Endamoeba coli: Dose Response Models

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Endamoeba coli

Author: Sushil Tamrakar
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If you want to download the excel spreadsheet of tables, please click the captions of tables. If you want to download a specific figure, just click on the figure

Overview of Endamoeba coli

Amoebiasis is defined as infection with the protozoan parasite Entamoeba histolytica. However there are several Endamebas species which are closely related to E. histolytica such as E. dipar and E. coli. (Anonymous 1997)

Entamoeba coliare a non-pathogenic species of Entamoeba that frequently exists as a commensal parasite in large intestine of the human. Both cysts and trophozoites of the species are passed in stool and considered diagnostic (CDC 2009). Cysts are typically found in formed stool, whereas trophozoites are typically found in diarrheal stool.  Colonization of the nonpathogenic amebae occurs after ingestion of mature cysts in fecally-contaminated food, water, or fomites(CDC 2009).

Summary of data

Rendtorff, R. C. (1954). "The Experimental Transmission of Human Intestinal Prozoan Parasites.I. Endamoeba coli Cyst Given in Capasules." American Journal of Hygien 59: 196-208- studied the Entamoeba coli exposure to human volunteers (Rendtorff 1954). Known numbers of cysts of E. coli were administered orally in capsules to volunteers to determine numbers of parasites necessary to establish the infection

Table 1. Summary of data for Entamoeba coli
Experiment Number Reference Host Type/Pathogen Strain Route/# of Doses Dose Units Response Best Fit Model Optimized Parameter(s) ID50
1 (Rendtorff 1954) Humans Ingestion – 5 No. of cysts Infection Beta-Poisson α = 0.10
N50 = 340.78

Optimized Models and Fitting Analyses

Optimization Output for experiment 1

Table 2. Humans model data
Dose Infected Not infected Total
10000 2 0 2
1000 0 2 2
100 2 2 4
10 3 7 10
1 1 7 8
Rendtorff 1954

Table 3. Goodness of Fit and Model Selection
Model Deviance Δ Degrees
of Freedom
Exponential 27.82 22.78 4 3.84
Beta Poisson 5.04 3 7.81
Beta Poisson is best fitting model
Table 4 Optimized parameters for the best fitting (beta Poisson), obtained from 10,000 bootstrap iterations
Parameter MLE Estimate Percentiles
0.5% 2.5% 5% 95% 97.5% 99.5%
α 0.10 -- -- -- -- -- --
N50 340.78 -- -- -- -- -- --
LD50 340.78 5.91 17.33 29.94 147504.7 2081588 1.19E+10

Figure 1 Parameter scatter plot for beta Poisson model ellipses signify the 0.9, 0.95 and 0.99 confidence of the parameters
Figure 2 Beta-Poisson model plot, with confidence bounds around optimized model


Anonymous (1997). "Entamoeba taxonomy." Bulletin of the World Health Organization 75(3): 291-292.

CDC (2009). Intestinal Amebae. D. o. P. Diseases.

Rendtorff, R. C. (1954). "The Experimental Transmission of Human Intestinal Prozoan Parasites. I. Endamoeba coli Cyst Given in Capasules." American Journal of Hygien 59: 196-208.