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Leishmania parasites as the causative agent of leishmaniasis belong to Trypanosomatidae family. Parasite, vector, vertebrate host and environment are major factors in pathogenesis of Leishmania. 
Parasite dependent factors are virulence factors which exist in Leishmania species such as LPG, GP63. In recent years, the importance of these factors in the field of vaccine and drug has been considered by researchers. Sand fly biting behavior and salivary gland proteins are vector dependent factors which are effective in the Leishmania pathogenesis. Age, gender, nutrition, immune system, infectious diseases, genetic, occupation, socio-economic characteristics, and habitat are vertebrate host mediated factors. Temperature, rainfall, wind and its speed, soil, and continuous changes in climate are also environmental factors. Therefore the aim of this study was to evaluate the pathogenesis of Leishmania parasites.
 

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Background: Opportunistic pathogens such as Cryptosporidium, Isospora belli, Blastocystis, etc. cause various gastrointestinal and non-digestive diseases in people with HIV. These symptoms are especially severe in people with HIV who have a CD4 count of less than 200. This study aimed to determine the prevalence of parasitic infections in people living with HIV in Tabriz.
Methods: This cross-sectional and descriptive study was performed on137 people with HIV referred to Behavioral Disease Counseling Centers in Tabriz, 2019-2021. Then, after receiving written consent, fecal samples were collected and evaluated for the detection of parasitic infections using direct methods, Ziehl-Neelsen and Trichrome Weber stain.
Results: A total of 137 stool samples were collected, including 93 males and 44 females. Most of them were in the age range of 20-60 years. The overall frequency of parasitic infections was 57.7% and the highest prevalence was related to Blastocystis 24.1% and Cryptosporidium 14.6%.
Conclusion: Due to the relatively high prevalence of parasitic infections, especially Blastocystis and Cryptosporidium in people with HIV in Tabriz, which can endanger the health of these patients, essential interventions, including personal hygiene training to control and prevent infection with these pathogens, seem to be necessary.