Cross-species Transmission Potential of Entamoeba histolytica among Humans, Chimpanzees, and Baboons in the Greater Gombe Ecosystem, Tanzania Public

Abstract

Amoebiasis, the diarrheal disease caused by the protozoan Entamoeba histolytica, infects approximately 50 million people worldwide and results in up to 100,000 deaths annually. Amoebiasis is particularly problematic in developing nations where poverty and poor sanitation contribute to the contamination of food and water. Although E. histolytica is a zoonotic parasite that has the potential to infect non-human primates, the potential for such transmission in rural communities that overlap with wild primates remains unknown. Consequently, this study examined the cross-species transmission potential of E. histolytica among humans, chimpanzees, and baboons living in the Greater Gombe Ecosystem, Kigoma District, Tanzania. Risk factors for infection were analyzed using a cross-sectional survey designed for this rural, tropical system that is characterized by high rates of overlap among humans and non-human primates. Five hundred and eighty-seven fecal samples were screened for Entamoeba spp. and E. histolytica. Of the fecal samples examined, 60.3% of human samples, 65.6% of chimpanzee samples, and 88.6% of baboon samples were positive for Entamoeba spp. Further diagnostic PCR revealed E. histolytica infection rates of 12.1% in humans, 34.2% in chimpanzees, and 10.9% in baboons. Chimpanzees had a significantly higher frequency of infection than both humans and baboons. Humans that experienced gastrointestinal symptoms, such as diarrhea and stomach cramps, had greater odds of infection than humans who did not experience gastrointestinal symptoms, when controlling for age and sex (OR = 2.2723; 95% CI 1.0318-5.0043; p = 0.0416). Season, age, and sex were not reliable predictors of E. histolytica infection in humans, chimpanzees, or baboons. The high infection rate of E. histolytica in three sympatric primates - humans, chimpanzees, and baboons - suggests that zoonotic transmission is likely occurring and stresses the need for further phylogenetic studies. Interventions targeting better sanitation and hygiene practices for humans living in and around Gombe National Park can help prevent amoebiasis in humans, while also protecting the endangered chimpanzees and other primates in this region.

Table of Contents

Introduction...........................................................................1

Materials and Methods............................................................4

2.1. Ethics statement...............................................................4

2.2. Study site and sample collection.........................................5

2.3. DNA extraction and molecular detection.............................6

2.4. Human risk factor survey....................................................7

2.5. Statistical analyses and control for sample bias....................7

Results....................................................................................8

Discussion..............................................................................10

References..............................................................................13

Tables....................................................................................16

Table 1. List of primers used in PCR for detection of Entamoeba spp.

and E. histolytica in humans and non-human primates in and

around Gombe National Park, Tanzania....................................16

Table 2. Detection of Entamoeba spp. and E. histolytica in three

primate species samples in and around Gombe National

Park, Tanzania........................................................................17

Table 3. Infection rate of E. histolytica detected by location in and

around Gombe National Park, Tanzania...................................18

Table 4. Risk factors for E. histolytica infection in humans living in

and around Gombe National Park, Tanzania.............................19

Table 5. Risk factors for E. histolytica infection in chimpanzees in

Gombe National Park, Tanzania...............................................20

Table 6. Risk factors for E. histolytica infection in baboons in Gombe

National Park, Tanzania..........................................................21

Figures...................................................................................22

Figure 1. Life cycle of Entamoeba histolytica.............................22

Figure 2. Chimpanzee communities located in Gombe National

Park, Tanzania.......................................................................23

About this Master's Thesis

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School	Rollins School of Public Health
Department	Environmental Health
Degree	MPH
Submission	Master's Thesis
Language	English
Research Field	Health Sciences, Public Health Biology, Ecology Health Sciences, Epidemiology
Mot-clé	Amoebiasis Gombe National Park Entamoeba histolytica Parasite Zoonosis
Committee Chair / Thesis Advisor	Gillespie, Thomas R., Emory University
Committee Members	Tolbert, Paige, Emory University

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