Granuloma Formation During Parasitic Infections Once parasites initiate an infection, they can effectively resist the lethal effects of macrophages and produce a chronic infection that can lead to inflammation. Parasites can induce granulomatous inflammation that serves to isolate pathogens that resist destruction ( 58 ). These granulomas are regulated by T cells that recognize antigens released by the parasites. In tissues, macrophages accumulate and secrete chemicals that induce fibrosis and stimulate the formation of granulomatous tissue and cause fibrosis. During infection with Schistosoma spp, granuloma formation develops around the eggs (59) (see chapter 4). Numerous ova are transported to the liver where they are isolated behind a capsule containing different types of inflammatory cells (59). In experiments conducted on mice, granuloma formation consists predominantly of eosinophils and is the result of a T cell-dependent reaction (59). In visceral leishmaniasis, parasites frequently spread to the liver, spleen, lymph nodes and bone marrow. This spread of the parasite produces an enlargement of the liver and spleen in a condition known as hepatosplenomegaly. Fever, abdominal pain and weight loss are some of the symptoms associated with this condition. The disease is fatal if left untreated, due to numerous complications such as secondary infections, anemia, and malnutrition (60). In visceral leishmaniasis, fever, paleness, weakness, night sweats, anorexia, and weight loss are common and progress to a medical condition known as cachexia (wasting syndrome), a general wasting condition associated with the overproduction of TNF- (also known as as cachexin). ). Children with visceral leishmaniasis may develop diarrhea and growth retardation... half of the paper... unit plays an important role in the development of intestinal pathology during experimental and human giardiasis. Again, the uncontrolled response of this T cell immunity could be harmful to the host by inducing collateral tissue damage. CONCLUSION Parasitic diseases constitute a serious health problem worldwide, especially affecting poor countries. The World Health Organization has identified several parasitic diseases as among the most important worldwide. These diseases include malaria, Chagas disease, leishmaniasis, filariasis, and schistosomiasis. Tissue damage and death induced by parasitic infections occur mostly after chronic infections and, depending on the type of infection, different organs are affected. A better understanding of the molecular mechanisms of these diseases will be useful in identifying targets for developing therapeutic prototypes and vaccines.