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Leishmaniasis is a tropical parasitic disease that has become a major health challenge in many countries of the world. Not only has not been found any effective vaccine or treatment for the disease eradication, but also the advent of drug resistance is also increasing. Therefore, it is vital to take a precise attention to the physiochemical cycles of the Leishmania parasite and to identify its biochemical pathways. One of the most important biochemical pathways of host and parasite is the arginase and nitric oxide cycles. By using L-arginine, arginase plays an important role in the metabolic pathways, particularly in ornithine production, polyamines biosynthesis and cellular activities, including proliferation and cell survival. Furthermore, L-arginine, can act as a substrate for inducible nitric oxide synthase (iNOS), which leads to the synthesis of nitric oxide (NO), thereby activating the cellular immune system and clearing intracellular parasites. High Arginase activity reduces the parasite load inside the host cell, and since lymphocytes need L-arginine for their activity, its deficiency impairs the response of host immune cells. Also, parasites arginase alone can determine the fate of Leishmania parasite within the host cell. The aim of this study was to provide a comprehensive overview of various studies on the arginase activity of both parasite and host and its direct impacts on the immune system and pathogenicity of the Leishmania parasite.
 

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Background: Pneumocystis jirovecii (P. jirovecii) causes Pneumocystis pneumonia (PCP) in people, especially the immunocompromised ones. It is also one of the serious causes of numerous lung problems in affected patients. Since documented data about P. jirovecii is not available in patients with pulmonary infections in Tehran, this study aimed to investigate the molecular epidemiology and parasitology of Pneumocystis to determine the frequency of the organism infection.
Methods: Bronchoalveolar lavage (BAL) samples were collected for 367 patients hospitalized in the lung department of Shariati Hospital in Tehran from July 2022 to July 2023. The samples were analyzed using Giemsa staining and molecular methods. After DNA extraction from samples, Nested polymerase chain reaction (Nested PCR) was employed for the amplification of the 18SrRNA gene and identification of P. jirovecii. The PCR products of Nested PCR were sequenced for final confirmation. 
Results: Out of 367 samples, only one sample (0.27%) and 28 samples (6.7%) were found to be positive through parasitology and NestedPCR analysis, respectively. P. jirovecii was detected in seven (25%) and 21 (75%) immunocompromised and immunocompetent patients, respectively. Fever, shortness of breath and dry cough were the most common clinical symptoms among patients with Pneumocystosis. Patients with pulmonary disorders are prone to colonization by pneumocystis, which increases the risk of pneumocystosis and makes them a reservoir for transmission to susceptible people.
Conclusion: It can be concluded that patients with distinct lung disease are prone to colonization by Pneumocystis and, importantly, are at risk of infection. Also, according to the current study, Nested PCR was a suitable method for detecting P. jirovecii organisms because it had a very high sensitivity and specificity.