Abstract
Studies examining the prevalence of zoonotic agents in the Caribbean are very limited. The objective of this study was to examine the seroprevalence of seven zoonotic agents among individuals residing on 10 English-speaking Caribbean countries. Sera from healthy, pregnant women were collected from Antigua-Barbuda, Belize, Bermuda, Dominica, Grenada, Jamaica, Montserrat, St. Kitts-Nevis, St. Lucia, and St. Vincent-Grenadines and tested for the presence of IgG antibodies to dengue virus, hepatitis E virus, hantaviruses, leptospiral agents, spotted fever group rickettsiae (SFGR), typhus group rickettsiae (TGR), and Coxiella burnetii (Q fever). The highest seroprevalence values were observed for dengue virus, SFGR, and leptospirosis, although the lowest seroprevalence values were observed for hepatitis E virus, C. burnetii, and TGR. Antibodies to hantaviruses were not detected in any individuals.
Introduction
The epidemiology of zoonotic infections within the Caribbean region is currently poorly understood. A limited number of studies have focused on zoonotic pathogens of humans and livestock and include a review of tick-borne transmission of rickettsial agents and studies on Rickettsia africae in livestock on eight Caribbean islands.1,2 Other studies have identified dengue virus (a mosquito-borne arbovirus) and leptospirosis as emerging health problems.3–6 Limited cases of zoonotic hepatitis E virus (HEV) infection have been documented but only preliminary characterization has been performed.7 The objective of this study was to examine the seroprevalence of seven zoonotic agents among individuals residing in 10 Caribbean countries.
Methods
From 2009 to 2011, blood samples were collected from up to 50 healthy, pregnant women from the following countries: Antigua-Barbuda, Belize, Bermuda, Dominica, Grenada, Jamaica, Montserrat, St. Kitts-Nevis, St. Lucia, and St. Vincent-Grenadines.8 This study was approved by the ethics committees of St. George's University, Grenada and the University of Laval, Quebec, Canada. Informed consent was obtained from all participants. All samples were processed at Ross University School of Veterinary Medicine (RUSVM) in St. Kitts. A total of 442 serum samples were tested for antibodies against HEV and leptospiral agents at RUSVM; and for antibodies against dengue virus, hantaviruses, spotted fever group rickettsiae (SFGR), typhus group rickettsiae (TGR), and Coxiella burnetii at the National Microbiology Laboratory in Canada. Sera were tested for immunoglobulin G (IgG) antibodies using the following kits: Dengue IgG ELISA (Focus Diagnostics, Cypress, CA), Hantavirus IgG DxSelect kit (Focus Diagnostics), recombLine HantaPlus IgG kit (Phoenix AirMid Biomedical, Ontario, Canada), Hepatitis E Virus (HEV) ELISA (MP Biomedicals, Asia Pacific Ltd.), Leptospira biflexa (serovar patoc 1) Microwell IgG ELISA (Diagnostic Automation, Inc., Calabasas, California), Panbio Coxiella burnetii (Q fever) IgG ELISA (Alere Inc., Ottawa, Ontario), and Q fever IFA IgG (Focus Diagnostics). All assays were performed according to the manufacturers' instructions.
Serum samples were tested for IgG antibodies against SFGR using an in-house indirect immunofluorescent antibody (IFA) with R. rickettsii antigen and to TGR using R. typhi antigen.9 Serum samples were screened for IgG antibodies to hantaviruses using the Hantavirus IgG DxSelect kit. Samples that tested positive or equivocal on the commercial enzyme-linked immunosorbent assay (ELISA) were then tested with an in-house ELISA (using Black Creek Canal virus as antigen) and the recombLine HantaPlus IgG kit to confirm the results of the DxSelect kit.10 Serum samples were screened for IgG antibodies to phase II C. burnetii using the Panbio ELISA kit. Samples that tested positive or equivocal by ELISA were then tested with the Focus Diagnostics IFA kit to confirm the ELISA results and to determine the end-point titers for IgG against phase I and II C. burnetii antigens.
Results
The majority of individuals enrolled in this study were positive for IgG antibodies to dengue virus, with an overall seroprevalence of 83.0 ± 3.5% Table 1. Seroprevalence values of 80–100% were observed for all countries except Bermuda (8%) and Belize (36%). This suggests that the risk for dengue exposure in these countries may be lower than in the others studied. Because of the cross-reactive nature of flavivirus antibodies, it is possible that a portion of the dengue seropositive specimens may be associated with exposure to other flaviviruses. However, the results from this study are consistent with previous studies indicating extensive circulation of dengue virus serotypes throughout the Caribbean.6
Table 1.
Seroprevalence of zoonotic pathogens in pregnant women from 10 Caribbean Islands*
| Country | Zoonotic pathogen seroprevalence ± 95% CI | ||||||
|---|---|---|---|---|---|---|---|
| Dengue virus | Hantaviruses | Hepatitis E virus | Leptospira species | SFGR | TGR | C. burnetii | |
| Antigua-Barbuda | 94.7 ± 7.1 | ND | ND | 10.5 ± 9.8 | 36.8 ± 15.3 | ND | 5.3 ± 6.6 |
| Belize | 36.0 ± 13.3 | ND | ND | 8.0 ± 7.5 | 54.0 ± 13.8 | ND | ND |
| Bermuda | 8.0 ± 7.5 | ND | ND | 12.0 ± 9.0 | 40.0 ± 13.6 | ND | ND |
| Dominica | 98.0 ± 3.9 | ND | ND | 16.0 ± 10.2 | 36.0 ± 13.3 | 2.0 ± 3.9 | ND |
| Grenada | 98.0 ± 3.9 | ND | 2.0 ± 3.8 | 21.6 ± 11.3 | 2.0 ± 3.9 | 2.0 ± 3.8 | ND |
| Jamaica | 100.0 ± 0.0 | ND | 2.1 ± 4.1 | 42.6 ± 14.1 | 44.7 ± 14.2 | 2.1 ± 4.1 | 2.1 ± 4.1 |
| Montserrat | 80.0 ± 20.2 | ND | ND | 20.0 ± 20.2 | 20.0 ± 20.2 | ND | 6.6 ± 12.7 |
| St. Kitts-Nevis | 100.0 ± 0.0 | ND | ND | 9.1 ± 8.5 | 43.2 ± 14.2 | 2.3 ± 4.3 | 13.6 ± 10.1 |
| St. Lucia | 97.0 ± 4.1 | ND | 2.2 ± 4.2 | 19.6 ± 11.5 | 14.9 ± 10.2 | 2.1 ± 4.1 | ND |
| St. Vincent-Grenadines | 94.0 ± 6.6 | ND | 2.0 ± 3.9 | 26.0 ± 12.2 | 36.0 ± 13.3 | 4.2 ± 5.4 | ND |
| All countries | 83.0 ± 3.5 | ND | 1.4 ± 1.1 | 18.6 ± 3.6 | 33.5 ± 4.4 | 1.6 ± 1.2 | 2.3 ± 1.4 |
CI = confidence interval; ND = not detected.
A high seroprevalence to SFGR was detected throughout the countries studied. Overall, 33.5 ± 4.4% of the samples displayed a titer of ≥ 64 when Rickettsia rickettsii was used as the antigen. All samples reactive at a titer of ≥ 64 to SFGR were non-reactive against R. typhi antigen, indicating that the serological response was specific to SFGR. In contrast to SFGR, a very low seroprevalence of 1.6 ± 1.2% for TGR was detected. However, the seroprevalence of leptospirosis was 18.6 ± 3.6% overall, with seropositive individuals detected in all countries studied, suggesting ongoing circulation of Leptospira species throughout the region. The seroprevalences of HEV (1.4 ± 1.1%) and C. burnetii (2.3 ± 1.4%) were low and no individuals were seropositive for hantaviruses.
Discussion
This is the first study to examine the seroprevalence of a variety of bacterial and viral zoonotic agents in inhabitants of 10 Caribbean countries. Overall, the highest seroprevalence values were documented for dengue viruses, SFGR, and leptospiral agents, whereas lower values were shown for HEV, TGR, and Q fever, and no individuals were found seropositive for exposure to hantaviruses (Table 1).
Dengue virus is one of the world's most important mosquito-borne viruses and the Caribbean region has experienced a major surge in activity.4–6,11,12 Dengue virus can circulate in sylvatic cycles involving non-human primates and can therefore be considered zoonotic; however, most transmission occurs in urban cycles involving only humans and mosquitoes. Nevertheless, the importance of this virus as a major vector-borne pathogen justified its inclusion in this study and the high degree of seroprevalence observed is consistent with previous studies showing the hyperendemic nature of its circulation in the Caribbean. The results from this study agree with a recent publication on the prevalence of dengue virus antibody in healthy Jamaicans in which 100% of participants were seropositive.13
Leptospirosis is an emerging bacterial zoonosis that has a greater incidence in tropical areas where conditions for transmission are favorable and many wild and domestic animals serve as reservoirs.14 Transmission to humans is usually by contact with water contaminated by animal urine and dengue-like febrile illness may result from infection. The results described here are consistent with recent studies that indicate that suspect dengue cases may actually be associated with Leptospira infection and exposure rates may be higher in the Caribbean than previously believed.3
Coxiella burnetii is endemic worldwide and is transmitted to humans usually by contamination of the environment with the birth products from infected sheep, goats, or cattle. Acute Q fever typically presents as a flu-like illness with fever and headache, and some patients may present with pneumonia or hepatitis.15 In this study, the overall seroprevalence was determined to be 2.3% among women living in the Caribbean, using a cutoff of ≥ 64 for the determination of seropositivity. Interestingly, our results are consistent with the seroprevalence of Q fever in the United States, which was determined to be 3.1% among healthy adults, although the seroprevalence was higher in men (3.8%) than women (2.5%).16
Previous studies have shown that R. africae-infected Amblyomma variegatum ticks are widespread in the Caribbean. However, only one human serosurvey has been published involving individuals from the Caribbean.17 In a study conducted in Guadeloupe, 49% of individuals tested had antibody titers of ≥ 50 to R. africae, and the prevalence in men was significantly higher than in women (66% in men versus 39% in women at a titer of ≥ 50). Seroprevalence values among women in both the serosurvey from Guadeloupe and this study are consistent (39% versus 33.5%, respectively), suggesting a high rate of exposure to infected tick vectors within the Caribbean region. These results are also consistent with other studies that have found a high prevalence of R. africae in Amblyomma variegatum ticks in several Caribbean countries, such as Guadeloupe, St. Kitts-Nevis, Dominica, Montserrat, St. Lucia, and Antigua, with infection rates ranging from 7% to over 50% of all A. variegatum ticks tested.1,17–19
A low seroprevalence rate (1.6%) was observed for typhus group rickettsiae, suggesting that these are not common infections in the Caribbean. R. typhi is the etiological agent of murine typhus, and is typically transmitted to humans via rat fleas with rodents serving as the primary reservoir.20 Although considered endemic worldwide, and prevalent in the coastal areas of tropical and subtropical regions, the results from this study suggest that R. typhi is not a common zoonotic agent in the countries included in this study.
Hepatitis E is endemic in regions of poor sanitation and has been chiefly associated with cases in Africa, Asia, the Mediterranean, Mexico and South America.21 Several Caribbean countries have reported HEV circulation, but viral characterization has been limited.7 Although the transmission of the virus is primarily fecal–oral through contaminated water, there is also evidence of zoonotic transmission in certain cases. Recent studies have investigated swine, including pork meat, as a source of zoonotic hepatitis E infection.22 The results from this study indicate a low prevalence of antibody in the individuals tested (although the possibility that these results may represent false-positives cannot be ruled out); however, the possible route(s) of transmission of this virus requires further study.
Hantaviruses are rodent-borne and contribute to significant numbers of cases associated with hemorrhagic fever and pulmonary syndromes.23,24 Antibodies to hantaviruses were not detected in any of the samples analyzed in this study; this is in contrast to a recent study that showed significant exposure rates among farm and abattoir workers in Trinidad.25 Further investigations to evaluate the risk for hantavirus infection in the Caribbean are thus warranted.
Footnotes
Authors' addresses: Heidi Wood, Michael A. Drebot, Liz Dillon, Kristina Dimitrova, Allen Grolla, and Kai Makowski, Public Health Agency of Canada, Winnipeg, Manitoba, Canada, E-mails: Heidi.Wood@phac-aspc.gc.ca, Mike.Drebot@phac-aspc.gc.ca, Liz.Dillon@phac-aspc.gc.ca, Kristina.Dimitrova@phac-aspc.gc.ca, Allen.Grolla@phac-aspc.gc.ca, and Kai.Makowski@phac-aspc.gc.ca. Eric Dewailly, Laval University, Quebec City, Quebec, Canada, E-mail: Eric.Dewailly@crchul.ulaval.ca. Martin Forde, St. George's University, St. George's, Grenada, E-mail: martinforde@gmail.com. Elise Lee, University of Florida, Gainesville, FL, E-mail: elise575@gmail.com. Amanda Loftis, Ross University School of Veterinary Medicine, St. Kitts, E-mail: adloftis@gmail.com. Karen Morrison, York University, Toronto, Ontario, Canada, E-mail: kmorriso@yorku.ca. Lyndon Robertson, Caribbean EcoHealth Programme (CEHP), Windward Islands Research and Education Foundation (WINDREF), St. George's, Grenada, E-mail: forbes.robertson@gmail.com. Rosina C. Krecek, Texas A&M University, College Station, TX, and University of Johannesburg, Auckland Park, South Africa, E-mail: tkrecek@cvm.tamu.edu.
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