Epidemiological studies on zoonotic leishmaniasis and new trials for studying the effect of melatonin on the parasite

Abstract

Leishmaniasis remains an important public health problem caused by protozoan of genus Leishmania and transmitted by the bite of a female phlebotomine sand fly. Humans, rodents, and some animal species are considered reservoir for the disease. Among other animal species, the dogs are the most important reservoirs in a domestic environment, maintaining the endemic focus of the parasite. The disease has been also linked to tropical and subtropical regions besides being an endemic disease in the Mediterranean basin and South America. Depending on the infecting parasite species and host immune response, three forms of the disease are known: cutaneous, mucocutaneous, and disseminated visceral leishmaniasis of fatal prognosis. The recent years have witnessed extraordinary potential progress and ever growing in organ transplantation worldwide as a consequence of sustained economic growth and the higher investments in tertiary healthcare policies in many developing countries. Spain is widely known as one of the countries with the highest transplant rates. As result of lack of routine serology for blood or organ donors in areas of high endemicity, transplanted recipients are susceptible to a broad spectrum infectious agents resulting in different symptoms. Leishmania is considered one of opportunistic infections but it is not common disease among transplanted patients, however, the growing pool of transplant survivors and high migration dynamics steadily increases the numbers of infected cases among transplant recipients especially among renal transplanted recipients mainly in southern Europe, particularly with visceral leishmanisis (VL). Despite several leishmanial researches, many questions are still unanswered. Early case detection followed by adequate treatment represents the key to the control of the disease that may improve the prognosis and can reduce transmission. Diagnosis of Leishmania infection is still somewhat controversial due to absence of gold standard technique that appears mandatory to establish effective strategic programmes. Current tools of diagnosis are several and they rely mainly on parasite detection by microscopic examination or by molecular biology-based assays for detecting parasite DNA (PCR) but none of these methods have become popular in field diagnosis. The conventional parasitological techniques are also risky, time consuming, invasive for the patient and require skilled personnel. The molecular methods also require the availability of software, probes and primers, which cannot easily applied especially in field settings and still not affordable for many clinical and scientific laboratories in developing countries. Interestingly, serological diagnosis using several tests is an alternative tool for the parasitological diagnosis; can be used for a large-scale and decentralized diagnosis, however, all the serological techniques share many drawbacks like that related to sensitivity or specificity have been reported. On the other hand, the presence of different Leishmania species and various manifestations also complicates the therapeutic approach, especially in immunocompromised patients. A limited number of effective antileishmanial agents are available for chemotherapy, and many of them are expensive with severe side effects or have a markedly reduced effectiveness due to the development of drug resistance. Based upon several published works, plants have different biologically active compounds in their organs, which can be pharmacologically studied. Melatonin is an indoleamine synthesized and released by several organs. Several studies have included the relationship between melatonin and many parasitic or viral diseases. Given above information, there is a genuine need to develop a novel effective and less toxic antileishmanial drug for amelioration of patient’s life quality besides the necessity for surveying strategy using a rapid and reliable diagnostic test in one of animal reservoirs in certain endemic area (cats). The scheduling of the thesis has been divided into several phases: the first part includes reviews of the literature about current status of epidemiology, development in diagnosis and treatment of the disease for better understanding the gaps in disease management. The second part of the thesis, the experimental part, includes two phases; the first phase of the present work included a serological study about Leishmania infection among transplanted organ recipients from southern Spain followed by assessment of the occurrence of Leishmania infantum in domestic cats from an endemic region in North-western Italy, by the association of both serological and molecular tests. In the second phase of our work, we have studied the effect of melatonin against the parasite in vitro. Our results provide an evidence that a relatively high prevalence of L.infantum was recorded among kidney transplanted recipients, where 30 (4.08%) samples were positive for L. infantum out of 625 examined serum samples. Regarding the cross sectional survey in cats, we have found that 33 samples (13.12%) were positive for L. infantum out of 250 examined serum samples from cats, whereas of the 282 blood samples, 80 (28.37%) were positive. In accordance with therapeutic trials, melatonin not only demonstrated a significant antileishmanial activity in vitro but was also accompanied by an alteration of the several mitochondrial parameters, including calcium homeostasis and by changes in some mitochondrial parameters critical to parasite survival. These multiple results suggest that 1) the routine serological testing for VL should be initially considered before undergoing transplantation for both donor and recipient transplant patients living or traveling in endemic areas to prevent such serious post-transplantation infection, 2) High prevalence of L.infantum among cats in the studied area which show the importance of cats not only as reservoir for the disease, but also the need for further future research for accurate diagnosis of this zoonosis, 3) Western blot and PCR would be a novel potential tools in diagnosis of Leishmania infection in cat, and 4) melatonin may be a potent antileishmanial agent, and therefore further research is warranted to elucidate the effects of melatonin in vivo and in association with other antileishmanial drugs combined with examination the role of melatonin receptors in these effects and their underlying mechanisms. These observations together could be of special attention for the people to identify the risk factors of transmission of such protozoan and would be helpful in earlier detection, treatment and as a consequence in eradication of this neglected disease.