Tropical medicine and parasitology : official organ of Deutsche Tropenmedizinische Gesellschaft and of Deutsche Gesellschaft fur Technische Zusammenarbeit (GTZ)最新文献

In a previous study, three in vitro methods for the assessment of drug sensitivity among Trypanosoma evansi isolates were compared--a direct counting method, pyruvate production method and uptake of radiolabelled hypoxanthine. The pyruvate assay system, which measures the amount of pyruvate in the supernatant of growing populations of trypanosomes by a spectrophotometric method, was selected for further investigation with regard to its suitability for field studies. The effect of initial seeding density and incubation time on the growth of three stocks of T. evansi--TREU 1840 and TREU 1981 (suramin sensitive) and TREU 2136 (suramin resistant)--and drug sensitivities revealed by the pyruvate assay and direct counting were examined to optimise assay conditions. Maximum densities and pyruvate production achieved were not affected by varying the initial seeding densities in the range of 5 x 10(4)-5 x 10(5)/ml and had been reached after 48 hours incubation with one exception: Pyruvate levels continued to increase up to 72 hours in the suramin resistant stock. However, inhibition curves were affected by initial seeding density and incubation period. Results suggested that an initial seeding density of 1 x 10(5)/ml and an incubation time of 48 hours are optimal for the assay. Using these assay conditions, the isolates were screened against suramin, quinapyramine sulphate and Cymelarsan, the trypanocides used most commonly against T. evansi. This assay proved to be a relatively simple and cheap technique applicable to screening large numbers of isolates of differing sensitivities to trypanocidal drugs.

Recommendations state that, where the risk of tuberculosis is high, BCG should be administered to infants as early in life as possible, even if the mother is known to be HIV-infected. BCG should be withheld from individuals with symptomatic HIV infections. However, continuing reports from sub-Saharan Africa and elsewhere of BCG complications in HIV-infected persons call for a re-assessment of current vaccination policies. For HIV-infected infants any benefit of BCG vaccination may be marginal because the prognosis is very poor. It is however not possible to exclude HIV-infected children from BCG vaccination at birth. HIV-uninfected infants born to HIV-infected mothers are at great risk of tuberculosis infection, which justifies routine vaccination. BCG rarely causes serious complications. Theoretically, persons with asymptomatic HIV infection may be at greater risk of complications from BCG vaccines, but available data are inconclusive in that respect. To vaccinate children with BCG at one year of age does not seem feasible and would increase the risk of tuberculosis especially for uninfected infants of HIV seropositive mothers. Available data seem to indicate that routine vaccination of newborns is indeed safe, even in areas with high prevalence of HIV infection.

Ten taxa of Stomoxyinae were tested for their ability to transmit Trypanosoma brucei, T. vivax, T. evansi and T. congolense to mice within 3 min of interrupted feeding on highly parasitaemic blood. T. brucei was the easiest parasite to transmit with an 11.5% success rate, followed by T. vivax at 3.4%, and T. evansi at 0.9%. T. congolense was not transmitted in 129 attempts. Stomoxys niger sspp. and four unstudied species (S. varipes, S. taeniatus, S. pallidus, Haematobosca squalida) were capable of transmitting trypanosomes mechanically.

In the course of epidemiological and immunological baseline studies parasitological surveys were conducted, in 1992, in three localities situated in our near rain forest in the area of Lambaréné, Gabon, western Central Africa. Anopheles gambiae s.s. and A. funestus are considered to be the main vectors of malaria. The three localities represent strata with obvious differences in the intensity of malaria transmission. The lowest parasite rates were recorded in the village around the Albert-Schweitzer-Hospital where environmental sanitation and easy access to diagnostic and therapeutic facilities afford a fair measure of malaria control. The villages of Bellevue and Tchad show a much higher prevalence of Plasmodium falciparum, followed by P. malariae and P. ovale. In all three villages parasite rates and geometric mean parasite densities of P. falciparum showed the age pattern typical for areas with stable, hyperendemic malaria. Analysis by season showed the period of the long rains to be the epidemiologically calmest while the dry season and even more the short rainy season produced an increase of parasite rates and densities. In Tchad, the most affected of the three villages, the parasite rates in female adults were significantly lower than in male adults. This was accompanied by lower parasite densities in female adults.

The resurgence of malaria in form of resistance against chloroquine (CQ) has decreased the importance of the drug as a chemotherapeutic agent. If an agent in combination with CQ can make CQ resistant plasmodia susceptible to CQ, the problem of drug resistance may then be solved. Use of conventional drugs like verapamil, desipramine along with CQ suggested the feasibility of this approach. This report is concerned with a new class of compound, CDRI compound 87/209 (15 mg/kg b. wt.) which is given in combination with chloroquine (10 mg/kg b. wt.) for 10 consecutive days to chloroquine resistant P. berghei/P. yoelii nigeriensis (multidrug resistant) infected Mastomys coucha/Swiss albino mice respectively, displayed a potential in curing the animals. A tentative mode of action of the CDRI compound 87/209 based upon its unique property of inhibiting heme-oxygenase (a heme degrading enzyme) has been presented. It is likely that CDRI compound 87/209 in combination with chloroquine may reverse the resistance acquired by the malarial parasites and in combination with CQ is capable of clearing the parasite from the animals.

Chronic hyperactive dermatitis (sowda) in humans infected with the filarial parasite Onchocerca volvulus appears to reflect a hyperresponsiveness to parasite antigens. To identify antigens which play a role in this hyperresponsiveness an expression cDNA library of adult O. volvulus was screened with sera from patients with sowda. One further characterized cDNA clone, S1, consisting of 723 bp, surprisingly shows open reading frames (ORF) in both orientations. While a single ORF of 171 amino acids is present in sense orientation, a putative ORF of 95 AA is found in antisense orientation (aS1). Whereas no homologies to known proteins are found in S1, the sequence of aS1 shows a striking structural homology to human CC chemokines. The genomic organization of the coding region of aS1 shows the conserved three exon/two intron structure of the CC chemokine family. In adult worms transcription of mRNA corresponding to S1 but not to aS1 was detected. Expression of S1 as a non fusion protein and Western blot analysis revealed antibody recognition by all sera from patients with sowda, by 60% of sera from patients with the generalized form of onchocerciasis, but not by sera of exposed individuals with no evidence of onchocerciasis. IgG subclass analysis showed that IgG3 reactivity was restricted to sowda sera. In adult worms the S1 protein was localized to the hypodermis. Here we present the cloning and characterization of an O. volvulus antigen, which may be useful in the diagnosis of onchocerciasis. Furthermore, the results suggest the presence of a gene structurally related to human inflammatory cytokines in antisense orientation, raising the question of bidirectional transcription in O. volvulus.

The rapid acquisition of resistance by Plasmodium falciparum to antimalarial drugs has focused worldwide efforts on vaccine development. The definition of critical antigens involved in the induction of protective immunity against disease is essential. Our previous studies have characterized a synthetic peptide complex (SPf70), derived from a 70 kDa P. falciparum exoantigen, in terms of its immunogenicity and antigenic reactivity. In the present study total anti-P. falciparum asexual blood-stage antibodies and antibodies to the Pf70 antigen were measured by immunofluorescence (IFA) and ELISA, respectively, in children and adults (n = 160) of Kinshasa, Zaire, an area with continuous and intense malaria transmission. All of the subjects tested had IFA antibodies and 90% (143/160) had antibodies to Pf70 antigen. Antibody levels against Pf70 were significantly higher among children with low parasitemias (p < 0.05). These results suggest that antibodies to Pf70 antigen may have a protective role against P. falciparum infection. Further studies are needed to define the functional nature of the protective mechanism(s).

A survey on intestinal parasites in a rural area of Tanzania revealed the presence of eight protozoa and seven helminths in 287 subjects (81.8%). The prevalence of Entamoeba histolytica and Ascaris lumbricoides was higher in HIV-negative than in HIV-positive patients (P < 0.01; P < 0.04) (25.1% and 12.5% for E. histolytica; 10.5% and 3.7% for A. lumbricoides). On the other hand, Cryptosporidium parvum, Isospora belli and Strongyloides stercoralis prevalence was higher in HIV-positive than in HIV-negative patients (P < 0.01). The prevalence of these two opportunistic protozoa was also higher in AIDS patients than in HIV-positive patients without AIDS. Specific anti-C. parvum IgG were detected by ELISA in 18% and 56% of HIV-negative and positive patients, respectively, confirming the high number of contacts between this parasite and humans. Specific anti-Encephalitozoon cuniculi and anti-Encephalitozoon hellem IgG were detected by IFA in 18% and 19% of subjects, respectively, without any correlation with HIV and malaria infections.

The viability of Acanthamoeba cysts after they have been stored in water at 4 degrees C for a period of 24 years was determined and to estimate their present degree of virulence as compared to its primary values. The viability of 17 amoebae isolates was examined using the eosin exclusion and in vitro excystation on agar plates (NNE). After the period of 24 years, only 3 isolates were found dead. The remaining 14 isolates after inoculation on NNE gave rise to new subcultures, although the percentage of living cysts measured by eosin exclusion was low (0-5%). Separate groups of mice were inoculated intranasally with 10 subcultures characterised by varying primary virulence. It was found that in 8 groups the mice were invaded (at varying degree), and some of them died. Taking into consideration the fact that some of the examined isolates completely lost their virulence only after 8 years of the in vitro cultivation, the obtained results are very intriguing. On the ground of these results one can assume that in the natural environment the period of viability for a cyst may be not shorter than 25 years, and, which is even more essential, they can maintain their invasive properties.

The purpose of this study was to investigate the ability of the antimalarial drug, Ro 42-1611 to block parasite mediated cytokine induction in vitro as well as cytoadherence of infected erythrocytes to melanoma cells in vitro. The biological activity of Ro 42-1611 was confirmed as it blocked Plasmodium falciparum growth in cultures. Ro 42-1611, had no major effect on TNF, IL-alpha or IL-6 cytokine release from mononuclear cells stimulated with malaria antigens or lipopolysaccharide and it did not affect cell viability. Ro 42-1611 only slightly suppressed cytoadherence of infected erythrocytes to melanoma cells. The therapeutic effect of To 42-1611 appears to be confined to its parasite killing activity.