Tropenmedizin und Parasitologie最新文献

The cuticle, hypodermis and musculature of first, second and third stage larvae of Wuchereria bancrofti from the mosquito vector were studied by transmission electron microscopy. The young first stage larva is characterized by a thick cuticle with distinct layers demonstrating oriented fibrils. The muscle cells are well developed while the hypodermis has undifferentiated cytoplasm. - The late first stage larva (sausage-stage) still has a thick cuticle but the fibrils are no longer discernible. The volume of the hypodermal cells increases considerably, their plasma shows an abundance of organelles. The muscle sectors are shifted apart from each other by the growth of the hypodermis. The muscle cells are small, they start to multiply. - The cuticle of the second stage larva consists of three thin laminae only. The number of the hypodermal cells increases. They form the characteristic hypodermal chords. The four muscle sectors contain poorly developed muscle cells which multiply until the onset of the second moult. - The third stage larva shows a thick, multilayered cuticle with fibrous sublayers. Hypodermis and musculature are well differentiated. The hypodermal chords protrude into the centre of the worm. The muscle cells have grown considerably and their outer fibrillar portions show beginning septation.

Microfilarial skin snip counts from savannah and rain forest areas of West Africa and from Central America were analyzed. Before parametric statistical tests, such as the comparison of means, can be properly performed, the variance must be independent of the mean. The best transformation of the skin snip counts to make the variance independent of the mean was determined. Frequency distributions of skin snip counts are shown for several different transformations. In three out of four sets of data that were examined, the best transformation was found to be the fourth root of the counts, not the logarithm of the count as has been customarily used.

Simulium sanctipauli and S. yahense have been incriminated as the main vectors of Onchocerca volvulus in the rain-forest zone of Liberia. An accurate identification of the females of the two species which breed in different types of water-courses but are morphologically similar is essential for a proper study of their epidemiological importance and the planning of control measures. Various external characters were examined for their diagnostic value by the comparison of identifications using these characters and those based on enzyme electrophoresis (phosphoglucomutase, trehalase). It was shown that the females of the two species can be separated reliably by the use of external morphological characters. The occasional finding in the same fly of phosphoglucomutase variants typical for each species indicated the possible occurrence of natural hybridization between S. sanctipauli and S. yahense.

In order to study the occurrence and sequential appearance of antigenic variation during the course of T. evansi-infection, rabbits were infected with a clone prepared from T. evansi, Java/55/PTV/1 (stock 1, clone 5). During the course of infection, trypanosome-populations were isolated from the cerebrospinal fluid and from each parasitaemia peak. Specific antisera against the clone, 6 parasitaemia-populations and two different liquor-populations (all isolated from 1 rabbit), were produced in rabbits. These antisera were used for the characterization and comparison of trypanosome populations with each other by means of immunolysis as well as neutralisation-infectivity-(NIF)-test. It was found that in all infected rabbits, the first parasitaemia contained trypanosomes, which were almost identical to those present in the clone. However, the clone contained already minor variant antigenic types ("minor-VATs"). All trypanosome-populations isolated from rabbits were heterogeneous. Heterogeneity was more pronounced in the later phases of the infection. After each fluctuating parasitaemia new dominant variants ("major VAT") were expressed. The sequential appearance of antigenic variation was similar among all infected animals. The effectivity of immunolysis was checked by the NIF-test. As it was expected, complete lysis of all trypanosomes of a population was not achieved, because some "minor VATs" could escape the influence of the antiserum. By this way, they formed the basis of new "major VATs" which dominated in the next fluctuating parasitaemia.

Simulium ornatum s.l. is a natural vector of Onchocerca lienalis in Britain. These studies investigated the role of the blood meal on the development of the parasite in the thoracic musculature. Infection was by the standard technique of intrathoracic injection, allowing precise doses of microfilariae to be administered. Prior to infection flies were fed on bovine blood through a chick skin membrane. In 3 trials the number of O. lienalis larvae developing in non-blood fed flies was between 60.2 and 68.4% lower than in blood fed insects. The mean number of eggs recovered per fly ranged from 131.7 to 187.5 in infected groups. In uninfected control groups the levels ranged from 315.4 to 378.1 per fly. This represents reductions in fecundity of between 50.4 and 51.7% in infected groups of simuliids. It appears that in order to maintain relatively high levels of transmission an intermediate blood meal, between uptake of microfilariae and release of infective stage larvae, may be important. Furthermore, great care must be taken when using fecundity to assess the age of simuliids. Levels of parasitic infection may affect egg production to a much greater extent.

A survey based on microscopic examination of scrapping taken from the gum-line was conducted on the prevalence of Entamoeba gingivalis amongst inhabitants of the Niger Delta area of Nigeria. An overall prevalence of 6.9% was recorded. Infection was highest among the 5-10 year age group (22.9%) and dropped progressively with increase in age of the subjects such that by the age of 29 years it had fallen to 5.7%. No significant difference (p less than 0.005) could be detected regarding infection amongst smokers (4.1%) and non-smokers (4.3%) or between male (6.8%) and female subjects (7.0%).

Tsetse, caught in biconical traps near Bouaflé, Ivory Coast in 1980-81, were examined for trypanosome infections. In a sample of 1138 non teneral Glossina palpalis s.l. there were infection rates of 12.2% (all infections) and 5.3% (mature infections). Female flies had a significantly higher infection rate than males. In G. palpalis only 3 (0.26%) salivary gland infections were detected, 62.3% of the mature infections were T. vivax-like and 71.4% of all infections were restricted to the midgut. The infection rate in forest/plantation caught G. palpalis was twice that of village caught flies. The infection rate increased with fly age and is correlated in female flies. In smaller samples of G.p. pallicera and G. fusca group flies the trypanosome infection rates were 37% and 46% respectively. In both these groups of flies 64.7% of infections were mature and were predominantly T. vivax-like and in females.

The model of Onchocerca lienalis microfilariae injected into inbred CBA/HT6T6 mice has been examined for its value to study immunity to the skin-dwelling microfilariae in onchocerciasis. Mice injected with living microfilariae during primary or secondary infections exhibited a high level of resistance to challenge relative to normal controls (91-98% reduction in recoveries). The survival of microfilariae during a primary infection was significantly prolonged in T-cell deprived animals compared with immunologically intact mice. Serum and spleen cells transferred from donors 90 days after infection conferred significant protection in syngeneic recipients to challenge with microfilariae (59% reduction in recoveries compared with controls). Boostered injections with freeze-killed or fragmented microfilariae reduced parasite recoveries after challenge by 39-78%: none of 5 adjuvant preparations enhanced the protective effect. Mice exposed to living infective larvae or adult males of O. lienalis also exhibited lowered recoveries of microfilariae following a challenge infection. It is concluded that the mouse model offers potential for immunological studies on the microfilariae in onchocerciasis, which have hitherto been limited because of the lack of suitable laboratory hosts.

The ELISA test titers and RIPA patterns of sera collected from vaccinated and non-vaccinated rats during P. berghei infection were similar. The sera collected just after clearance of parasitemia from the vaccinated rats, but not that from the non-vaccinated rats protected mice in passive protection tests. After precipitation to remove immune complexes, the sera from the non-vaccinated rats also protected mice. Administration of acute phase serum early in the course of infection aggravated parasitemia and delayed recovery from P. berghei infection in rats. Administration of hyperimmune serum early in the course of infection initially reduced parasitemia but then delayed recovery of rats from P. berghei infection. These results suggest that immune complexes may interfere with antibody mediated immunity to P. berghei and may also retard development of the induced immune response.

A cloned stock of T. evansi was shown to undergo antigenic variation giving rise to 11 antigenic variants during the first 30 days of infection in rabbits. Ten of the 11 variable antigen type (VAT) populations isolated during this study were shown to represent predominant VATs of the stock as each of these 10 VATs was shown to develop early in infection in rabbits infected with different VATs of the stock. The probability, therefore, exists that stocks of T. evansi can be classified into VAT-serodemes on the basis of their predominant VAT repertoires for use in epidemiological studies.