Endamoeba coli: Dose Response Models

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Endamoeba coli

Author: Sushil Tamrakar

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. [1]

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 [2]. 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 [2].

Summary of data

Rendtorff, R. C. (1954) studied the Entamoeba coli exposure to human volunteers with a known numbers of cysts of E. coli were administered orally in capsules to volunteers to determine numbers of parasites necessary to establish the infection.

Experiment serial number Reference Host type Agent strain Route # of doses Dose units Response Best fit model Optimized parameter(s) LD50/ID50
45* [3] human From an infected human oral 5 Cysts infection beta-Poisson α = 1.01E-01 , N50 = 3.41E+02 3.41E+02
*This model is preferred in most circumstances. However, consider all available models to decide which one is most appropriate for your analysis.
Exponential and betapoisson model.jpg

Optimization Output for experiment 45

Humans model data [3]
Dose Infected Non-infected Total
1 1 7 8
10 3 7 10
100 2 2 4
1000 0 2 2
1E+04 2 0 2

Goodness of fit and model selection
Model Deviance Δ Degrees
of freedom
Exponential 27.8 22.8 4 3.84
Beta Poisson 5.04 3 7.81
Beta-Poisson fits better than exponential; cannot reject good fit for beta-Poisson.

Optimized parameters for the beta-Poisson model, from 10000 bootstrap iterations
Parameter MLE estimate Percentiles
0.5% 2.5% 5% 95% 97.5% 99.5%
α 1.01E-01 1.20E-03 2.60E-02 3.61E-02 2.12E-01 2.57E-01 3.08E-01
N50 3.41E+02 5.02E+00 1.73E+01 2.61E+01 1.48E+05 2.08E+06 1.19E+10

Parameter scatter plot for beta Poisson model ellipses signify the 0.9, 0.95 and 0.99 confidence of the parameters.
beta Poisson model plot, with confidence bounds around optimized model


  1. Anonymous (1997). Entamoeba taxonomy. Bulletin of the World Health Organization 75.3: 291-292.Full text
  2. 2.0 2.1 CDC
  3. 3.0 3.1 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.