in Siamese crocodiles (Crocodylus siamensis) in Thailand. Later in 2021, an analysis of this causative agent revealed that it was genetically distinct from existing Chlamydia sp. but closely related to C. psittaci and C. caviae. This led to the description of a new Chlamydia sp., C. crocodile [3]. Shortly after, in 2022, an outbreak of chlamydiosis was reported, associated with high mortality among American alligators (Alligator mississippiensis) in Louisiana, United States. Insufficient analysis was performed to determine the infecting Chlamydia sp.; however, it was found to be closely related to C. poikilothermis (predominantly affects snakes) and C. psittaci [2].
Clinical Signs and Progression
Chlamydiosis in crocodilians often results in death due to rapid disease progression. However, some crocodilian species have been reported to be asymptomatic. Initial nonspecific clinical signs include anorexia and lethargy (Figure 1a) [3,17]. Clinical signs highly associated with chlamydiosis include conjunctivitis (i.e., swelling, redness, and accumulation of fibrinocaseous material under the eyelids leading to eye closure) (Figure 1b), pharyngitis (i.e., inflammation of the pharyngeal tissues, which may lead to tissue damage and impaired breathing in severe cases), hepatitis (i.e., inflammation of the liver) (Figure 1c), and kyphoscoliosis (i.e., spinal deformity involving both lateral and dorsal curvature, resulting in a hunched or distorted spine that may impair movement), which is primarily reported in juvenile crocodiles [4,10,16]. Additionally, other clinical signs found in infected reptiles, including some crocodilian species, include pneumonia, myocarditis with necrotizing and granulomatous features, and granulomatous lesions in the small intestine, lung, liver, and spleen [2,14].
Transmission and Epidemiology
Chlamydia sp. can infect humans and a wide range of animals, including chickens, ducks, birds, cattle, sheep, and goats [4]. Reptiles are also susceptible to infection, such as crocodiles, snakes, chameleons, turtles, and tortoises [1]. Transmission between different animals is possible because most Chlamydia species can switch hosts and adapt to diverse environments [5,8,16]. For example, C. pneumoniae, which infects various reptiles, including Nile crocodiles, has been shown to undergo horizontal transmission among zoo animals [8]. Additionally, free-ranging animals, especially birds, can also pose a threat to the spread of disease [17]. The spread of disease within infected animals can also serve as a source of infection for humans, as shown for C. pneumoniae [8]. C. pneumoniae infection in humans is known to cause bronchitis and pneumonia [5]. As mentioned before, chlamydiosis has been detected in Thailand, Australia, Papua New Guinea, and Africa [3,6,7,15]. Additionally, its recent discovery in the United States has raised concerns about its emergence in North America.
Chlamydiosis in crocodilians is primarily transmitted through direct contact with infected individuals, especially via exposure to fecal material and cloacal discharge, which may include material from the gastrointestinal tract. Although not yet confirmed, ocular shedding may contribute to additional routes of infection [2]. Shared water sources may also pose a risk of infection, and the consumption of infected dead livestock represents another potential route of transmission [17]. Although the role of arthropods and other vectors in transmitting this disease has not been established, they have been implicated in transmitting Chlamydia-related bacteria (CRBs). These bacteria are genetically related to Chlamydia, but they do not belong to the same family [18].
Diagnosis
Note. From Chaiwattanarungruengpaisan et al., (2021), A new species of Chlamydia isolated from Siamese crocodiles (Crocodylus siamensis), licensed under CC BY 4.0. https://creativecommons.org/licenses/by/4.0/
Chlamydiosis is diagnosed using nucleic acid amplification (NAA) techniques [12] and microscopic examination of tissues (brain, lung, spleen, and liver). Samples are collected from the conjunctiva, pharynx, and cloaca [2,10]. Molecular testing for Chlamydia sp. includes sequencing of the 16S/23S ribosomal RNA (rRNA) and outer membrane protein A (ompA) genes [4,17]. Microscopic examination of infected cells reveals EBs, RBs, and inclusion bodies (IBs) (Figure 3) [3]. Additionally, immunohistochemical (IHC) techniques are used to identify chlamydial antigens in tissues. Although assays such as enzyme-linked immunosorbent assays (ELISA) and fluorescent antibody tests (FATs) do not differentiate Chlamydia species, they can detect the presence of the organism [1].
Treatment and Prevention
Treatment for chlamydiosis involves the antibiotic oxytetracycline, which has been used since the 1990s [6,11]. However, like most antibiotics, this medication is a primary driver of antimicrobial resistance. Additional concerns arise from the affected animals’ meat quality [11]. Farms that house crocodilians should prioritize preventative care, such as water quality management [16], appropriate handling procedures [5], and strict quarantine of infected individuals. Routinely cleaning should be performed using common disinfectants against Chlamydia sp., including 3% hydrogen peroxide, 70% isopropyl alcohol, 1% Lysol, and benzalkonium chloride [13]. Ultimately, continuous monitoring of this disease is essential for guiding preventative strategies to reduce transmission.
Further Research
Due to the recent discovery of a new Chlamydia sp., much research is needed on this species, such as transmission routes and susceptible hosts [3]. Additionally, the emergence of chlamydiosis in North America warrants further investigation to determine which regions are affected and to identify the Chlamydia sp. involved [2]. Lastly, further research is needed on the antibiotics used, transmission routes, and the role of vectors.
Readings
1. Borel, N., Polkinghorne, A., & Pospischil, A. (2018). A review on chlamydial diseases in animals: still a challenge for pathologists? Veterinary Pathology, 55(3), 374–390. https://doi.org/10.1177/0300985817751218
2. Carossino, M., Nevarez, J. G., Sakaguchi, K., Paulsen, D. B., Langohr, I. M., Strother, K., Ferracone, J., Roy, A., Crossland, N. A., & Del Piero, F. (2022). An outbreak of systemic chlamydiosis in farmed American alligators (Alligator mississippiensis). Veterinary Pathology, 59(5), 860–868. https://doi.org/10.1177/03009858221095269
3. Chaiwattanarungruengpaisan, S., Thongdee, M., Anuntakarun, S., Payungporn, S., Arya, N., Punchukrang, A., Ramasoota, P., Singhakaew, S., Atithep, T., & Sariya, L. (2021). A new species of Chlamydia isolated from Siamese crocodiles (Crocodylus siamensis). PloS one, 16(5), e0252081. https://doi.org/10.1371/journal.pone.0252081
4. Chaiwattanarungruengpaisan, S., Thongdee, M., Arya, N., Paungpin, W., Sirimanapong, W., & Sariya, L. (2024). Diversity and genetic characterization of Chlamydia isolated from Siamese crocodiles (Crocodylus siamensis). Acta Tropica, 253, 107183. https://doi.org/10.1016/j.actatropica.2024.107183
5. Frutos, M. C., Monetti, M. S., Ré, V. E., & Cuffini, C. G. (2014). Molecular evidence of Chlamydophila pneumoniae infection in reptiles in Argentina. Revista Argentina de Microbiología, 46(1), 45–48. https://doi.org/10.1016/S0325-7541(14)70047-1
6. Huchzermeyer, F. W., Gerdes, G. H., Foggin, C. M., Huchzermeyer, K. D., & Limper, L. C. (1994). Hepatitis in farmed hatchling Nile crocodiles (Crocodylus niloticus) due to chlamydial infection. Journal of the South African Veterinary Association, 65(1), 20–22. https://journals.co.za/doi/epdf/10.10520/AJA00382809_1477
7. Huchzermeyer, F. W., Langelet, E., & Putterill, J. F. (2008). An outbreak of chlamydiosis in farmed Indopacific crocodiles (Crocodylus porosus). Journal of the South African Veterinary Association, 79(2), 99–100. https://doi.org/10.4102/jsava.v79i2.253
8. Kabeya, H., Sato, S., & Maruyama, S. (2015). Prevalence and characterization of Chlamydia DNA in zoo animals in Japan. Microbiology and Immunology, 59(9), 507–515. https://doi.org/10.1111/1348-0421.12287
9. Luu, L. D. W., Kasimov, V., Phillips, S., Myers, G. S. A., & Jelocnik, M. (2023). Genome organization and genomics in Chlamydia: whole genome sequencing increases understanding of chlamydial virulence, evolution, and phylogeny. Frontiers in Cellular and Infection Microbiology, 13, 1178736. https://doi.org/10.3389/fcimb.2023.1178736
10. Munson, E., Burbick, C. R., Lawhon, S. D., Krueger, T., & Ruiz-Reyes, E. (2024). Valid and accepted novel bacterial taxa isolated from non-domestic animals and taxonomic revisions published in 2023. Journal of Clinical Microbiology, 62(10), e0104224. https://doi.org/10.1128/jcm.01042-24
11. Nevarez J. G. (2019). Differential diagnoses by clinical signs—crocodilians. Mader's Reptile and Amphibian Medicine and Surgery, 13,1276–1282.e2. https://doi.org/10.1016/B978-0-323-48253-0.00136-7
12. Paungpin, W., Thongdee, M., Chaiwattanarungruengpaisan, S., Sariya, L., Sirimanapong, W., Kasantikul, T., Phonarknguen, R., Darakamas, P., & Arya, N. (2021). Coinfection of Chlamydia spp. and herpesvirus in juvenile farmed Siamese crocodiles (Crocodylus siamensis) in Thailand. Veterinary World, 14(7), 1908–1914. https://doi.org/10.14202/vetworld.2021.1908-1914
13. Ravichandran, K., Anbazhagan, S., Karthik, K., Angappan, M., & Dhayananth, B. (2021). A comprehensive review on avian chlamydiosis: a neglected zoonotic disease. Tropical Animal Health and Production, 53(4), 414. https://doi.org/10.1007/s11250-021-02859-0
14. Sariya, L., Kladmanee, K., Bhusri, B., Thaijongrak, P., Tonchiangsai, K., Chaichoun, K., & Ratanakorn, P. (2015). Molecular evidence for genetic distinctions between Chlamydiaceae detected in Siamese crocodiles (Crocodylus siamensis) and known Chlamydiaceae species. The Japanese Journal of Veterinary Research, 63(1), 5–14. https://www.cabidigitallibrary.org/doi/pdf/10.5555/20153206460
15. Shilton, C. M., Jerrett, I. V., Davis, S., Walsh, S., Benedict, S., Isberg, S. R., Webb, G. J., Manolis, C., Hyndman, T. H., Phalen, D., Brown, G. P., & Melville, L. (2016). Diagnostic investigation of new disease syndromes in farmed Australian saltwater crocodiles (Crocodylus porosus) reveals associations with herpesviral infection. Journal of Veterinary Diagnostic Investigation, 28(3), 279–290. https://doi.org/10.1177/1040638716642268
16. Szymańska-Czerwińska, M., Zaręba-Marchewka, K., & Niemczuk, K. (2023). New insight on chlamydiae. Journal of Veterinary Research, 67(4), 559–565. https://doi.org/10.2478/jvetres-2023-0067
17. Tanpradit, N., Thongdee, M., Sariya, L., Paungpin, W., Chaiwattanarungruengpaisan, S., Sirimanapong, W., Kasantikul, T., Phonarknguen, R., Punchukrang, A., Lekcharoen, P., & Arya, N. (2023). Epidemiology of Chlamydia sp. infection in farmed Siamese crocodiles (Crocodylus siamensis) in Thailand. Acta Veterinaria Scandinavica, 65(1), 50. https://doi.org/10.1186/s13028-023-00713-x
18. Taylor-Brown, A., & Polkinghorne, A. (2017). New and emerging chlamydial infections of creatures great and small. New Microbes and New Infections, 18, 28–33. https://doi.org/10.1016/j.nmni.2017.04.004