Beyond schistosomiasis: unraveling co-infections and altered immunity.

Schistosomiasis is a neglected tropical disease caused by the helminth Schistosoma spp. and has the second highest global impact of all parasites. Schistosoma are transmitted through contact with contaminated fresh water predominantly in Africa, Asia, the Middle East, and South America. Due to the widespread prevalence of Schistosoma, co-infection with other infectious agents is common but often poorly described. Herein, we review recent literature describing the impact of Schistosoma co-infection between species and Schistosoma co-infection with blood-borne protozoa, soil-transmitted helminths, various intestinal protozoa, Mycobacterium, Salmonella, various urinary tract infection-causing agents, and viral pathogens. In each case, disease severity and, of particular interest, the immune landscape, are altered as a consequence of co-infection. Understanding the impact of schistosomiasis co-infections will be important when considering treatment strategies and vaccine development moving forward.

Production of leishmanin skin test antigen from Leishmania donovani for future reintroduction in the field.

The leishmanin skin test was used for almost a century to detect exposure and immunity to Leishmania, the causative agent of leishmaniasis, a major neglected tropical disease. Due to a lack of antigen used for the intradermal injection, the leishmanin skin test is no longer available. As leishmaniasis control programs are advancing and new vaccines are entering clinical trials, it is essential to re-introduce the leishmanin skin test. Here we establish a Leishmania donovani strain and describe the production, under Good Laboratory Practice conditions, of leishmanin soluble antigen used to induce the leishmanin skin test in animal models of infection and vaccination. Using a mouse model of cutaneous leishmaniasis and a hamster model of visceral leishmaniasis, soluble antigen induces a leishmanin skin test response following infection and vaccination with live attenuated Leishmania major (LmCen-/-). Both the CD4+ and CD8+ T-cells are necessary for the leishmanin skin test response. This study demonstrates the feasibility of large-scale production of leishmanin antigen addressing a major bottleneck for performing the leishmanin skin test in future surveillance and vaccine clinical trials.

Investigating the Leishmania donovani sacp Gene and Its Role in Macrophage Infection and Survival in Mice.

The protozoan parasite Leishmania donovani is a causative agent of the neglected tropical disease known as visceral leishmaniasis, which can be lethal when untreated. Studying Leishmania viru-lence factors is crucial in determining how the parasite causes disease and identifying new targets for treatment. One potential virulence factor is L. donovani's abundantly secreted protein: secreted acid phosphatase (SAcP). Whole-genome analysis revealed that the sacp gene was present in three copies in wild type L. donovani. Using CRISPR-Cas9 gene editing; we generated a sacp gene knockout termed LdΔSAcP, which demonstrated a loss of both the SAcP protein and an associated reduction in secreted acid phosphatase activity. Genome sequencing confirmed the precise dele-tion of the sacp gene in LdΔSAcP and identified several changes in the genome. LdΔSAcP demonstrated no significant changes in promastigote proliferation or its ability to infect and survive in macrophages compared to the wildtype strain. LdΔSAcP also demonstrated no change in murine liver infection; however, survival was impaired in the spleen. Taken together these results show that SAcP is not necessary for the survival of promastigotes in culture but may support long-term survival in the spleen. These observations also show that the use of CRISPR gene editing and WGS together are effective to investigate the function and phenotype of complex potential drug targets such as multicopy genes.

An intraspecies Leishmania donovani hybrid from the Indian subcontinent is associated with an atypical phenotype of cutaneous disease.

Leishmaniasis is a neglected tropical disease endemic in over 90 countries. The disease has two main pathologies; cutaneous leishmaniasis (CL) that generally self-heals, and visceral leishmaniasis (VL) that is fatal if untreated. The majority of VL cases, concentrated on the Indian subcontinent (ISC) and East Africa, are caused by Leishmania donovani. However, recent foci of CL on the ISC have been attributed as an atypical phenotype of L. donovani including a recent outbreak in Himachal Pradesh, India. Whole genome sequencing and phylogenetic analysis was undertaken to investigate the origins and genetic factors leading to this pathology atypical of L. donovani. Here we demonstrate the isolate from Himachal Pradesh is derived from a genetic hybridization between two independent L. donovani parents from the 'Yeti' ISC1 divergent clade of parasites, identified in the Nepalese highlands. This reveals that intraspecies L. donovani hybrids can give rise to a novel strain associated with CL.

A review of the leishmanin skin test: A neglected test for a neglected disease.

The leishmanin skin test (LST) has been used for decades to detect exposure and immunity to the parasite Leishmania, the causative agent of the neglected tropical disease leishmaniasis. In the LST, Leishmania antigen (leishmanin) is intradermally injected into the forearm. In an individual who has been previously infected, a delayed-type hypersensitivity (DTH) reaction results in a measurable induration at the site of the injection, indicating that previous exposure to Leishmania has resulted in the development of cell-mediated immunity. LST positivity is associated with long-lasting protective immunity against reinfection, most notably as reported for visceral leishmaniasis (VL). Despite efforts over the past few decades, leishmanin antigen is no longer produced under good manufacturing practice (GMP) conditions anywhere in the world. Consequently, the use of the LST in epidemiological studies has declined in favor of serological and molecular tests. In this review, we provide a historical overview of the LST and justification for the reintroduction of leishmanin. A GMP-grade leishmanin can be used to detect immunity in vivo by the LST and can be investigated for use in an interferon-γ release assay (IGRA), which may serve as an in vitro version of the LST. The LST will be a valuable tool for surveillance and epidemiological studies in support of the VL elimination programs and as a surrogate marker of immunity in vaccine clinical trials. METHODS: A review of the literature was conducted using PubMed as the primary database, with MeSH terms "leishmanin skin test" OR "Montenegro test" OR "Montenegro skin test." Articles written in English that describe the history or standardization of leishmanin, the use of leishmanin in an IGRA, or the use of the LST in epidemiological studies or vaccine trials were prioritized in our appraisal of the literature.