الفهرس 
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Abstract
Amoebiasis is a protozoal disease caused by acellular, anaerobic parasitic protistan called Entamoeba histolytica. Amoebiasis is the third leading cause of death after malaria related to parasitic diseases worldwide. Entamoeba histolytica is spread via the feco-oral route. There are two forms of this parasite; the infective cyst stage, which can be ingested from a contaminated source, either water or food, then the cysts decapsulate in the intestine of the host, as they are acid resistant. The invasive-colon trophozoite stage which migrates to the colon, where they multiply and may pass through the epithelium into the submucosa or enter the blood vessels to get access to the extraintestinal tissues. Some are re-encysted to be excreted in faeces.
Amoebiasis can cause harm not only to the intestines, where cysts decapsulate, release amoebulae, and invade the villi wall, but it can also have a disastrous effect on the liver, the lungs, and the brain, which impair the adult productivity, as well as the childhood development, increasing the susceptibility to other infections.
Only limited numbers of drugs are available for the treatment of amoebiasis. Among them is albendazole, which has been used for many years. However, its side effects and indiscriminate use, which may cause drug resistance in future, limit its use. So, searching for a natural extract as either a replacement for, or a complement to the drug is a must nowadays.
Carica papaya is a succulent fruit of a large plant of the family Caricaceae. It contains many biologically active compounds, including phenolic compound, in its different parts which act as a miracle in disease cure and prevention through modulation of various activities, including antioxidant, anti-inflammatory, anti-tumor, and hepatoprotective effects (Rahmani et al., 2016). Interestingly, the aqueous extracts of the C. papaya caused a significant reduction in the cysts burden in CD-1 mice infected with E. histolytica (Mohammed et al., 2014).
The present study was conducted to investigate the role of C. papaya fruit extract as therapeutic drug against murine entamoebiasis histolytica. To evaluate that papaya methanolic (MeOH) extract was prepared and subsequently used for investigation.
Each of two main groups of male CD-1 mice (50/each), the immuno-suppressed and immuno-competent groups, was subdivided equally into 5 sub-groups: normal, infected and infected-treated with 500 mg/kg of crude or pure C. papaya extracts or 200 mg/kg of albendazole. Immune suppression was induced by using dexamethasone orally at a dose of 0.25 mg/g/day for 14 successive days prior to oral infection with 1000 E. histolytica cysts/mouse. Three doses/week of extracts were administered orally to infected mice for 3 weeks. Six weeks post infection; all animals were sacrificed for parasitological, immunological, and histological parameters.
Parasitological findings, the immuno-competent groups showed that treatment with either crude or pure defatted MeOH extracts reduced parasite appearance in intestinal fluid by 76.29% and 78.20% and in stool by 60% and 70%, respectively. While in albendazole treated group, the reduction of parasites was 88.72% and 83.30% in intestinal fluid and stool, respectively. Immunologically, mice treated with C. papaya fruit MeOH extract or albendazole displayed a significant (P< 0.001) reduction in the serum levels of IgG, IgM, and IgA antibodies compared with infected control. Detectable levels of circulating IFN- were also recorded in infected as well as treated groups, which decreased significantly (P< 0.05) in treated infected mice compared with untreated infected ones. Regarding histopathological findings, Albendazole and pure extracts caused obvious improvement for the majority of the liver and small intestine tissues. The crude extract had a repairing effect on the tissues as well, but not in a complete form, as we can still see some of the necrosis and infiltration of lymphocytes.
Importantly, the results of the immuno-suppressed groups were similar to those of the immuno-competent ones, but with non-significant lower levels. The findings together indicate that C. papaya fruit MeOH extract may be effective in treating E. histolytica.