Acanthamoeba Keratitis
Author: Sushil Tamrakar
General overview of Acanthamoeba Keratitis
Acanthamoeba keratitis is a rare but serious infection of the eye that can result in permanent visual damage or even causes blindness. This infection is caused by freeliving amoeba Acanthamoeba. Acanthamoeba causes the disease when it infects the cornea. Acanthamoebae are very common in nature and can be found in water and soil ^{[1]}.
Summary Data
Badenoch et al (1990) experimented with Acanthamoeba and Corynabacteruim in rats to study the effect of pathogens in the cornea. In that study, the authors inoculated Acanthamoeba (Ac 118) and Corynebacterium organisms into rat corneas. No effect was observed for groups of rats dosed with graded doses of Acanthamoeba alone, while in combination with Corynebacterium, there were some responses at higher doses.
Experiment serial number 
Reference 
Host type 
Agent strain 
Route 
# of doses 
Dose units 
Response 
Best fit model 
Optimized parameter(s) 
LD_{50}/ID_{50}

264 
^{[2]} 
rat 
Ac118 
eyes cornea 
4 
no of trophozoites 
infection 
exponential 
k = 1.01E04 
6.89E+03

265 
^{[2]} 
rat 
Ac119 
eyes cornea 
4 
no of trophozoites 
infection 
exponential 
k = 3.63E04 
1.91E+03

*This model is preferred in most circumstances. However, consider all available models to decide which one is most appropriate for your analysis.


Optimization Output for experiment 264
Dose response data ^{[2]}
Dose 
Infected 
Noninfected 
Total

10 
0 
8 
8

100 
0 
16 
16

1000 
2 
16 
18

1E+04 
5 
3 
8


Goodness of fit and model selection
Model 
Deviance 
Δ 
Degrees of freedom 
χ^{2}_{0.95,1} pvalue 
χ^{2}_{0.95,mk} pvalue

Exponential

0.388

0.00767

3

3.84 0.93

7.81 0.943

Beta Poisson

0.381

2

5.99 0.827

Exponential is preferred to betaPoisson; cannot reject good fit for exponential.


Optimized k parameter for the exponential model, from 10000 bootstrap iterations
Parameter

MLE estimate

Percentiles

0.5% 
2.5% 
5% 
95% 
97.5% 
99.5%

k 
1.01E04 
2.24E05 
3.58E05 
4.82E05 
1.90E04 
2.16E04 
2.59E04

ID50/LD50/ETC* 
6.89E+03 
2.68E+03 
3.21E+03 
3.65E+03 
1.44E+04 
1.94E+04 
3.10E+04

*Not a parameter of the exponential model; however, it facilitates comparison with other models.


Parameter histogram for Exponential model (uncertainty of the parameter) Exponential model plot, with confidence bounds around optimized model
Optimization Output for experiment 265
Dose response data ^{[2]}
Dose 
Infected 
Noninfected 
Total

10 
0 
8 
8

100 
0 
16 
16

1000 
7 
17 
24

1E+04 
10 
0 
10


Goodness of fit and model selection
Model 
Deviance 
Δ 
Degrees of freedom 
χ^{2}_{0.95,1} pvalue 
χ^{2}_{0.95,mk} pvalue

Exponential

1.78

0.000219

3

3.84 1

7.81 0.62

Beta Poisson

1.78

2

5.99 0.411

Exponential is preferred to betaPoisson; cannot reject good fit for exponential.


Optimized k parameter for the exponential model, from 10000 bootstrap iterations
Parameter

MLE estimate

Percentiles

0.5% 
2.5% 
5% 
95% 
97.5% 
99.5%

k 
3.63E04 
2.04E04 
2.30E04 
2.59E04 
5.69E04 
5.69E04 
7.09E04

ID50/LD50/ETC* 
1.91E+03 
9.78E+02 
1.22E+03 
1.22E+03 
2.68E+03 
3.01E+03 
3.39E+03

*Not a parameter of the exponential model; however, it facilitates comparison with other models.


Parameter histogram for exponential model (uncertainty of the parameter) Exponential model plot, with confidence bounds around optimized model
Summary
There was no effect of Acanthamoeba without Corynebacterium.
References
 ↑ CDC. (2012). "Parasites Acanthamoeba." Retrieved 03/30/2012, 2012, from http://www.cdc.gov/parasites/acanthamoeba/.
 ↑ ^{2.0} ^{2.1} ^{2.2} ^{2.3} Badenoch, P. R., A. M. Johnson, et al. (1990). "Pathogenicity of Acanthamoeba and Corynebacterium in the Rat Cornea." Archives of Ophthalmology 108: 107112.