Evaluation of three different methods to establish animal models of Acanthamoeba keratitis

Abstract

Purpose: To produce animal models of Acanthamoeba keratitis and to evaluate the advantages and adaptation range of each of the three methods employed.

Materials and methods: Mice and Wistar rats in three groups of 15 rats and 15 mice each were used to establish the models. Right corneas in group A were scratched and challenged with Acanthamoeba. Those in group B were scratched and covered with contact lenses incubated with Acanthamoeba. Those in group C received an intrastromal injection of Acanthamoeba. Five rats and 5 mice in each group were used for histopathological investigations and the other 10 in each group were used for clinical evaluation. The models were evaluated by slit lamp examination, microscopic examination and culture of corneal scrapings, HE staining of corneal sections, and pathological scoring of the infections.

Results: Four rats and 6 mice in group A, 7 rats and 8 mice in group B, and 10 rats and 10 mice in group C developed typical Acanthamoeba keratitis.

Conclusion: Corneal scratching alone has the lowest infection rate, while scratching and then covering with contaminated contact lenses has a moderate rate of infection and most closely mimics what happens in most human infections. Intrastromal injection of Acanthamoeba gives a much higher infection rate and more severe Acanthamoeba keratitis.

Keywords: Acanthamoeba; animal model; corneal infection; keratitis.

Fig. 1

Typical cysts were observed on 10% potassium hydroxide wet mount of corneal scraping tissues (Original magnificence:×200).

Fig. 2

HE staining of corneal sections of rats from Group C. Acanthamoeba cysts in the corneal sections is indicated by red arrow. They are surrounded by infiltrated leukocytes and corneal stroma edema (Original magnificence:×400).

Fig. 3

Clinical manifestations of AK in rats of all three groups. The pictures in "0d" are the slit lamp photos of the eyes in normal rats. On the 3rd day after inoculation, obvious infections developed in all three groups and on the 6th day, typical ring ulcer was observed in group C. On the 10th day, corneal leucoma was observed in froup A, ring ulcer formed in group B and serious descemetocele showed in Group C. During the process, the infections in group C developed earlier, more serious and more representative than that in groups A and B in this study.

Fig. 4

HE staining of corneal sections of rats. The picture of "0 d" is the corneal section of normal mice in which the epithelium and stroma are well-defined and there are no inflammatory cells infiltrated. In the corneal sections with Acanthamoeba treatment, the inflammatory cells infiltrate, necrotic tissue appears, and normal structure of the cornea is destroyed. After 13 days, neovasculation appears and the regular stromal fibers are gradually replaced by unorganized collagen fibers (Original magnificence:×200).