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Volume 29, Number 4—April 2023
Rickettsia conorii Subspecies israelensis in Captive Baboons
Hamadryas baboons (Papio hamadryas) may transmit zoonotic vector-borne pathogens to visitors and workers frequenting zoological parks. We molecularly screened 33 baboons for vector-borne pathogens. Three (9.1%) of 33 animals tested positive for Rickettsia conorii subspecies israelensis. Clinicians should be aware of potential health risks from spatial overlapping between baboons and humans.
Papio hamadryas baboons (order Primates, family Cercopithecidae) are frequently hosted in zoological gardens worldwide. The natural susceptibility of baboons to many zoonotic agents (1) may present a potential risk for transmission of emerging infectious diseases to humans. Nevertheless, few data are available on vector-borne pathogens of human concern that are hosted by baboons (e.g., Rickettsia africae, Babesia microti–like parasites, and Anaplasma phagocytophilum) (1). Data are likewise scarce on the role of P. hamadryas baboons in circulating arthropod vectors in zoological gardens and the resulting risk for transmitting vector-borne pathogens to persons frequenting such areas. We aimed to determine the occurrence of zoonotic vector-borne pathogens in a zoopark in the Apulia region of southern Italy and assess baboons’ potential roles as reservoirs of emerging pathogens. Our study was approved by the University of Bari Aldo Moro ethics committee (Prot. Uniba 176/19).
During February–December 2020, we anesthetized baboons in the zoopark and housed them in cages for blood sampling. For each baboon, we recorded age, sex, weight, and body condition score (1–5); we obtained peripheral blood samples by cephalic vein puncture. To determine complete blood count and for molecular analysis, we collected 2 mL blood samples in Vacutainer K3-EDTA tubes. For biochemical analysis, we collected an additional 5 mL blood in Vacutainer clot activator serum tubes and centrifuged (15 min at 1,500 × g at room temperature), then delivered it to the University of Bari Department of Veterinary Medicine (Bari, Italy). We extracted DNA using QIAGEN QIAamp DNA Blood and Tissue kits (https://www.qiagen.com) and molecularly tested for vector-borne pathogens (Table) (2–4). We purified and sequenced amplicons in both directions using a Big Dye Terminator v3.1 Cycle Sequencing Kit in an Applied Biosystems 3130 Genetic Analyzer (ThermoFisher, https://www.thermofisher.com), then edited and analyzed them using Geneious version 9.0 (https://www.geneious.com). We then compared resulting sequences with those in GenBank. We performed complete blood counts using CELL-DYN 3700 Hematology Analyzer (Abbott, https://www.abbott.com), biochemical profile using a KPM Analytics SAT 450 random access analyzer (https://www.kpmanalytics.com), and protein electrophoresis analyses using Sebia Hydrasys 2 Scan Focusing (, https://www.sebia.com). We calculated 95% CIs for proportions and χ2 and odds ratios (OR) to assess differences in prevalence and infection risk stratified by age and sex. We used t-tests to compare mean laboratory values between baboons positive and negative for vector-borne pathogens. We considered p values <0.05 statistically significant.
We included 33 baboons: 21 male, 12 female; 13 juvenile, 16 adult, and 4 elderly. Blood samples from 3/33 (9.1%, 95% CI 3.1%–23.4%; 1 adult male, 1 adult female, 1 juvenile male) were positive for R. conorii subsp. israelensis by the gltA gene; all samples were negative by ompA and ompB genes. The only sequence type we identified showed 99%–100% nucleotide identity with R. conorii subsp. israelensis from GenBank; we deposited our sequence in GenBank (accession no. OQ360110). All baboons tested negative for other vector-borne pathogens.
Although we found adult and male baboons at higher risk for infection (OR 2.6), we found no significant difference by age or sex (p = 0.439). No baboon showed ectoparasitic infestation or clinical signs of vector-borne diseases, and all displayed good physical status (mean complete blood count 3, average bodyweight 17.5 kg). Hematologic and serum chemistry values were within normal ranges (Appendix Tables 1, 2) for both R. conorii–negative and –positive baboons (p >0.05).
Our study revealed a nonnegligible prevalence (9.1%, 3/33) of R. conorii subsp. israelensis in P. hamadryas baboons, representing a pathogen–host association previously demonstrated only among asymptomatic dogs and cats from Portugal (5) and in severe cases among symptomatic humans from Italy (6). This survey confirms circulation of rickettsiae among baboons, also reported in 1 study of R. africae in P. cynocephalus yellow baboons from Zambia (1).
Despite routine treatment of baboons (orally administering 0.4 mg/kg ivermectin every 15 days by ground bait), presence of ticks in the zoopark was supported by a previous finding of tickborne pathogens (A. phagocytophilum, Coxiella burnetii, and Rickettsia spp.) in a lion (7). Given the baboon grooming behavior of removing ectoparasites from their bodies, lack of Rhipicephalus sanguineus sensu lato ticks, a vector of rickettsiae (8), was not surprising (9). However, association between zoopark-dwelling baboons and Rhipicephalus spp. ticks, including R. sanguineus s.l., is well known (9). Because this tick species is prevalent in the study area in all developmental stages, exposure very likely occurs (10).
Taken together, the high density of P. hamadryas baboons, their close proximity to the zoopark, and the anthropophilic behavior of R. sanguineus s.l. ticks (10) highlight the threat to park visitors and workers from R. conorii subsp. israelensis infection. Absence of clinical signs in positive baboons and lack of differences in hematological and biochemical parameters between negative and positive animals indicate the asymptomatic features of infection and make clarifying the baboons’ role as a potential reservoir more urgent. Measures to control tick circulation should be established to reduce risk for transmission of R. conorii subsp. israelensis to zoopark visitors and workers.
Mr. Sgroi has a PhD in animal health and zoonosis from the University of Bari Aldo Moro. His main research activities focus on biology, epidemiology, and control of vector-borne pathogens of zoonotic concern.
The authors are grateful to the staff of Fasano Zoopark involved in field activities.
R.I. and D.O. were partially supported by EU funding within the NextGeneration EU-MUR PNRR Extended Partnership initiative on Emerging Infectious Diseases (Project no. PE00000007, INF-ACT).
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TableCite This Article
Original Publication Date: March 17, 2023
Table of Contents – Volume 29, Number 4—April 2023
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Domenico Otranto, University of Bari Aldo Moro, strada provinciale per Casamassima km3, 70010 Valenzano, Italy