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PubMed1965

PALEOGENESIS AND PALEO-EPIDEMIOLOGY OF PRIMATE MALARIA.

The Haemosporidia, which comprise the malaria parasites, have probably evolved from Coccidia of the intestinal epithelium of the vertebrate host by adaptation first to some tissues of the internal organs and then to life in the circulating cells of the blood.The present opinion is that, among the malaria parasites of primates, the genus Hepatocystis and the "quartan group" of plasmodia are the most ancestral, followed by the "tertian group"; from the evolutionary viewpoint the subgenus Laverania is probably the most recent.Studies recently completed and research in hand on malaria parasites of apes and monkeys, combined with the possibility of assessing the infectivity of new simian parasites to Anopheles and to man, will be of great importance for a better understanding of the probable evolution of primate malarias. The fact that several genera of the Anthropoidea evolved in an ecological area where the association with the existing insect vectors of various plasmodia was close is suggestive of Africa as the original home of primate malaria. It is probable that the disease spread up the Nile valley to the Mediterranean shores and Mesopotamia, to the Indian peninsula and to China. From these main centres malaria invaded a large part of the globe.It is also probable (though not proved) that malaria existed in the Americas before the Spanish conquest, and there is some likelihood that sea-going peoples brought it to the New World long before Columbus's voyages. Modern immunological methods applied to the study of the mummified remains of ancient inhabitants of America may help to solve this question.

Africa↗

PubMed1989

Cell lines from Culicoides variipennis (Diptera: Ceratopogonidae) support replication of bluetongue virus.

Cell lines have been developed from 2-day-old embryos of the biting midge, Culicoides variipennis (Diptera: Ceratopogonidae). In North America C. variipennis is the primary insect vector of bluetongue virus (BTV), an orbivirus that causes disease of ruminants. The C. variipennis (CuVa) cells, grown in Schneider's Drosophila medium, consist primarily of a fibroblast-like cell type. CuVa cells are very hardy. They can grow over a wide range of temperature and pH and adapt to growth in minimal essential medium. BTV replicates to high titer (7.5-8.0 log10 50% tissue culture infectious doses/ml) in CuVa cells over a wide range of temperatures (19 degrees to 37 degrees C) without inducing any significant cytopathic effects. The highest BTV titers were obtained in CuVa cells grown at 25 degrees and 32 degrees C. Cells from C. variipennis can be useful for many diverse investigations.

Animals↗

PubMed1975

The control of bluetongue in an enzootic situation.

On account of the wide host range of bluetongue virus and its biological transmission by insects, control of the disease in an enzootic situation is based primarily on the active immunisation of susceptible animals as well as on the prevention of contact between the insect vectors and the susceptible hosts. In spite of their unquestionable value, the egg attenuated vaccines which are currently employed for prophylactic immunisation, have certain shortcomings. The existence of 16 known serotypes of bluetongue virus makes it difficult to achieve a very wide spectrum of immunity in sheep vaccinated once or twice only. The problems which are experienced with the immunisation of lambs born in spring are indicated. The present vaccine can also present problems when used in breeding animals. Furthermore, the costs involved in the annual vaccination of large numbers of animals are considerable. The need for a vaccine for cattle is indicated. Work is also being conducted at present on the development of an inactivated vaccine for use in sheep. The use of novel virological techniques may aid in the future development of absolutely safe and highly efficient vaccines against bluetongue.

Animals↗

PubMedDate not supplied

Experimental leishmaniasis in humans: review.

Experimental infection of humans with Leishmania parasites has contributed significantly to the understanding of the etiology, transmission, and pathogenesis of leishmaniasis and the immunity associated with it. Leishmania organisms recovered from human and animal tissue, insect vectors, and in vitro cultures have all produced cutaneous or visceral leishmaniasis in human subjects who were voluntarily inoculated with them. Volunteers bitten by infected Phlebotomine sandflies also developed cutaneous or visceral disease. In these experiments, it appeared that the parasite must undergo certain developmental changes within the sandfly for it to become infective and that the parasites in sandflies were far more efficient in causing full-blown infection than were cultured Leishmania organisms. The clinical manifestations of these experimental infections did not differ from infections that were acquired naturally. Natural or experimental infections appeared to confer resistance to subsequent leishmanial infection. This immunity was best documented to be a species-specific phenomenon; however, a small number of studies have demonstrated cross protection between some Leishmania species. In this review article, data from human experimental infections are summarized and discussed in light of recent advances in the field.

Animals↗

PubMed1986

Stage-specific surface antigens of metacyclic trypomastigotes of Trypanosoma cruzi identified by monoclonal antibodies.

Stage-specific Trypanosoma cruzi surface antigens were characterized by using monoclonal antibodies (MAb) which bind specifically to the metacyclic trypomastigotes derived from either the insect vector or acellular cultures. A protein with an apparent molecular weight of 90,000 was detected by the MAb 5E7 on the surface of cultured metacyclics of four strains of T. cruzi: G, CL, Y and Tulahuen. The MAb 1G7, which binds to an epitope of the 90 kDa antigen distinct from that recognized by the MAb 5E7, reacted with metacyclics of the G and Tulahuen strains but not of the Y or CL strain. A polypeptide of approximately 82 kDa, identified by the MAb 3F6, was found in the metacyclics of all four T. cruzi strains. The MAb 3F6 also detected a 75 kDa antigen in the G strain metacyclics. The stage-specific MAb and the polyclonal antibodies from mice protected against acute T. cruzi infection by immunization with killed G metacyclics identified the same set of major surface proteins of G metacyclic trypomastigotes.

Animals↗

PubMed1993

Nested and multiplex polymerase chain reactions for the identification of bluetongue virus infection in the biting midge, Culicoides variipennis.

Two polymerase chain reaction tests for the detection of bluetongue viral (BLU) RNA in the principal North American insect vector, Culicoides variipennis, were developed. The BLU serogroup specific test used the highly expressed non-structural protein 1 gene as the target gene and two amplification steps. First a 1228 base pair product was amplified using an outer primer pair, then a second amplification using a nested or internal primer pair produced a 930 base pair product. This nested PCR test was found to be very sensitive detecting an equivalent to 1 plaque-forming unit of BLU viral RNA extracted from infected biting midges. The serotype specific test used a multiplex PCR approach in which five different primer pairs were used simultaneously. Each pair was based on the variable outer capsid protein VP2 gene of the five US serotypes generating specific product which were easily identified by size difference. The sensitivity of the multiplex PCR was less sensitive than the nested-PCR but sufficient for use with field collected samples. These tests provide valuable tools for epidemiologic studies of BLU disease.

Animals↗

PubMed2005

[Impact on the potential epidemic of dengue fever under warming winter in Hainan province].

OBJECTIVE: Impact of climate warming in winter on the potential epidemics of dengue fever in Hainan was assessed. METHODS: Based on historic data of mean monthly temperature in January from 8 weather observation stations, tendency and amplitude of variation were analyzed. Using 21 degrees C as lowest limit of temperature suitable for dengue fever transmission, impact caused by climate warming on dengue fever epidemic was estimated by means of geography information system (GIS), insect vector and epidemiological features. RESULTS: Temperature in winter in Hainan province had shown an obvious increase. The maximum amplitude of increase appeared in Dongfang which was 1.4 degrees C and the minimum 0.5 degrees C in Shanhudao, but the increase amplitude in the other stations was varied from 0.7 to 1.3 degrees C. By the year of 2050, 21 degrees C contour will have moved 190 km or so northward, nearly spanned 6/7 of distance from south to north in Hainan province and under the condition of daily fraction surviving of Aedes aegypti as P = 0.89, Qionghai city which stands north in Hainan province will probably have become epidemic area of dengue fever all year round. CONCLUSION: Climate warming in winter will probably make half or more of the areas in Hainan province with temperature that permitting transmission of dengue fever by 2050. Monitoring and prevention of dengue fever in winter should be emphasized.

Aedes↗

PubMed2006

Genes and environment in susceptibility to visceral leishmaniasis.

Kala azar (KA) is a lethal disease caused by Leishmania parasites (Leishmania donovani s.l.) that multiply in large numbers in deep organs such as spleen and liver. The host immunological response to these organisms is complex and experimental studies in animals have detected a large number of genetic loci involved in the control of infection and disease. We report here on a study in a human population of Sudan carried out during an outbreak of KA. The following conclusions are presented: (1) environmental factors that could have affected the distribution of the insect vector, influenced progression of KA in the initial phase of the epidemics - but they became less important later at the peak of transmission, probably after infected phlebotomies had spread to all parts of the village -; (2) Leishmania population during the epidemics was heterogeneous, suggesting a possible parasite evolution during the outbreak; (3) the incidence of KA varied markedly among age groups, families and ethnic groups. Susceptibility to KA was shown to depend on a locus on chromosomes 22q12 and on NRAMP1 on chromosome 2q35; the data also suggested a third locus in the region 2q23-q24. Overall, this study indicates complex interactions between host genes and environment in the spreading of KA in that population. It is also suspected that the large parasite diversity observed in the outbreak has contributed to disease spreading across host genetic barriers.

Adolescent↗

PubMed2001

Comparative study of enzymes in testes and ovaries from adult Dipetalogaster maximus (Uhler) and triatoma infestans (Klug) (Hemiptera: Reduviidae). correlation with fine structural organization.

Activities of hexokinase (HK), glucose-6-phosphate dehydrogenase (G6PDH), fructose-6-phosphate kinase (F6PK), glutamate dehydrogenase (GlutDH), aspartate aminotransferase (AAT), malate dehydrogenase (MDH) and glycerol-3-phosphate dehydrogenase (GPDH) were determined in tissue extracts of testes and ovaries of adult Dipetalogaster maximus (Uhler) and Triatoma infestans (Klug) (Hemiptera: Reduviidae), insect vectors of Chagas disease. The fine structure organization of the same organs were studied by electron microscopy. Results allow the following inferences: in testes from both species, most of the glucose would be utilized through the glycolytic pathway. Amino acid catabolism for energy purposes appears to be unimportant. The number of mitochondria and the development of the rough endoplasmic reticulum in cells of the spermatogenic line indicate the occurrence of active oxidative metabolism and protein synthesis; in ovaries, levels of G6PDH indicate the existence of an active pentose pathway which would supply the NADPH required for fat and ecdysteroid synthesis. Amino acid catabolism appears to be relatively more important in ovary than in testis. Fat and glycogen are stored in follicular cells of D. maximus; oocytes of both species contain numerous fat droplets. Abundant mitocondria are present in follicular cells and oocytes. A well developed rough endoplasmic reticulum and free ribosomes are also conspicuous in these cells. The malate/aspartate H-transfer system seemed to be relatively more important than the glycerophosphate shuttle in ovaries as well in testes.

Animals↗

PubMed2001

A novel GFP approach for the analysis of genetic exchange in trypanosomes allowing the in situ detection of mating events.

Trypanosoma brucei undergoes genetic exchange in its insect vector by an unknown mechanism. To visualize the production of hybrids in the fly, a tetracycline (Tet)-inducible expression system was adapted. One parental trypanosome clone was transfected with the gene encoding Green Fluorescent Protein (GFP) under control of the Tet repressor in trans; transfection with these constructs also introduced genes for resistance to hygromycin and phleomycin, respectively. An experimental cross with a second parental clone carrying a gene for geneticin resistance produced fluorescent hybrids with both hygromycin and geneticin resistance. These results are consistent with the meiotic segregation and reassortment of the GFP and repressor genes. Fluorescent hybrids were visible in the salivary glands of the fly, but not the midgut, confirming that genetic exchange occurs among the trypanosome life cycle stages present in (or possibly en route to) the salivary glands. In conclusion, the experimental design has successfully produced fluorescent hybrids which can be observed directly in the salivary glands of the fly, and it has been shown that the recombinant genotypes were most probably the result of meiosis.

Animals↗

PubMed1984

Antigenic variation during the developmental cycle of Trypanosoma brucei.

During the complex life cycle of Trypanosoma brucei, changes in the exposed surface antigens occur in both the mammalian host and the insect vector (Glossina spp.). These antigenic changes are associated with alterations of the variant surface glycoprotein (VSG) composition or with the loss of the VSG. In the bloodstream of the mammalian host, trypanosomes successfully evade destruction by the host's immune response by continuously expressing alternative VSGs, at low frequency, which are not destroyed by host antibodies. When ingested by the tsetse fly, the bloodstream trypanosomes rapidly lose their surface coat and surface membrane antigens are exposed which are normally covered in the bloodstream. In the salivary glands of the tsetse fly, the trypanosomes differentiate to the metacyclic stage, which reacquires a surface coat. The antigenic composition of the metacyclics is heterogeneous. The same metacyclic types are expressed regardless of the bloodstream antigenic type ingested by the tsetse fly. In the mammal the metacyclics differentiate to long-slender bloodstream forms but continue to express the metacyclic VSG for at least three days. The next VSGs expressed in the mammalian host appear to be influenced by the antigenic type ingested by the tsetse. The ingested antigenic type is often expressed in the first parasitemia following expression of the metacyclic antigenic types.

Animals↗

PubMed1997

Histopathological studies of Syrian golden hamsters experimentally infected with Leishmania D. infantum.

In the 1980s, infantile visceral leishmaniasis was documented in Al Agamy (Alexandria). The causative agent is Leishmania d. infantum and the insect vector is Phlebotomus langeroni. In this paper, Syrian golden hamsters were chosen as a model animal for histopathological studies of L. d. infantum. Twenty four male hamsters were experimentally infected with L.d. infantum. Every week, two hamsters were sacrificed and parts from the liver, heart, lung, spleen, small intestine and kidney were paraffin sectioned and stained with haematoxylin and eosin or with Giemsa stain. The leishmanial granuloma was the main histopathological changes and the liver was the main organ affected. Leishmanial granulomas were common in the liver, but few in lung and small intestine. The hepatic granulomas increased in surface areas and in number in the late stage of the infection (< 6 weeks). They were formed mainly of histiocytes, less lymphocytes and very few eosinophils with necrosis inside and bridging in between granulomas mainly occurred in the late stage of infection. Neither fibrosis nor peripheral delimitation was seen. Kupffer cell hyperplasia was seen throughout the experimental period (12 weeks). The spleen showed expansion of the red pulp and atrophy of the white pulp. The kidney showed mesangial cell proliferation and the mesangial matrix increased accompanied with amyloid deposition. All the tissue sections were photographed and the results were discussed.

Animals↗

PubMed1996

The developmental expression of Leishmania donovani A2 amastigote-specific genes is post-transcriptionally mediated and involves elements located in the 3'-untranslated region.

Leishmania donovani is a protozoan parasite that exists as a free-living promastigote in the sandfly insect vector and as an amastigote inside the mammalian host macrophage phagolysosome compartment. The L. donovani A2 genes have been described previously as developmentally expressed in amastigotes but can be induced experimentally in promastigotes by a combination of pH and temperature shifts, conditions that mimic the phagolysosomal compartment of the macrophage cell. Considering the importance of the amastigote stage in human infections, we have examined the molecular basis for amastigote stage-specific gene expression. Our results provide evidence that A2 developmental expression during the promastigote-to-amastigote cytodifferentiation is mediated through differential RNA stability and involves the A2 mRNA 3'-untranslated region. The site of processing in the 3'-untranslated region was a major factor for the accumulation of A2 mRNAs in cells incubated under phagolysosomal conditions. The stability of reporter gene transcripts bearing the A2 3'-untranslated region was increased in cells incubated at low pH, further confirming the importance of pH shift as an inducer for A2 expression. These observations contribute to defining the mechanism of amastigote-specific gene regulation in L. donovani. We also demonstrate the feasibility of using the A2 locus to express heterologous genes differentially in the amastigote form of the L. donovani parasite.

Animals↗

PubMed2003

Distribution of sandflies (Diptera: Phlebotominae) in forest remnants and adjacent matrix habitats in Brazilian Amazonia.

We studied the distribution of sandflies (Diptera: Phlebotominae)--insect vectors of several diseases, including leishmaniasis--at the interface between primary forest and cattle pasture and between primary forest and secondary forest (< 15 yr old) in Southern Brazilian Amazonia. Sandflies were collected by using a combination of light traps and traps having vertebrates as baits. Strong differences in abundance and species richness were found between primary forests and pastures. Very few sandfly species were found in the pastures, and those that were found generally occurred at lower densities when compared to the adjacent forest. At least one species (Lutzomyia lainsoni), however, can become extremely abundant in pastures, possibly depending on the presence of cattle and water bodies. Differences between primary forests and secondary forests were not so strong, although the latter usually had fewer species and lower population abundances. No species were exclusively found in pastures or secondary forests; the species present in these two habitats were a subset of those found in primary forests. The distance to the edge did not affect the abundance, richness and composition of sandfly species in primary forests. The abundance and richness of sandflies, however, was greater in forest edges facing pastures than those facing secondary forests. This pattern could not be explained by an influx of species and individuals from the adjacent pasture, suggesting the existence of in situ differences between the different types of forest edges studied.

Animals↗

PubMed2006

Glossina proteolytic lectin does not require a carbohydrate moiety for enzymatic or trypanosome-transforming activities.

The developmental cycle of the cyclically transmitted African trypanosome involves an obligatory passage through the tsetse fly, Glossina spp. This intricate relationship requires the presence of molecules within the insect vector, including a midgut lectin, that interact with the trypanosome. Recently, a gene encoding for a proteolytic lectin, with trypanosome-transforming activity, was isolated from a midgut cDNA library of Glossina fuscipes fuscipes Austen in our laboratory. Using the same approach, we have identified a similar gene from a midgut cDNA library of Glossina austeni (Newstead). The protein encoded by this gene was expressed in bacteria and a baculovirus-based expression system. The baculovirus-expressed lectin was found in the medium of baculovirus-infected Sf-21 cell cultures, indicating that the tsetse fly-derived signal peptide was recognized and cleaved by the Sf-21 cells. The baculovirus-expressed protein also was glycosylated despite the absence of classical O-linked and N-linked sugar attachment motifs. Both the baculovirus- and bacterium-expressed lectin proteins were shown to agglutinate trypanosomes and rabbit red blood cells in vitro. This agglutination was strongly inhibited by D-glucosamine. D-Glucosamine also inhibited the action of the authentic and recombinant lectins upon the chromogenic substrate Chromozym TRY. Interestingly, both baculovirus- and bacterium-expressed lectins showed no significant differences in terms of these activities, indicating that a sugar moiety is not essential for biological activity. Our results provide an important molecular tool for further characterization of Glossina proteolytic lectin.

Amino Acid Sequence↗

PubMed1999

A preliminary attempt to use climate data and satellite imagery to model the abundance and distribution of Culicoides imicola (Diptera: Ceratopogonidae) in southern Africa.

Abundances of Culicoides imicola, the insect vector of several livestock viruses, including bluetongue and African horse sickness, were recently published for 34 sites in southern Africa, together with associated climate data. Here, these data are analysed statistically in combination with certain satellite-derived variables, with the aim of developing predictive models of C. imicola abundance. Satellite-derived variables were the land surface temperature (LST, a measure of temperature at the earth's surface) and the normalised difference vegetation index (NDVI, a measure of photosynthetic activity). Two models were developed: (1) climatic variables only and (2) satellite-derived and climatic variables. For model I, the best model used a single predictor variable (the mean daily minimum temperature) only, and accounted for nearly 34% of the variance in C. imicola abundance. Two variable climatic models did not perform significantly better. For model II, the best 1-variable model used the annual minimum LST as a predictor of C. imicola abundance, and accounted for nearly 40% of the variance in C. imicola abundance. The best 2-variable model, which gave a significantly better fit than the 1-variable model, combined the minimum LST and minimum NDVI as predictors of C. imicola abundance, and accounted for nearly 67% of variance. A map of predicted C. imicola abundances is produced on the basis of this 2nd model which, despite some anomalies, agrees largely with what is currently known of the prevalence of C. imicola in the region.

Africa, Southern↗

PubMed2002

An antibody to the putative aphid recognition site on cucumber mosaic virus recognizes pentons but not hexons.

Cucumber mosaic virus (CMV), the type member of the genus Cucumovirus (family Bromoviridae), is transmitted by aphids in a nonpersistent manner. Mutagenesis experiments identified the betaH-betaI loop of the capsid subunit as a potential key motif responsible for interactions with the insect vector. To further examine the functional characteristics of this motif, we generated monoclonal antibodies that bound to native virions but not to betaH-betaI mutants. Fab fragments from these antibodies were complexed with wild-type CMV and the virus-Fab structure was determined to 12-A resolution by using electron cryomicroscopy and image reconstruction techniques. The electron density attributed to the bound antibody has a turret-like appearance and protrudes from each of the 12 fivefold axes of the icosahedral virus. Thus, the antibody binds only to the pentameric clusters (pentons) of A subunits of the T=3 quasisymmetric virus and does not appear to bind to any of the B and C subunits that occur as hexameric clusters (hexons) at the threefold (quasi-sixfold) axes. Modeling and electron density comparisons were used to analyze the paratope-epitope interface and demonstrated that the antibody binds to three betaH-betaI loops in three adjacent A subunits in each penton. This antibody can discriminate between A and B/C subunits even though the betaH-betaI loop adopts the same structure in all 180 capsid subunits and is therefore recognizing differences in subunit arrangements. Antibodies with such character have potential use as probes of viral assembly. Our results may provide an additional rationale for designing synthetic vaccines by using symmetrical viral particles.

Animals↗

PubMed1983

A note on estimating selection pressures on insecticide-resistance genes.

It is useful to be able to measure selection pressures acting on resistance genes in insect vectors of disease, since it is thus possible to predict future changes in frequency and to consider ways to minimize development of resistance. This note describes a method for estimating the selection coefficients, given two or more post-selection phenotype frequencies and knowing the number of generations between them.The method is applied to published data on Anopheles labranchiae under selection with DDT. The relative fitness (1-s) of the susceptibles compared with resistants was estimated by this method to be 31-38%. This was an annual estimate, but if the number of generations per year is known, it is also possible to calculate a value per generation. A computer program for making these estimates is given. The calculations depend on the gene being effectively recessive, i.e., on the heterozygote being killed by the dose applied in the field.Another approach to estimation of selection is by determining the deviation in gene frequency from the Hardy-Weinberg expectations. By this method, the relative fitness (1-s) of the susceptibles in a population of A. funestris under dieldrin selection in the north of the United Republic of Cameroon has been estimated to be 40%. There are difficulties with this method, however, because population mixing may result in deviations that mimic the effect of selection. Examples are discussed for A. gambiae, where population mixing may occur and heterozygote deficiencies for the dieldrin resistance gene have been observed.For both methods of estimation, it is essential to know the real effective dominance of the resistance gene in the wild, i.e., whether the resistance heterozygote is killed or not. This factor is important in the control of resistance.

Animals↗