Previous exposure to a low infectious dose of Leishmania major exacerbates infection with Leishmania infantum in the susceptible BALB/c mouse

Leishmaniasis in Cameroon and neighboring countries: An overview of current status and control challenges

Leishmaniasis causes the ninth largest disease burden among infectious diseases but remains a very neglected tropical disease. Although the disease is endemic in Cameroon and some neighboring countries, data on its epidemiology are very scanty. The present review summarizes the available information on leishmaniasis in the central region of Africa. According to available records, Cameroon, Chad and Nigeria have been identified as endemic foci of both cutaneous (CL) and visceral leishmaniasis (VL). In addition, the phlebotomine vectors of leishmaniasis have been reported in these three countries and also in Congo and the Central African Republic. Although Gabon, Central African Republic, Equatorial Guinea and Congo are all situated next to the above leishmaniasis-endemic countries and are characterized by similar landscapes and vegetation, they lack published reports of autochthonous cases of leishmaniasis. Considering that many cases of the disease might remain unreported, it might not be an overstatement to recommend that research should be carried out in Gabon, Equatorial Guinea, Central African Republic and Congo to identify cases of leishmaniasis (CL and/or VL), the parasite and vector species, and the mammalian reservoir host. This review updates data on leishmaniasis and its insect vector in the geographical region of Central Africa. Such updates are basic requirement for the development of successful control programmes in individual countries and the whole region. In order to address the shortcomings identified in the present review, the authors recommend training of more scientists in leishmaniasis epidemiology in the region that should be accompanied by necessary funding. This training must be multidisciplinary and include development of laboratory and field skills for studies of the parasite, the vector, the reservoir, the vegetation and the soil in potential endemic foci. In addition, prospective studies involving geographers and other experts should develop a disease risk map of the Central Africa region.

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.

Investigations on the effects of anti-Leishmania major serum on the progression of Leishmania infantum infection in vivo and in vitro - implications of heterologous exposure to Leishmania spp

Leishmaniasis is a vector-borne parasitic disease caused by protozoa of the genus Leishmania. Twenty different species are known to cause disease in humans with varying degrees of pathology. These diseases are transmitted throughout the geographic range of phlebotomine sandflies, found between the latitudes 50°N and 40°S. This study explores antibody dependent enhancement (ADE) as the cause of disease exacerbation in heterologous exposure of L. major primed mice to L. infantum challenge. BALB/c mice received serum from L. major infected or naive mice. All mice were challenged with L. infantum and tissue parasite burdens were recorded. Animals that received anti-L. major serum exhibited significantly higher parasite burdens. Surprisingly, these parasite burdens were higher than those of mice infected with L. major and challenged with L. infantum. In vitro phagocytosis assays were carried out to measure parasite uptake in the presence of naive vs. anti-L. major serum. J774A.1 murine monocytes were cultured with either L. major or L. infantum in the presence of anti-L. major serum, naive serum, or no serum. Significantly higher rates of L. major uptake by J774A.1 cells occurred in the presence of anti-L. major serum, but no measurable increase of L. infantum phagocytosis was seen. Our results suggest that increased disease severity observed in vivo in mice previously exposed to L. major and challenged with L infantum is not a result of extrinsic ADE. We speculate that intrinsic ADE, due to biased memory T cell responses caused by Fcγ signaling, could account for disease exacerbation seen in the animal model.

Long-term hexavalent chromium exposure facilitates colorectal cancer in mice associated with changes in gut microbiota composition

Colorectal cancer (CRC) is among the leading causes of cancer-related mortality worldwide. Hexavalent chromium [Cr(VI)] is often present in groundwater. Chronic Cr(VI) exposure is suggested to be one of the main factors inducing cancer. However, the correlation between Cr(VI) and CRC remains unclear. In this study, we investigated the role of Cr(VI) in CRC by establishing a mouse CRC model induced by 1, 2-dimethylhydrazine (DMH). The results showed that Cr(VI) increased weight loss in DMH-induced mice and promoted the formation of tumors. Cr(VI) also increased DMH-induced proliferating cell nuclear antigen (PCNA) levels. Investigation of the underlying mechanisms found that Cr(VI) significantly decreased DMH-induced SOD, GSH and CAT levels, while, the MDA level increased. Metagenomic analyses found that the abundance of Firmicutes and Bacteroidetes in the DMH + Cr group was down-regulated. Interestingly, the combination of Cr(VI) and DMH significantly increased the abundance of Verrucomicrobia. At the family and genus levels, families Akkermansiaceae and Saccharimonadaceae and genus Akkermansia were more abundant in the DMH + Cr group, whereas the abundance of short-chain fatty acid (SCFA)-producing bacteria (family Muribaculaceae, family Lachnosipiraceae, genus Lachnospiraceae_NK4A136_group, and genus Roseburia) decreased. These results indicate that Cr(VI) might aggravate CRC by altering the composition of the gut microflora.

Vaccination with a Leishmania infantum HSP70-II null mutant confers long-term protective immunity against Leishmania major infection in two mice models

Background

The immunization with genetically attenuated Leishmania cell lines has been associated to the induction of memory and effector T cell responses against Leishmania able to control subsequent challenges. A Leishmania infantum null mutant for the HSP70-II genes has been described, possessing a non-virulent phenotype.

Methodology/Principal findings

The L. infantum attenuated parasites (LiΔHSP70-II) were inoculated in BALB/c (intravenously and subcutaneously) and C57BL/6 (subcutaneously) mice. An asymptomatic infection was generated and parasites diminished progressively to become undetectable in most of the analyzed organs. However, inoculation resulted in the long-term induction of parasite specific IFN-γ responses able to control the disease caused by a challenge of L. major infective promastigotes. BALB/c susceptible mice showed very low lesion development and a drastic decrease in parasite burdens in the lymph nodes draining the site of infection and internal organs. C57BL/6 mice did not show clinical manifestation of disease, correlated to the rapid migration of Leishmania specific IFN-γ producing T cells to the site of infection.

Conclusion/Significance

Inoculation of the LiΔHSP70-II attenuated line activates mammalian immune system for inducing moderate pro-inflammatory responses. These responses are able to confer long-term protection in mice against the infection of L. major virulent parasites.

Despite numerous efforts made, a vaccine against leishmaniasis for humans is not available. Attempts based on parasite fractions or selected antigens failed to confer long lasting protection. On the other side, leishmanization, which consists in the inoculation of live virulent parasites in hidden parts of the body, is effective against cutaneous leishmaniasis in humans but objectionable in terms of biosafety. Some efforts have been made to design live vaccines to make leishmanization safer. A promising strategy is the development of genetically attenuated parasites, able to confer immunity without undesirable side effects. Here, we have employed an attenuated L. infantum line (LiΔHSP70-II) as a vaccine against heterologous challenge with L. major in two experimental models. Infection with LiΔHSP70-II parasites does not cause pathology and induces long-term protection based on the induction of IFN-γ producing T cells that are recruited rapidly and specifically to the site of challenge with the virulent parasites. These results support the idea of using attenuated parasites for vaccination.

Cutaneous Infection with Leishmania major Mediates Heterologous Protection against Visceral Infection with Leishmania infantum

Visceral leishmaniasis (VL) is a fatal disease of the internal organs caused by the eukaryotic parasite Leishmania. Control of VL would best be achieved through vaccination. However, this has proven to be difficult partly because the correlates of protective immunity are not fully understood. In contrast, protective immunity against nonfatal cutaneous leishmaniasis (CL) is well defined and mediated by rapidly recruited, IFN-γ-producing Ly6C(+)CD4(+) T cells at the dermal challenge site. Protection against CL is best achieved by prior infection or live vaccination with Leishmania major, termed leishmanization. A long-standing question is whether prior CL or leishmanization can protect against VL. Employing an intradermal challenge model in mice, we report that cutaneous infection with Leishmania major provides heterologous protection against visceral infection with Leishmania infantum. Protection was associated with a robust CD4(+) T cell response at the dermal challenge site and in the viscera. In vivo labeling of circulating cells revealed that increased frequencies of IFN-γ(+)CD4(+) T cells at sites of infection are due to recruitment or retention of cells in the tissue, rather than increased numbers of cells trapped in the vasculature. Shortly after challenge, IFN-γ-producing cells were highly enriched for Ly6C(+)T-bet(+) cells in the viscera. Surprisingly, this heterologous immunity was superior to homologous immunity mediated by prior infection with L. infantum. Our observations demonstrate a common mechanism of protection against different clinical forms of leishmaniasis. The efficacy of leishmanization against VL may warrant the introduction of the practice in VL endemic areas or during outbreaks of disease.

Leishmanization revisited: immunization with a naturally attenuated cutaneous Leishmania donovani isolate from Sri Lanka protects against visceral leishmaniasis

Leishmaniasis is a neglected tropical disease caused by Leishmania protozoa and associated with three main clinical presentations: cutaneous, mucocutaneous and visceral leishmaniasis. Visceral leishmaniasis is the second most lethal parasitic disease after malaria and there is so far no human vaccine. Leishmania donovani is a causative agent of visceral leishmaniasis in South East Asia and Eastern Africa. However, in Sri Lanka, L. donovani causes mainly cutaneous leishmaniasis, while visceral leishmaniasis is rare. We investigate here the possibility that the cutaneous form of L. donovani can provide immunological protection against the visceral form of the disease, as a potential explanation for why visceral leishmaniasis is rare in Sri Lanka. Subcutaneous immunization with a cutaneous clinical isolate from Sri Lanka was significantly protective against visceral leishmaniasis in BALB/c mice. Protection was associated with a mixed Th1/Th2 response. These results provide a possible rationale for the scarcity of visceral leishmaniasis in Sri Lanka and could guide leishmaniasis vaccine development efforts.