Liposomal chemotherapy in visceral leishmaniasis: an ultrastructural study of an intracellular pathway

The intracellular fate of liposomes administered intracardially was examined in the liver and spleen of hamsters experimentally infected with Leishmania donovani. Separate groups of animals were treated with liposomes containing either an antileishmanial agent, a colloidal gold marker, or saline. Ultrastructural examinations of lysosomal interactions with the parasitophorous vacuole and with phagocytized liposomes were made. Lysosomes readily fused with the parasitophorous vacuoles but appeared to have little effect on the parasite, possibly due to the production of enzyme inhibitors. Liposomes rapidly became localized in lysosomes subsequent to endocytosis by macrophages. Morphologic evidence suggested that secondary lysosomes containing liposomal residues then fused with the parasitophorous vacuole. Aspects of one possible pathway are discussed which may account for the greatly enhanced effectiveness of liposomal chemotherapy for experimental visceral leishmaniasis.

The American leishmaniases: some observations on their ecology and epidemiology

As the first species of Leishmania encountered were the agents of human visceral and cutaneous leishmaniasis, it is understandable that studies on these parasites for a long time concentrated on those organisms commonly causing disease in man. Epidemiological studies over the past 20 years or so, however, have led to the inescapable conclusion that the genus Leishmania is comprised of numerous species of well adapted parasites, in a wide range of mammals, throughout most of those tropical and subtropical regions of the world where phlebotomine sandflies exist (Diptera: Psychodidae). Many of the leishmanias probably never gain entrance into man: due either to an incapacity to survive in his tissues, or (more likely) because the natural sandfly vectors do not feed on him. The leishmanias that do infect man are, nevertheless, among the greatest protozoological scourges of mankind, and a better understanding of their life-cycles may well help in future prevention or control of the diseases they cause. With few exceptions the leishmaniases are zoonoses, with a major source of infection in wild or domestic animals. In the Americas, the disease is essentially a rural one, and most commonly acquired by those penetrating forested or wooded regions. The following paper deals with the better known human leishmaniases of the New World, and some new ones, and discusses the major historical events in the laborious task of elucidating their ecology and epidemiology.

Protective effect of glucan against visceral leishmaniasis in hamsters

The effect of pre- or posttreatment with glucan, a reticuloendothelial stimulant, on the course of Leishmania donovani infection was assessed in highly susceptible hamsters. Intravenous administration of glucan before or after L. donovani infection significantly suppressed proliferation of amastigote-stage parasites in liver and spleen. Glucan-activated peritoneal macrophages in vitro also significantly reduced multiplication of the intracellular parasite. Ultrastructural studies revealed a well-defined hepatic granulomatous response to glucan, with hypertrophic Kupffer cells and reduced numbers of intracellular parasites compared to the control group. In additional studies, groups of hamsters were immunized by intravenous injections of glucan with Formalin-killed promastigote-stage L. donovani cells and challenged 60 days after the last immunizing injection. This treatment regimen significantly prolonged the mean survival time of those hamsters which died after infection, relative to untreated control groups. Hamsters stimulated with the glucan-killed promastigote preparation also exhibited significant reductions in splenic amastigotes on days 10 and 21 postinfection compared with all other control groups, but on day 35, splenic amastigotes did not differ significantly from those of control animals. Our composite observations provide evidence for glucan-enhanced nonspecific resistance of hamsters to visceral leishmaniasis.

Ultrastructure of amastigotes of Leishmania donovani in the bone marrow of a dog

Visceral leishmaniasis was diagnosed in a dog which had been in Spain for 4 years before being brought to Florida. A bone marrow aspirate from the dog was examined by electron microscopy. Phagocytized amastigotes by macrophages had an electron-dense plasma membrane and contained ribosomes, rough endoplasmic reticulum, a well-developed Golgi apparatus, an intracellular flagellum, lipid, a kinetoplast, a row of microtubules immediately beneath the cell membrane, and a nucleus with marginated chromatin. Mean diameter and microtubule number of the dog isolate were similar to those reported for Leishmania donovani amastigotes of human origin. Plasma cells were congregated in the vicinity of parasitized macrophages.

Cell surface origin of antigens shed by Leishmania donovani during growth in axenic culture

Antisera against isolated cell surface preparations (PCSP-As) of Leishmania donovani promastigotes were used to detect extracellular antigens produced during the growth of these organisms in four different growth media. The PCSP-As precipitated two major antigenically identical but electrophoretically distinct components, in addition to several minor antigens. Immunoelectrophoretic studies employing PCSP-As, PCSP-As absorbed with intact, live promastigotes, and PCSP-As absorbed with a major extracellular antigen demonstrated the antigenic identity between the major extracellular antigens and two major components externally disposed at the surface of promastigotes. Growth curve kinetic investigations suggested that the major extracellular antigens did not appear in the growth media primarily as a result of cell lysis or damage. The carbohydrate nature of the major extracellular antigens was indicated by physicochemical characterization.

A role for oxygen-dependent mechanisms in killing of Leishmania donovani tissue forms by activated macrophages

Leishmania donovani, the causative agent of visceral leishmaniasis, infects macrophages (M phi ) of susceptible vertebrates. Immunologically activated M phi are leishmanicidal, but the mechanisms involved in the killing process are not well defined. We sought to investigate the role of reactive oxygen intermediates in the killing of L. donovani. Both the free-swimming promastigote and the intracellular amastigote forms were found to be susceptible to killing in vitro by hydrogen peroxide and other oxygen intermediates. Upon phagocytosis by mouse peritoneal M phi, promastigotes elicited a significantly stronger respiratory burst compared with amastigotes as measured by release of superoxide anion. Although amastigotes do not elicit a strong burst of M phi oxidative metabolism during the initial phagocytic event, immunologically activated M phi that acquired leishmanicidal capacity could be triggered to release substantial amounts of H2O2. Hence, the development of leishmanicidal capacity was correlated temporally with enhanced H2O2 generation by the M phi. In contrast, M phi that lost their ability to release significant amounts of H2O2 after several days in culture were unable to eliminate their parasite burden. Catalase markedly inhibited the elimination of amastigotes by lymphokine-stimulated M phi. In toto, the results implicate reactive oxygen intermediates in killing of the tissue form of L. donovani by its host cell, the mononuclear phagocyte.

[The diagnostic value of lectins for the epidemiology of Chagas' disease and the differentiation of Leishmania from the Old and New World]

An interspecific differentiation between T. cruzi, T. rangeli and T. conorhini can be done with the lectin II from the marine sponge Aaptos papillata. Independently from the origin the T. cruzi strains can intraspecifically subdivided into two strain-groups from WGA-type and PNA-type. The Leishmania strains from the Old World can inter- and intraspecifically distinguished by lectins while the strains from the New World form only two groups. A comparison of the agglutination-behaviour of the Leishmania parasites shows that strains of L. m. mexicana, L. b. braziliensis, L. aethiopica and L. m. amazonensis belong to the same type. The second agglutination-type includes strains of L. t. major (Near East), L. m. amazonensis and L. m. pifanoi.

Kala-azar in Portugal. I. Attempts to find a wild reservoir

Kala-azar is now increasing in Portugal where it has been known since 1910. The natural region studied is made up of the western basins of the Tejo and Sado rivers with their important estuaries and the area south of Lisbon. The climate and vegetation are mainly of the mediterranean type. Kala-azar has always been endemic in the sub-region southwest of Lisbon (45 cases from 1961 to 1978). In the Setubal peninsula the disease has always had a low incidence (10 cases from 1961 to 1978). The Alcácer do Sal subregion was, in the past, the second most active endemic zones in the country although after 1950 there was a sudden fall in prevalence (only two cases reported from 1961 to 1978). In this natural region foxes (Vulpes vulpes silacea Miller, 1907) are abundant. One-hundred and ninety-eight foxes, mostly from the Alcácer do Sal region, were killed and studied using direct examination of spleen and liver, culture in NNN of spleen and bone-marrow, hamster inoculation of spleen and IFAT of serum. All the examinations were negative for Leishmania, while Hepatozoon was found in 40.6% of the foxes and filaria in 11.9%. In spite of some shortcomings of the study methods it is suggested that they may not be an autonomous sylvatic cycle of kala-azar. The negativity of the results, lack of any sporadic cases in rural people and absence of the characteristics of a natural reservoir in the foxes, all seem to point to such a conclusion.

Susceptibility of clinically sensitive and resistant Leishmania to pentavalent antimony in vitro

Standard courses of pentavalent antimonials frequently fail to cure cutaneous, mucocutaneous, and visceral leishmaniasis, and characteristically fail to cure diffuse cutaneous disease. We have determined the in vitro sensitivity of clinical isolates of Leishmania to pentavalent antimony to determine if inherent drug resistance of the parasite is responsible for treatment failures in human beings. Intracellular amastigotes resulting from promastigote-initiated infection of human macrophages were exposed to pentavalent antimony for 6 days at 34.5-35 degrees C. Amastigotes from clinically sensitive simple cutaneous lesions exhibited a range of in vitro sensitivity. Four strains were greater than or equal to 90% eliminated and two strains were 70-75% eliminated in vitro by concentrations of antimony (15-20 micrograms Sb/ml), comparable to peak achievable serum levels in humans. Amastigotes from initially clinically resistant simple cutaneous lesions showed a wider range of sensitivities. Five strains were greater than or equal to 90% eliminated, but one strain was only 40% eliminated and another strain was completely insensitive in vitro. The clinically resistant diffuse cutaneous strain was 61% eliminated. The techniques described herein permit determination of the in vitro antimicrobial susceptibility of Leishmania from all major human forms of leishmaniasis. The data from this series indicate that in a minority of initially resistant cases parasite resistance to the drug may be contributing to clinical resistance, and use of non-antimonial drugs might be recommended for future therapy.

In vitro induction of intracellular killing of parasitic protozoa by macrophages

Macrophages play an important role in the defence of the host against infection by certain parasitic protozoa. Aspects of the interaction in vitro between macrophages and Trypanosoma cruzi, Toxoplasma gondii, and Leishmania spp. are reviewed. These three types of parasites are internalized by phagocytosis; the relationship established between the parasites and intracellular organelles vary, however. Whereas T. cruzi appears to escape from the phagocytic vacuole, T. gondii inhibits phagosome-lysosome fusion, and Leishmania proliferates within the phagolysosomal environment. Macrophages can be activated in vitro, by incubation with lymphokine-rich media, to kill these parasites. Destruction of these microorganisms requires that an adequate supply of oxygen metabolites be produced. Variations in the levels of endogenous scavengers of such metabolites in both macrophages and parasites may explain differences in the susceptibility of parasites to killing by activated macrophages.

Leishmaniasis in Brazil: XVIII. Further evidence incriminating the fox Cerdocyon thous (L) as a reservoir of Amazonian visceral leishmaniasis

Major endemic areas of visceral leishmaniasis in Brazil are located in the drier, poorly forested regions, principally in the northeastern States such as Ceará and Bahia. Cases of the human disease in the Amazon Region are rare, very sporadic, and seldom present opportunities for epidemiological study. Following the report of a fatal case near Salvaterra, the Island of Marajó, Pará State, a preliminary investigation has resulted in the isolation of a parasite regarded as Leishmania donovani chagasi from the viscera and skin of an apparently healthy fox, Cerdocyon thous, captured in the same locality. This represents the third recorded isolation of the parasite from this species of fox in the Amazon Region. The inapparent nature of the infections supports the suggestion that this canid may represent the primitive natural host of L. d. chagasi. C. thous is commonly associated with forested or wooded areas, and enzymic profiles for the enzymes ASAT, ALAT, PGM, GPI, MDH, MPI, G6PD, PEP and ACP failed to distinguish an isolate of L. d. chagasi from this animal in Pará from others obtained from cases of human visceral leishmaniasis in the neighbouring States of Maranhão, Ceará and Bahia. This suggests that the major, present-day endemics may have originated from a primary silvatic enzootic.

[Post kala-azar dermal leishmaniasis and "crithidia" serology (author's transl)]

A case of visceral leishmaniosis in a three year old child is reported. The rarity of post kala-azar dermal leishmaniosis and the diagnostic value of "Crithidia" serology are discussed.

A review of kala-azar in China from 1949 to 1959

This is the first account of China as an important area of kala-azar to appear in the west for nearly 50 years. The review is divided into four main sections. The epidemiological aspects which are described include the geographical distribution and endemicity (under the sub-headings natural conditions of the epidemic area, age distribution, sex differences, seasonal changes in incidence) and research on reservoirs (under the sub-headings survey of canine leishmaniasis and survey of other wild and domestic animals). The section on clinical aspects covers symptoms and signs, post kala-azar dermal leishmaniasis, laboratory diagnosis (puncture, serum tests, complement fixation test, intradermal test) and treatment (medication and the effects of treatment). The possibility that two different types of kala-azar occur in China is discussed and the paper concludes with an appraisal of the present position.