The brain as a source of relapsing Trypanosoma brucei infection in mice after chemotherapy

Response of Trypanosoma congolense in goats to single and double treatment with diminazene aceturate

Diminazene aceturate is one of a limited number of compounds currently marketed for treatment of trypanosomiasis in cattle, sheep and goats. The pharmacokinetics of the compound in goats suggest that double treatment with diminazene aceturate might enhance the compound's therapeutic activity. A study was therefore conducted in goats using two clones of Trypanosoma congolense, IL 3274 and IL 1180, which were previously shown to be resistant and sensitive, respectively, to single treatment with diminazene aceturate. The results indicated that, as compared to single treatment, double treatment with diminazene aceturate at a dose of 7.2 mg kg-1 bodyweight, at either eight or 24 hour intervals, did not greatly enhance the therapeutic activity of the drug. Furthermore, treatment with the same drug dose eliminated infections with T congolense IL 3274 when treatment was administered 24 hours after infected Glossina morsitans centralis had fed, but failed to do so if treatment was delayed until after goats were detected to be parasitaemic. This suggests that failure of T congolense IL 3274 to respond to treatment with diminazene may not be due to drug resistance per se.

Pathology of experimental Trypanosoma evansi infection in rabbits

Histopathological examination of tissue sections from the organs of rabbits experimentally infected with Trypanosoma evansi revealed evidence of a vigorous immunological response. Changes in the spleen, lymph nodes, vulva, eyelids and ears indicated a protective immune response, but changes in the kidneys, lungs and heart were destructive in nature and capable of causing sudden death of the host. Hepatic damage capable of interfering with the host's immune response was also observed. The presence of many parasites in the vulval tissue calls for further investigation into the possibility of sexual transmission of T. evansi.

In vivo assessment of drug sensitivity of African trypanosomes using the akinetoplastic induction test

Following treatment of mice infected with Trypanosoma congolense or T brucei brucei with various doses of isometamidium chloride or diminazene aceturate, the induction of akinetoplastic (AK) forms was observed in the trypomastigotes of both species within 10 hours of drug administration. The levels of AK-induction were closely correlated with the levels of resistance to each compound found using a standard in vivo drug assay in mice. In general, ineffective doses of either compound conferred AK-induction rates of less than 30 per cent; relapsing cases had between 30 and 50 per cent while curative doses had AK-induction rates of 50 per cent or more. In vivo determination of AK-induction rates using ordinary light microscopy is thus a potentially feasible alternative indicator to the conventional use of mice infection and treatment methods for assessing drug sensitivity in African trypanosomes.

Trypanosoma congolense: the in vitro akinetoplastic induction sensitivity assay

Incubation of Trypanosoma congolense in diminazene aceturate (Berenil) or isometamidium chloride (Samorin) induced akinetoplastic (AK) forms in vitro. The AK values (expressed in percent) obtained were found to be useful for rapid assessment of relative drug sensitivities. In susceptible clones, AK forms were induced at all drug concentrations tested, whereas in resistant clones they were induced only at higher concentrations. The Berenil-resistant clone exhibited AK values of 0.9% +/- 0.6%--8.9 +/- 2% at concentrations of 1-100 micrograms/ml at 4-10 h post-inoculation (p.i.), whereas the Berenil-susceptible clone displayed values of 9.3% +/- 13%--19.2% +/- 5% at 0.1-50 micrograms/ml. Motile trypanosomes were not seen at 100 micrograms/ml at 4 h p.i. or at 10 or 50 micrograms/ml at 10 h p.i. The Samorin-resistant clone showed AK values of 0.5% +/- 0.1%--43% +/- 3% at concentrations of 0.1-100 micrograms/ml at 4 and 10 h p.i., whereas the Samorin-susceptible clone exhibited values of 5.3% +/- 2%--45% +/- 4% at 0.0005-100 micrograms/ml. These results were supported by the findings obtained using a mouse infectivity test.

Future prospects for the chemotherapy of human trypanosomiasis. 2. Combination chemotherapy and African trypanosomiasis

This paper reviews the progress which has been achieved with combination chemotherapy of experimental murine central nervous system trypanosomiasis. Successful treatments have been achieved with suramin followed by 5-nitroimidazoles; difluoromethylornithine in combination with bleomycin, 9-deazainosine, suramin, arsenicals, antimonials and diamidines; and also the arsenicals in combination with the 5-nitroimidazoles or nifurtimox. Pretreatment with prednisolone and azathioprine, to minimize reactive encephalopathies, and supportive treatment with oxygen are both indicated.

Differential susceptibility to DL-alpha-difluoromethylornithine in clinical isolates of Trypanosoma brucei rhodesiense

DL-alpha-Difluoromethylornithine is an enzyme-activated inhibitor of ornithine decarboxylase and an antagonist of polyamine metabolism that has been successful in clinical trials against West African sleeping sickness caused by Trypanosoma brucei gambiense. Its potential for use against the more virulent East African form of the disease, caused by T. brucei rhodesiense, is not certain. We examined 14 East African clinical isolates from the Kenya Trypanosomiasis Research Institute strain bank plus 2 established isolates for susceptibility to DL-alpha-difluoromethylornithine and to standard trypanocides. Seven of 16 strains were partially or totally refractory to DL-alpha-difluoromethylornithine in our test system. Four strains were also refractory to arsenical drugs, and five were refractory to diamidines. The results indicate that other novel agents or combinations of established agents may be needed for chemotherapy of East African disease.

Chemotherapeutic effects of Annona senegalensis in Trypanosoma brucei brucei

Mice infected with Trypanosoma brucei brucei 8/18 strain were treated orally and intramuscularly (im) with aqueous root extracts of Annona senegalensis, in doses of 27.8 mg kg-1 and 9.5 mg kg-1 respectively, for four consecutive days commencing 72 hours after the mice were infected. At these dosages the parasites were cleared from the circulation and no relapse was recorded over 60 days. The plant extract, however, had no effect on the trypanosomes when therapy was initiated at the late stages of infection, that is, about the sixth day when the parasitaemia level was 0.9 x 10(6); and all the animals died a day or two later. The herbal extracts also did not show any prophylactic action when given prior to infection. The root extract possesses different margins of safety in the mice depending on the route of administration. The therapeutic index for oral administration was 5.13, and that for im administration was 1.8. Chemical tests revealed that the plant extract contains alkaloids, saponins and tannins. Adverse reactions, especially to doses of 2.3-5.76 mg kg-1, were noted in animals that received the drug parenterally, but not when the drug was administered orally. However, A. senegalensis is shown to be therapeutically effective against T. b. brucei in mice, which agrees with the claims of Nigerian practitioners of Traditional Medicine that it is effective against trypanosomiasis in man.

Neurobiology of sleeping sickness

The advanced stages of sleeping sickness are correlated with a spread of trypanosomes into the central nervous system (CNS), producing a disseminated encephalitis. Inflammatory reactions extend along the blood vessels causing perivascular cuffing, which consists of in filtrations and proliferations of lymphocytes and also increased numbers of astrocytes and microglia. Progress in our understanding of the functions of astrocytes suggests that they are efficient antigen-presenting cells, initiating and regulating the intracerebral inflammatory response and limiting parasite spread to the perivascular spaces.

Neurochemical measurements in the brains of mice infected with Trypanosoma brucei brucei (TREU 667)

Trypanosoma brucei brucei (TREU 667) infected mice were used as a model of African trypanosomiasis, a disease in which neuropsychiatric manifestations occur. To study the possible neurochemical basis of these abnormalities, we measured brain acetylcholine receptor numbers, activities of the cholinergic enzymes, choline acetyltransferase (CAT), and acetylcholinesterase (AChE), and regional concentrations of the monoamines, dopamine (DA), serotonin (5-HT), and norepinephrine (NE), and their acid metabolites, homovanillic acid (HVA), 3,4-dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) in mice infected with T. b. brucei. There were no significant changes in CAT or AChE activities or acetylcholine receptor numbers at either 35 or 50 days post-infection (PI). At day 35 PI, the only significant finding was a decrease in 5-HIAA concentration in the brain stem, a change which did not persist to day 50 PI. At day 50 PI there were, however, significant increases in DA concentration in the brain stem and NE concentrations in the hippocampus, cerebellum, brain stem and striatum. To establish a chronic relapsing murine model, mice were treated with diminazene aceturate (Berenil) at day 60 PI and killed 60 days later (120 days PI). In these mice, 5-HT concentrations were significantly increased in the hypothalamus and decreased in the cortex. In addition, 5-HIAA concentrations were increased in the striatum and hypothalamus and HVA concentrations were increased in the striatum and hippocampus. Our data, taken together with that of others, suggests that there are alterations in the monoaminergic, but not in the cholinergic, neuronal system, in African trypanosomiasis. These data may form the basis for the neuropsychiatric abnormalities that are associated with this disease.

Recent studies of the biology of Trypanosoma vivax

Recent biological investigations of the African trypanosomes have been moving away from their previous preoccupation with the phenomenon of antigenic variation. The feeling has arisen that antigenic variation, as demonstrated by the Trypanozoon and Nannomonas subgenera of trypanosomes, is too extensive, the number of serodemes too large and the coexistence of different species in many areas too complicated, to allow any immunoprophylaxis based on antibodies to variable antigens. This is, of course, not to rule out possible biochemical intervention in the biosynthesis or export of VSG molecules by trypanosomes. However, in the case of T. vivax, more information is required concerning antigenic variation and coat structure in this organism before these avenues of investigation are discarded. Ways of improving the yield of mature metacyclic trypanosomes in vitro must be found, so that the contribution of metacyclic variable antigens to the induction of immunity in T. vivax infection can be elucidated. The number of bloodstream VATs must be determined (perhaps by genetic rather than serological means), as there is evidence both for VAT exhaustion contributing to the self-cure of infected hosts, and for a possible limit to the number of VATs which can be expressed in infections in Africa. In South America nothing is known of the number of serodemes of T. vivax which exist, although such knowledge is obviously required, especially if immunity to bloodstream variants is the more important mechanism of inducing immunity to this trypanosome and true cyclical transmission is rare in, or absent from, that subcontinent. Further, in a fragile organism, with a coat of suspect integrity, the method of VSG packing and the relative exposure of underlying surface molecules seems to hold out even more hope for an immunological intervention based on cell surface but invariant molecules than is the case with T. brucei or T. congolense, although this is being attempted with the latter species. In T. brucei infections the appearance of the non-dividing stumpy population acts as a stimulus to the induction of humoral immune responses. In ruminants, antibody responses to T. vivax, at least as judged from lysis tests, lag behind the appearance of the different VATs by some days. It would be important to determine, therefore, whether, if late bloodstream forms could be induced more frequently in the ruminant, the speed of anti-VAT responses could be enhanced. Whilst self-cure appears to be relatively common in T. vivax infections, it is unlikely that it results in sterile immunity.(ABSTRACT TRUNCATED AT 400 WORDS)

Extravascular foci of Trypanosoma vivax in goats: the central nervous system and aqueous humor of the eye as potential sources of relapse infections after chemotherapy

Relapse of parasitaemia after drug treatment of trypanosome infection is normally attributed to drug-resistance on the part of the parasite, under-dosage of the drug or reinfection of the host. In addition, inaccessibility of parasites to drug through sequestration in privileged extravascular sites has been shown in the past to occur with Trypanosoma brucei, and we have obtained evidence that extravascular foci of T. vivax can also serve as a source of relapsing infections. Infection of goats with a West African stock of T. vivax resulted in severe illness, which was fatal if untreated. During the terminal stage of an acute infection, clinical signs of central nervous system involvement were apparent. Histologically, the choroid plexus was swollen and oedematous, and in some cases meningitis or meningoencephalitis was seen. Trypanosomes could be detected in the cerebrospinal fluid, and also extravascularly in the choroid plexus and meninges. In three cases they were present in the aqueous humor, associated with corneal cloudiness or opacity. Treatment of 2 goats with the trypanocidal drug diminazene aceturate eliminated parasitaemia, but infections in both relapsed about 6 weeks later, despite trypanosomes being undetectable in the bloodstream during the intervening period. We conclude that the relapse infections were caused by reemergence of trypanosomes from the CNS and/or the eye, where sequestered parasites may have been inaccessible to the trypanocide.

Relapses in dogs experimentally infected with Trypanosoma brucei and treated with diminazene aceturate or isometamidium chloride

Twenty dogs of mixed local East African breeds were used. Five of the dogs were uninfected controls and 15 were infected with T. brucei (ILRAD 273). Five of the infected dogs were untreated controls, five were treated with a high curative dose of diminazene aceturate, (7 mg kg-1 body weight (wt.), and five were given a subcurative dose of isometamidium chloride (1 mg kg-1 body wt.). The drugs, given at 8 days post infection (d.p.i..), led to apparent recovery. The antibody titres, however, remained high in both groups and at 42-49 d.p.i. there was at least one relapse in each treatment group. Parasite populations from relapsed animals were more resistant to the drugs than the original infecting populations. The implications of these findings are discussed.

Development of Trypanosoma brucei in suckling mouse brain following intracerebral injection

Intracerebral inoculation of Trypanosoma b. brucei and T. b. rhodesiense into suckling mice produced infection of brain tissue which subsequently gave rise to an infection of the blood and other tissues, in which a normal histopathological picture was observed. Treatment of other intracerebrally infected sucklings with 5 mg/kg diminazene aceturate (Berenil) to clear the infection from the blood permitted a study of the course of the infection in the brain without interference from pathological processes induced by bloodstream infections. There was rapid multiplication and migration of trypanosomes throughout the brain of mice. Pathological processes normally seen in experimental central nervous system infections were absent, except in a single mouse treated earlier with Berenil which developed meningo-encephalitis with trypanosomes present in the choroid plexus. The possible use of such a model system in chemotherapeutic studies is discussed.

African trypanosomiasis: haematogenic brain parasitism early in experimental infection through bypassing the blood-brain barrier, with considerations on brain trypanosomiasis in man

A hematogenic invasion of the brain in suckling NMRI mice infected with Trypanosoma brucei rhodesiense was initiated by means of a mechanical damage of the blood-brain barrier. The brain was punctured after development of a blood infection. Brain infection was found in 31 out of 32 animals examined. Trypanosomes are initially capable of rapid multiplication. The number of parasites was highest during the 1st week. From the middle of the 2nd week the number of parasites decreased continuously, alongside increasing atrophy. In the 3rd and 4th week only rare degenerating or ghost trypanosomes were present. No reactions were detected in the glial and mesenchymal cells. It is presumed that the short phase of trypanosome multiplication is due to the temporary collateral oedema of the brain tissue. The decrease in parasites from the 2nd week onwards is mainly attributed to natural death due to particular anatomical features of the brain tissue. These are also responsible for the absence of defensive inflammatory reactions, based on the hypothesis that contact between trypanosomes and the cells of the brain blood vessels is prevented.

Trypanosoma brucei and T. vivax: salicylhydroxamic acid and glycerol treatment of acute and chronically infected rats

In rats infected with monomorphic Trypanosoma brucei brucei, the efficacy of the therapy with salicylhydroxamic acid plus glycerol, i.e., combined therapy, decreased with increasing time after infection. It failed completely after the infection was made chronic by suboptimal treatment for 6 weeks. When this chronic infection had been established and "optimal" treatment was given, viable trypanosomes could still be detected 1 day later in brain and muscle but not in blood. In most organs, the concentrations of salicylhydroxamic acid and glycerol were lower than in the blood plasma; the maximum concentration of glycerol in the brain was only 20% of that in plasma. The most likely explanation for the failure of the combined therapy is that, in certain tissues, the concentration of the drugs remains too low to kill extravascular trypanosomes. Other explanations, such as the selection of a resistant strain or the survival of (extravascular) forms with a more active mitochondrion, could be excluded with a high degree of probability. Suramin was very effective, even after combined therapy had failed repeatedly, while melarsoprol was less effective. As in combined therapy, the dose of melarsoprol that could cure an acute infection was insufficient to cure a chronic infection. Combined therapy failed after a spontaneous chronic infection with T. b. rhodesiense had existed for 5-7 weeks, but it was effective in T. vivax infected rats even when parasitemia had been present for at least 4 days. Effective alternative schedules for combined therapy were not found.

Relapse infection after chemotherapy in goats experimentally infected with Trypanosoma brucei: pathological changes in central nervous system

Fourteen goats were experimentally infected with Trypanosoma brucei with the following results: Four animals became terminally ill 24 to 47 days after inoculation of trypanosomes and were killed for necropsy. A second group of four goats became sick, had signs of systemic trypanosomiasis, were treated with diminazine aceturate (Berenil) and recovered showing no signs of disease over observation periods of 151 to 163 days. A third group of six goats, were treated with Berenil and temporarily recovered and in 60 to 79 days after therapy; four of these goats underwent relapse infection characterized by severe central nervous system (CNS) disease. Two of these goats were necropsied 45 days after chemotherapy, before clinical signs were evident, to show early neurological lesions. In group 3 (the relapse group), the microscopic changes became more severe as relapse infection progressed. Microscopically, the central nervous system lesions were edema, hyperemia, and infiltration of plasma cells, small lymphocytes, and some macrophages in the leptomeninges, choroid plexus, and brain parenchyma. Relapse infection is discussed from the standpoint of an occult phase of the disease where parasites are protected from the effects of trypanocidal drugs by the blood-brain barrier.

The trypanocidal effect of drugs in different parts of the brain

Three parts of the brain, cerebral cortex, lining of ventricle and choroid plexus, are cleared of trypanosomes to different extents by different drugs. There appear to be several barriers preventing drugs from acting in different parts of the brain, the concept of a single "blood-brain barrier" does not account for the phenomena observed. The protection of trypanosomes from certain drugs by the choroid plexus and ventricular wall supports the concept of an intracellular stage of Trypanosoma brucei in the ependymal cell; this concept is also supported by differences in parasitaemia resulting from the inoculation of ependymal and of other tissues. Alternative therapies for sleeping sickness are suggested, one of which (suramin/metronidazole) is being advanced for trials in man.

Similarity in variable antigen type composition of Trypanosoma brucei rhodesiense populations in different sites within the mouse host

Trypanosoma brucei rhodesiense subpopulations in different sites within the body of infected mice were isolated and enumerated on day 6 of cyclically transmitted infections. Most trypanosomes were in the blood vasculature and spleen but approximately 6% occurred in lymph nodes and about 9% were extravascular. Most of the extravascular trypanosomes were in the peritoneal and pleural cavities; significant numbers also occurred in the brain and kidneys. Six major variable antigen types (VATs) were detected by immunofluorescence using specific antisera and monoclonal antibodies. The prevalence of each VAT was essentially the same in subpopulations in the blood, mesenteric and inguinal lymph nodes, brain, kidneys and peritoneal and pleural cavities. This similarity of VAT composition in different subpopulations is probably caused by high rates of dynamic interchange of trypanosomes between sites. Extravascular trypanosomes, therefore, form a significant proportion of the total population in acute infections of mice but they do not appear to play any special role in the population biology of antigenic variation at this stage of infection.

Induction of human serum-sensitive Trypanosoma brucei stabilates into human serum-resistant "T. rhodesiense"

When chronic Trypanosoma brucei infections of mice are treated with 20 mg/kg suramin, those trypanosomes which have escaped chemotherapy because they are residing in the brain, exhibit a higher degree of human serum resistance than the original infection. This resistance increases if the chronic infection is retreated for a second time, before the trypanosomes in the brain are tested by the blood incubation infectivity test. The transformation is not due to a selection of T. rhodesiense from a T. brucei/T. rhodesiense mixture in the original stabilates as cloned derivatives also exhibit these same characteristics. The implications of this finding are discussed.

Immunopathological aspects of trypanosomal meningoencephalitis in vervet monkeys after relapse following Berenil treatment

Four quarantined vervet monkeys were treated with intramuscular Berenil in patent CNS infection after experimental trypanosome inoculation with Trypanosoma brucei rhodesiense or T. brucei brucei. All four animals relapsed in the post-therapeutic survival time of 37 to 209 days when they had fully developed meningoencephalitis in histological sections with the presence of interstitial intracerebral trypanosomes, which were confirmed in two monkeys by electron microscopy. In both, sequential samples of the serum and cerebrospinal fluid were analysed for circulating immune complexes, immunoglobulins and albumin. From these results the intracerebral IgG synthesis and the impairment of the blood-brain-barrier were calculated, both being present in advanced infection. Circulating immune complexes were present in the serum, but could not be demonstrated in the cerebrospinal fluid. The monkey model therefore permits the study of various aspects of cerebral trypanosomiasis. Berenil treatment is inefficient in patent CNS infection and leads to a protracted, less virulent disease course with terminal meningoencephalitis and intracerebral "persister" trypanosomes. This drug-induced trypanosome shift with meningoencephalitis could be used for chemotherapeutic purposes to test new compounds in late stage disease.

The use of 2-substituted 5-nitroimidazoles in the treatment of chronic murine Trypanosoma brucei infections with central nervous system involvement

Chronic infections of Trypanosoma brucei GVR 35/2 in mice, normally relapse after conventional chemotherapy because infective trypanosomes in the brain escape the action of the drug and are able to multiply and eventually re-establish a parasitaemia. However, if treatment consists of a single dose of 1 x 20 mg/kg suramin followed 3 or 4 days later by a 2-substituted 5-nitroimidazole, given intraperitoneally, either as a single dose or as a course of daily injections, relapses rarely occur and the majority of the mice are permanently cured. The minimum effective levels for the three 5-nitroimidazole compounds (Merck Sharp and Dohme, Rahway, NJ, USA) were two doses of 10 mg/kg of L611,744; four doses of 10 mg/kg of MK 436; and three doses of 10 mg/kg of L634,549. Generally it was more effective to divide a given total dose into two or more daily doses, rather than to give the 4-nitroimidazole as a single treatment. The effective dose levels are low enough to be of practical significance and, if the 5-nitroimidazoles were ever licensed for humans, might well prove to be an alternative to melarsoprol treatment for the elimination of trypanosomes from the central nervous system.

Efficacy of combinations of difluoromethylornithine and bleomycin in a mouse model of central nervous system African trypanosomiasis

DL-alpha-Difluoromethylornithine, a polyamine biosynthesis inhibitor, and bleomycin, a currently used antineoplastic agent, have each previously been shown to be curative for acute short-term infections of mice with Trypanosoma brucei brucei, an African trypanosome closely related to those that cause the human disease African sleeping sickness. These agents were tested singly and in combination in a previously described mouse model of sleeping sickness with demonstrable brain involvement. The original model is extended by using two additional strains of outbred mice and by demonstrating that melarsoprol, an arsenical and currently the only drug used for human African trypanosomiasis involving the brain, was also curative for these brain infections. Neither difluoromethylornithine nor bleomycin alone was curative for the brain infections; however, many combinations of the two drugs were found to be 100% curative with no evidence of immediate toxicity.

Treatment with suramin and 2-substituted 5-nitroimidazoles of chronic murine Trypanosoma brucei infections with central nervous system involvement

Mice infected with either of two isolates of Trypanosoma brucei, GVR 23/1 or GVR 35/1, develop a chronic infection in which trypanosomes are localized in the central nervous system. These infected mice were used to evaluate the efficacy of a combination drug treatment comprising suramin and one of three 2-substituted 5-nitroimidazoles. None of the three 5-nitroimidazoles tested alone, cured mice when administered 21 days after infection. However, it was found that T. brucei GVR 23/1 infections could be cured by a single dose of 20 mg/kg suramin followed by a single dose of 80 mg/kg L611,744 [3a,4,5,6,7,8,9,9a-octahydro-3-(1-methyl-5-nitroimidazol-2yl)cycloocta(D) isoxazole]. The single dose of 20 mg/kg suramin had to be followed by four doses of 80 mg/kg L611,744 to cure mice infected with another stabilate, T. brucei GVR 35/1. A single dose of 20 mg/kg suramin followed either by four doses of 250 mg/kg MK 436 [3a,4,5,6,7,7a-hexahydro-3-(1-methyl-5nitro-1H-imidazol-2-yl)-1, 2-benzisoxazole] or four doses of 70 mg/kg of a dihydroxy analogue of MK 436 [cis-3a,4,5,6,7,7a-hexahydro-3-(1-methyl-5-nitro-1H-imidazol-2-yl)-1, 2-benzisoxazole-6,7-diol] also permanently cured all T. brucei GVR 35/1.

Cryptic stage of sleeping-sickness trypanosome developing in choroid plexus epithelial cells

Electronmicrographs of the choroid plexus from rats infected with Trypanosoma brucei rhodesiense showed that trypomastigotes from the perivascular spaces may penetrate and undergo multiple division in the ependymal cells which locally constitute the blood-brain barrier. Progressive degeneration of the ependymal cell liberates trypomastigotes back into the perivascular space, from which re-entry into the blood may occur. Re-entry to the blood does not take place from any tissues other than the brain and its membranes. These findings suggest that the ependymal cells of the choroid plexus are the site of the cryptic stage of the sleeping-sickness trypanosome.

Relapse of monomorphic and pleomorphic Trypanosoma brucei infections in the mouse after chemotherapy

Infections in mice were initiated with trypomastigotes from two lines of Trypanosoma brucei derived from the same primary isolated. Infections with one line were initiated by inoculation of metacyclic trypomastigotes from infected tsetse flies and the resulting infections were pleomorphic. The other line had been passaged 32 times in rodents and inoculation of bloodstream trypomastigotes gave rise to monomorphic infections. In both infections there were high levels of parasitaemia until death up to 4 weeks later if the infection was untreated. It was shown that after chemotherapy with 40 mg/kg diminazene aceturate (Berenil) relapses occurred in both types of infection after an aparasitaemic period of 2--3 weeks. Further, it was shown that 3 days after chemotherapy, brain tissue but neither spleen, liver nor blood was capable of transferring infection to normal recipient mice. There were two major differences in the response of the two infections to chemotherapy. First, treatment of the pleomorphic infection as soon as day 6 after infection resulted in a subsequent relapse while the monomorphic infection had to be at least 12 days old at the time of treatment before occurred. Second, following treatment of the pleomorphic, but not of the monomorphic infection there was an early transient recrudescence of low numbers of trypanosomes which were found to be non-infective to recipient mice. The early transient relapse was followed by a further aparasitaemic period and then the late continuous relapse characterised by large numbers of infective trypanosomes.

Inhibition of glutathione synthesis as a chemotherapeutic strategy for trypanosomiasis

With the expectation that trypanosomal glutathione (GSH) plays a major protective role against the endogenous oxidant stress that results form high intracellular levels of H2O2, we sought to deplete Trypanosoma brucei brucei of their GSH through inhibition of its biosynthesis. Administration of buthionine sulfoximine (BSO), a reversible inhibitor of gamma-glutamylcysteine synthetase, to parasitemic mice resulted in a progressive decrease in trypanosome GSH content, such that parasites isolated after 5 h or BSO treatment contained 50% of normal values. When BSO administration was continued for 18 h (intraperitoneal injection of 4 mmol/kg every 1.5 h), parasitemias temporarily cleared. When inhibitory plasma levels of BSO were maintained for about 27 h, two out of six infected mice were cured and the rest had significantly prolonged survival. These findings demonstrate the potential value of GSH depletion for the treatment of trypanosomiasis.

Polyamine metabolism: a potential therapeutic target in trypanosomes

alpha-Difluoromethylornithine (RMI 71,782), a specific irreversible inhibitor of the first step in polyamine biosynthesis, that is, the formation of putrescine from ornithine by ornithine decarboxylase, cures mice infected with a virulent, rodent-passaged strain of Trypanosoma brucei brucei. This parasite is closely related to the trypanosomes that cause human sleeping sickness. The drug, which is remarkably nontoxic, was effective when administered in drinking water or by intubation. The ability of the compound to inhibit ornithine decarboxylase in vitro was demonstrated by the reduced amounts of putrescine synthesized from tritiated ornithine in Trypanosoma brucei suspensions. These observations direct attention to polyamine metabolism as a target for chemotherapy of parasitic diseases.

Experimental infections of laboratory rodents with recently isolated stocks of Trypanosoma brucei gambiense. 1. Parasitological investigations

Albino rats and white mice were infected with populations of Trypanosoma brucei gambiense isolated from patients in four different areas in Central Africa. Differences in virulence as shown by the level of parasitaemia, number of relapses, and length of survival time, were observed amongst the stocks according to their geographical origin and secondarily to the degree of adaptation to the rodents. All the stocks are pathogenic for the laboratory rodents, and the presence of extravascular trypanosomes in the brain was confirmed in all infected animals. Spleen, liver, and kidneys were less constantly found to be positive. The morphology of the extravascular parasites was highly variable, ranging from long slender trypomastigotes to spheromastigotes and even amastigotes.