Case report

A 36-year old female patient was admitted to a government hospital complaining of recurrent fever with chills for last two months along with generalised weakness and loss of appetite. She neither had past medical history of serious illness nor had any overseas travel history. The physical examination was notable for an enlarged spleen and weight loss. The results of haematological examination showed severe anemia with  changes in red blood cell morphology and severe leukopenia. For further investigation, medical practitioners suggested to perform whole abdomen ultrasonography (USG). They found splenomegaly extended to the pelvic region along with larger liver. The medical team suspected some parasitic infection, they decided to perform bone marrow aspiration and biopsy. The results of bone marrow pathology revealed the typical appearance of leishmania with distinct nucleus and mitochondria. Molecular diagnostics analysis using Polymerase Chain Reaction (PCR) confirmed that Leishmania donovani infections ultimately resulted in visceral leishmaniasis (VL) in the patient. Thereafter  the patient was treated with amphotericin B for about one month. The symptoms were gradually subsided and her general health conditions were improved (1,2). The important point to be noted that the current treatment of VL cannot make  the patient  complete sterile cure. Parasites reside intracellularly and may relapse in immunosuppressive condition. Scientific communities  are interested to invest more attention  in the development of novel therapeutic agents  as well as the evaluation of combination therapies with existing drugs for complete cure of VL. In the perspective of global public health, further research on leishmania is urgently required to combat the diseases.

Leishmania and leishmaniasis

Leishmania species are unicellular protozoan parasites belongs to genus Kinetoplastida. It consists complex life cycle that alternate between insect and mammalian hosts. Phlebotomine sandflies is the vector and it is transmitted through inoculation of promastigote (insect stage form) to human skin during insect bite (Figure 1). In human host, parasites encountered several developmental changes and converted to amastigote forms (mammalian host form).The intracellular parasites ultimately infect the immune cells of reticulo-endothelial system and affect spleen, bone marrow, liver etc. There are three main forms of leishmaniases 1) visceral (also known as kala-azar), cutaneous (the most common) and mucocutaneous. Kala-azar (KA) or visceral leishmaniasis, is the most prevalent form of 

Figure 1: Life cycle of L. donovani.

L. donovani exhibits complex life cycle that alternate between two host system. In insect midgut  it is found in flagellated form (promastigote). It is transmitted to human by sandfly bites and developed to amastigote intracellularly in human host (4).

leishmaniasis in India. The disease is caused by the parasite L. donovani. Leishmaniasis is considered as a Neglected Tropical Diseases (NTDs) and occurs mainly in the countries of Africa, Latin America as well as Indian subcontinent (Figure 2). NTDs are a group of tropical infections commonly found in the low-income population of developing countries. World Health Organization (WHO) endorsed twenty diseases as NTDs, caused by a variety of pathogens such as viruses, bacteria, protozoa etc. It is associated with malnutrition, population displacement, poor housing, and environmental sanitation, lack of personal protective measures all cumulatively responsible for the deterioration of community public health. The lack of research funding, clinical attention and awareness demand more efforts on the prevention and control of NTDs for the betterment of global public health (3).

Figure 2. The current status of endemicity of visceral leishmaniasis (VL) worldwide.

The number of new VL cases are presented by different colour code in the world map. Data source: WHO map production, control of NTDs.

Treatment and prevention strategies

Treatment of Leishmaniasis solely depends on species detection and health condition of the patient (e.g. pregnancy, immunosuppression). The major limitation of the current treatment is its incapability to make the patient complete sterile cured. The parasite remains in the human body and relapses in  immunosuppressive conditions. Most of the drugs used for the therapy of Leishmaniasis are antimonial preparations such as sodium stibogluconate (pentostam) and meglumine antimonate (glucantime) and are known as first-line drugs. Antimonials exert adverse side effects such as cardiac arrhythmia and acute pancreatitis and are sometimes life-threatening. The second-line drugs like amphotericin B, miltefosine, and paromomycin although clinically used are all severely toxic. The major challenge for the prevention of the diseases is to avoid being bitten by an infected female sandfly. Anti-malarial insecticide (dichloro-diphenyl-trichloroethane (DDT)) spraying campaigns were very effective for vector control (Figure 3) and consequently disappearances of VL in the Indian subcontinent (4). 

Figure 3: Vector control by spraying insecticides in high kala-azar area.

Sandflies are susceptible to the same insecticides as Anopheles mosquitoes (the malaria vector).  DDT spaying campaign is very effective for vector control for Leishmaniasis in India. Adopted from WHO India website.

Future prospect 

The appearance of drug-resistant  strains is the major challenging job for drug design against the parasites. Leishmania has already developed resistance against first line drugs (antimonial). Researchers are interested to decipher the mechanism of drug resistance in leishmania and try to identify newer targets. The existing drugs used for the treatments are toxic, infusion and expensive. Trypanosoma brucei (a similar type of parasite), is extensively used as a model organism for genomic, proteomics studies. These parasites (Trypanosomes) exert few biological features which are distinct in the parasite but not found in the host system. The basic science discoveries of trypanosomes can be translated to the therapeutic intervention or vaccine development program of Leishmaniasis. International Institute of Innovation and Technology, (I3TK) in Kolkata, India in collaboration with The Johns Hopkins Bloomberg School of Public Health (JHSPH), USA has taken an initiative to target NTDs like Leishmaniasis, Dengue fever along with Malaria for its research and development program to support global public health. The major focus of the studies will be to identify novel target pathway in leishmania for drug and vaccine development. DNA damage and repair machineries of the parasites are promising targets for new drug intervention. Induction of DNA damage by treatment of genotoxic agents is one of the well-established strategies to kill parasites (5,6). The research team of I3TK will focus on DNA damage and repair pathways of leishmania that will be targeted by small molecule inhibitors. For this purpose, the development of high throughput drug screening assay will be established. The research team will employ recombinant DNA technology and other molecular biology techniques to decipher the mechanism of drug targeting. Moreover, a global transcriptomic analysis of the leishmania will be performed by Next Generation Sequencing (NGS) technology (7). These studies will provide  a large set of data to understand the metabolomics of host pathogen interaction studies for further translational and basic research. Moreover the research strategies utilised for these studies will be extended to other studies involving parasites like Plasmodium (causative agent for malaria). 

References

1. Taghavi, M.R., Mollazadeh, S., Seddigh-Shamsi, M., Azimian, A., Mianji, M., Mohajerzadeh Heydari, M.S., Zandi, Z. and Shokri, A. (2020) Visceral leishmaniasis in an adult case in Northeast of Iran: A case report and literature review. Clinical Case Reports, 8, 3207-3211.

2. Ghimire, P.G., Ghimire, P., Adhikari, J. and Chapagain, A. (2019) A case report of visceral leishmaniasis and malaria co-infection with pancytopenia and splenomegaly – a diagnostic challenge. BMC Infectious Diseases, 19, 849.

3. Casulli, A. (2021) New global targets for NTDs in the WHO roadmap 2021-2030. PLoS neglected tropical diseases, 15, e0009373-e0009373.

4. Chappuis, F., Sundar, S., Hailu, A., Ghalib, H., Rijal, S., Peeling, R.W., Alvar, J. and Boelaert, M. (2007) Visceral leishmaniasis: what are the needs for diagnosis, treatment and control? Nature Reviews Microbiology, 5, 873-882.

5. Mishra, A., Vinayagam, J., Saha, S., Chowdhury, S., Chowdhury, S.R., Jaisankar, P. and Majumder, H.K. (2014) Isobenzofuranone derivatives exhibit antileishmanial effect by inhibiting type II DNA topoisomerase and inducing host response. Pharmacol Res Perspect, 2, e00070.

6. Klebanov-Akopyan, O., Mishra, A., Glousker, G., Tzfati, Y. and Shlomai, J. (2018) Trypanosoma brucei UMSBP2 is a single-stranded telomeric DNA binding protein essential for chromosome end protection. Nucleic Acids Research, 46, 7757-7771.

7. Mishra, A., Kaur, J.N., McSkimming, D.I., Hegedűsová, E., Dubey, A.P., Ciganda, M., Paris, Z. and Read, L.K. (2021) Selective nuclear export of mRNAs is promoted by DRBD18 in Trypanosoma brucei. Mol Microbiol, 116, 827-840.