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PubMed2003

Insect immunity and its implication in mosquito-malaria interactions.

Insects' resistance to infectious agents is essential for their own survival and also for the health of the plant, animal and human populations with which they closely interact. Several of the major human diseases are spread by insects and are rapidly expanding as a result of the development of insecticide resistance in vectors and drug resistance in parasites. A vector insects' permissiveness to a pathogen, and hence the spread of the disease, will largely depend on the compatibility of the molecular interactions between the two species and the capability of the insect immune system to recognize and kill the pathogen. The innate immune system comprises a variety of components and mechanisms that can discriminate between different microorganisms and mount specific responses to control pathogenic infections. An impressive body of knowledge on the insects' innate immunity has been generated from studies in the model organism Drosophila. These studies are now guiding the exploration of the immune system in the vector mosquito of human malaria, Anopheles, and its implication in the elimination of parasites. Anopheles immune responses have been linked to parasite losses and some refractory mosquitoes can kill all parasites through specific defence mechanisms. The recently sequenced Drosophila and Anopheles genomes provide a detailed and comparative view on their immune gene repertoires that in combination with post-genomic analyses is used to further dissect the complex mechanisms of Plasmodium killing in the mosquito.

Animals↗
PubMed1999

The Southern Cone Initiative against Chagas disease.

Chagas disease (also known as American trypanosomiasis) is now ranked as the most serious parasitic disease of the Americas, with an economic impact far outranking the combined effects of other parasitic diseases such as malaria, schistosomiasis and leishmaniasis. Although the chronic infection remains virtually incurable, transmission can be halted by eliminating the domestic insect vectors and screening blood donors to avoid transfusional transmission. In line with this strategy, governments of the six Southern Cone countries (Argentina, Bolivia, Brazil, Chile, Paraguay and Uruguay) launched in 1991 an ambitious initiative to control Chagas disease through elimination of the main vector, Triatoma infestans, and large-scale screening of blood donors. Now at its mid-point, the programme has achieved remarkable success, with transmission halted over vast areas of the previously endemic regions. Well over 2 million rural houses have been sprayed to eliminate T. infestans, and the programme has already shown significant economic rates of return in addition to the medical and social benefits.

Animals↗
PubMed2005

Expression of a viral polymerase-bound host factor turns human cell lines permissive to a plant- and insect-infecting virus.

Tospoviruses are the only plant-infecting members of the Bunyaviridae family of ambisense ssRNA viruses. Tomato spotted wilt tospovirus (TSWV), the type-member, also causes mild infection on its main insect vector, Frankliniella occidentalis. Herein, we identified an F. occidentalis putative transcription factor (FoTF) that binds to the TSWV RNA-dependent RNA polymerase and to viral RNA. Using in vitro RNA synthesis assays, we show that addition of purified FoTF improves viral replication, but not transcription. Expression of FoTF deletion mutants, unable to bind the RNA-dependent RNA polymerase or viral RNA, blocks TSWV replication in F. occidentalis cells. Finally, expression of FoTF wild-type turns human cell lines permissive to TSWV replication. These data indicate that FoTF is a host factor required for TSWV replication in vitro and in vivo, provide an experimental system that could be used to compare molecular defense mechanisms in plant, insect, and human cells against the same pathogen (TSWV), and could lead to a better understanding of evolutionary processes of ambisense RNA viruses.

Animals↗
PubMed2003

Multilocus enzyme electrophoresis analysis of Trypanosoma cruzi isolates from a geographically restricted endemic area for Chagas' disease in Argentina.

A set of 65 Trypanosoma cruzi stocks from dogs, opossums, insect vectors and humans was isolated in a geographically restricted endemic area for Chagas' disease in Argentina and was analysed by multilocus enzyme electrophoresis for 15 loci. The results show that at least five multilocus genotypes (clonets) circulate in the study area, one belonging to T. cruzi IIe, one to T. cruzi IId and three clonets belonging to T. cruzi I; and they confirm the presence of these lineages in the country. The three clonets attributed to T. cruzi I were identical to each other for all loci except for Sod-2, where three different patterns were identified. These patterns suggest the presence of two homozygous genotypes and one heterozygous genotype. Our results also suggest association of clonet IIe with dogs, clonet IId with humans and the three T. cruzi I clonets with Didelphis albiventris. On the other hand, there was no significant association between Triatoma infestans and any particular clonet circulating in the area. These findings are consistent with the hypothesis of natural selection, from mixed populations of T. cruzi in vectors, toward more restricted populations in mammals. The epidemiological implications of the possible selection of different clonets by different mammal hosts and the significance of two homozygous genotypes and one heterozygous genotype for the Sod-2 locus are discussed.

Animals↗
PubMed2005

Galectins as immunoregulators during infectious processes: from microbial invasion to the resolution of the disease.

Recent evidence has implicated galectins, a family of evolutionarily conserved carbohydrate-binding proteins, as regulators of immune cell homeostasis and host-pathogen interactions. Galectins operate at different levels of innate and adaptive immune responses, by modulating cell survival and cell activation or by influencing the Th1/Th2 cytokine balance. Furthermore, galectins may contribute to host-pathogen recognition and may serve as receptors for specific interactions of pathogens with their insect vectors. Here we will explore the influence of galectins in immunological processes relevant to microbial infection and will summarize exciting recent work related to the specific interactions between galectins and their glycoconjugate ligands as critical determinants of pathogen recognition. Understanding the role of galectin-sugar interactions during the course of microbial infections might contribute to defining novel targets for disease prevention and immune intervention.

Animals↗
PubMed1998

More crops, more disease?

The intensity of disease transmission by insect vectors may be influenced by developments in agriculture and forestry. The author illustrates what can happen with special reference to projects in Thailand and Ethiopia which increased the incidence of malaria, and to the introduction of a new variety of coffee in Colombia, as a result of which the incidence of leishmaniasis among plantation workers decreased. Development programmes need to take predictable disease outcomes fully into account.

Agriculture↗
PubMed1993

Counter immunoelectrophoresis, a modified technique for the identification of blood meals of sandflies collected from Qualyobia Governorate, Egypt.

Specificity and sensitivity are very important when investigating the blood meals of an insect vector, particularly those having different hosts. Several techniques are used for the identification of the blood meals. Counter immunoelectrophoresis is the technique of choice. The modification was to secure save of time and least amount of materials. In this paper, a modified technique of the counter immunoelectrophoresis (CIEP) was used for the identification of the blood meal of wild Phlebotomus papatasi collected from different sites in Qualyobia Governorate. Eight antisera were used. These were human, cat, dog, rat, sheep, goat, bovine and avian. The results showed that 99.52% of 832 female P. papatasi contained human blood, 0.12% (one female) contained only avian blood and 0.36% or three females each contained mixed blood of human together with dog blood (One), rat blood (one) or avian blood (one). P. papatasi is an anthropophilic insect, but in rare cases, it is zoophilic.

Animals↗
PubMed2001

An ecosystem approach to human health and the prevention of cutaneous leishmaniasis in Tumaco, Colombia.

A study was conducted during 1996-1997 in 20 villages of Tumaco, Colombia, to evaluate the effectiveness of personal protective measures against cutaneous leishmaniasis (CL). The intervention was effective, but the high costs of the preventive measures and the lack of a more holistic approach hampered the intervention's sustainability. This paper analyzes the results using an ecosystem approach to human health. Using this approach, we found that CL has been present in the study area for a long time and affects farmers and those living closest to the forest. The forest constitutes the habitat for insect vectors (sandflies) and parasite reservoirs (wild mammals). Four spatial scales were identified in this ecosystem: residential, village, regional, and global. From the ecosystem perspective, three interventions are proposed to prevent CL in the 20 villages: improve housing construction, organize village housing in clusters, and make diagnosis and treatment of CL more accessible. The design and implementation of these interventions require active involvement by people with the disease (village inhabitants) and decision-makers (local authorities).

Animals↗
PubMed2004

Delivery of a genetically marked Alcaligenes sp. to the glassy-winged sharpshooter for use in a paratransgenic control strategy.

An artificial feeding system was designed for the glassy-winged sharpshooter (GWSS), Homalodisca coagulata Say (Hemiptera: Cicadellidae). The system, unlike previous systems, provided enough nutrients to GWSS to survive for 48 h. A system like this is a prerequisite to examining the potential use of paratransgenesis to interrupt transmission of Xylella fastidiosa, the bacterial pathogen causing Pierce's disease of grape, by insect vectors. We developed a system for short-term feeding of GWSS that allows for the introduction of bacteria in liquid medium, and we have demonstrated the ability of Alcaligenes xylosoxidans denitrificans, expressing a red fluorescent protein (dsRed), to colonize the cibarial region of the GWSS foregut for up to 5 weeks post-exposure. Alcaligenes xylosoxidans denitrificans thus occupies the same region in the foregut as the pathogen, Xylella fastidiosa.

Alcaligenes↗
PubMed1993

Prevalence of Chagas' disease in Ayoreo communities of the Paraguayan Chaco.

The prevalence of Chagas' disease in Ayoreo amerindians living in their traditional habitat of the Paraguayan Chaco was assessed by ELISA and indirect immunofluorescence techniques. The Ayoreo is the last hunther-gatherer tribe of the Paraguayan Chaco and was "pacified" between 1965 and 1975. They still maintain a seminomadic way of life. Chagas' disease prevalence in the Ayoreo communities probably represents their natural prevalence in Chaco Amerindians before settlement. Triatoma sordida was identified as the insect vector in the settlements of Gesudi and Chovoreca, while the highly domiciliary Triatoma infestans was found in Campo Loro. The prevalence of Chagas' disease in Gesudi and Chovoreca, based on our serological surveys was 12-13%. Other authors reported a 72.9% of Chagas' disease prevalence in amerindians settled in the Chaco since 1930-1940.

Adolescent↗
PubMed1998

[Canine leishmaniasis. New concepts of epidemiology and immunopathology: their impact in the control of human visceral leishmaniasis].

Visceral leishmaniasis (VL) is a zoonosis in most regions where it occurs. Dogs are the most important reservoir of the disease and are mainly responsible for the persistence of VL in the Paleartic and Neotropical regions. Canine leishmaniasis (CaL) is a viscerocutaneous, chronic infection with a worse prognosis than human disease. We now know that, as in man, there are some cases of asymptomatic infection. Former studies indicated that dog cutaneous parasitism becomes infectious to the insect vector in later periods of the disease, but recent studies performed by xenodiagnosis have shown that it is possible that transmission might occur earlier. The infected animal reacts with a great production of antibodies and depression of cellular immunity. Antibodies are not protective and resistance is related with active cellular immunity. The presence of Th 1 response in asymptomatic animals, sometimes without humoral response, means that the prevalence of CaL, found in epidemiological surveys by searching for antibodies, may be underestimated.

Animals↗
PubMed2003

[Human activities and American trypanosomiasis. Review of the literature].

Trypanosoma cruzi, the causative agent of American trypanosomiasis (Chagas disease) is a parasite of wild mammals of Americas. It has been further transmitted to man through an insect vector belonging to the Reduviidae family. In the context of an ecoepidemiological study of this vector borne anthropozoonosis, a medical anthropological overview tries, by using data from literature, to clarify the different ways human activities play on the disease epidemiological cycle. The everyday human activities support domiciliation of triatomine bugs. But, the human intervention in the natural environment disturbs strongly the ecology of the vectors or hosts and leads to a new structuring of the natural foci of the disease with its displacement toward the human environment. The way society or individuals manage the disease plays also an important role. Some human activities, as building dwelling structures, have been well studied, but some others, such as the real impact of the human modes of production, are less known. A medical anthropology study of the role of human activities on the foci of Chagas disease is still needed.

Agriculture↗
PubMed1965

THE SALIVARY GLAND CHROMOSOMES OF ANOPHELES OCCIDENTALIS.

Increasing emphasis is being placed on the study of the genetics of insect vectors of disease, and, although Anopheles occidentalis is not itself a malaria vector, study of its salivary gland chromosomes is important as part of investigations into the phylogenetic and evolutionary relationships of anophelines, especially in view of this species' close morphological similarity to other members of the A. maculipennis complex.The authors of this paper provide a map of the salivary chromosomes of A. occidentalis, and discuss the many points of resemblance of those chromosomes to those of A. freeborni in particular. However, they point out that at least ten different paracentric inversions must be postulated to derive the A. occidentalis chromosomes from those of A. freeborni.

Animals↗
PubMed1975

The epizootiology of bluetongue: the African situation.

Bluetongue virus is transmitted biologically by various species of Culicoides, notably C. pallidipennis and C. variipennis. Factors such as rainfall, temperature and relative altitude, which influence the breeding of the insect vectors also govern the incidence and distribution of the disease. The host range of bluetongue virus includes sheep, cattle, goats and various antelopes. Many other, as yet unidentified hosts could perhaps harbour the virus and influence the epizootiology of the disease. The close relationship between C. pallidipennis and cattle is indicated and the efficient mechanism for virus maintenance which this relationship constitutes is emphasised. It is further postulated that sheep are not essential for the continued survival of bluetongue virus, but merely function as accidental or indicator hosts.

Africa, Southern↗
PubMed1994

Phylogenetic characterisation of bluetongue viruses from naturally-infected insects, cattle and sheep in Australia.

The polymerase chain reaction was used to detect the presence of bluetongue virus (BTV) in a number of clinical and insect samples collected in the Northern Territory of Australia. Sequence analyses of the amplified BTV genes differentiated endemic Australian and exotic viruses. Two potential exotic BTV were detected as a result of PCR analyses of blood from sentinel animals and of the insect vector, Culicoides wadai. The detection of BTV in C wadai was the first direct demonstration of the presence of BTV in this potential vector. This new technology can significantly reduce the time taken for a diagnosis from a clinical sample and increase the amount of useful information obtained on a BTV isolate by using rapid sequencing techniques. Sequence data were used to differentiate between BTV20 isolated in 1975 and two isolates of the same serotype, isolated in 1992, and indicated that the latter were probably a recent incursion into Australia from Indonesia due to their greater VP3 sequence homology to the BTV9 (Java) than to Australian BTV isolates.

Animals↗
PubMed1981

Non-Mendelian inheritance of mosquito susceptibility to infection with Brugia malayi and Brugia pahangi.

The mode of inheritance of susceptibility or refractoriness of insect vectors to medically important pathogens such as those causing malaria or filariasis is usually believed to follow normal Mendelian laws and to involve a single pair of alleles. In this report, experiments are described that demonstrate another mode of inheritance of mosquito susceptibility to filarial parasites. Crosses were made between susceptibile and refractory species of the Aedes Scutellaris complex, and the hybrid and backcross progeny were tested for susceptibility to infection by Brugia malayi and Brugia pahangi. The data indicate that inheritance follows a non-Mendelian pattern indicative of extrachromosomal factors inherited through the maternal parent.

Aedes↗
PubMed1985

The search for bluetongue viruses in Australia.

In the 200 years that cattle and sheep have been present in Australia no evidence of bluetongue (BT) disease has ever been reported. The discovery in 1977 that a virus isolated from Culicoides species collected in 1975 was bluetongue virus (BTV) triggered a search for BT viruses and their vectors throughout the country. Between 1975 and 1983, 46 strains of 5 serotypes of BTV were isolated by various workers from the blood of subclinically infected sentinel cattle or from Culicoides species. The serotypes are 1, 20, 21 and 2 others not yet fully characterized. By testing stored sera from cattle and buffaloes, antibodies to serotype 21 were found in sera collected in 1958, but antibodies to serotypes 20 and 1 were not found earlier than 1973 and 1969 respectively. Discrepancies between the results of BTV group antibody and neutralizing antibody surveys indicate that other serotypes may yet be found. Neutralizing antibodies to BTV have been found in cattle, buffaloes, deer, goats and sheep, but mammals indigenous to Australia are apparently not being infected. In the course of the search, Ibaraki virus and 4 other viruses of the epizootic haemorrhagic disease (EHD) group were found. Infection with EHD viruses has produced heterotypic antibodies detected in tests for BT group antibodies. The prevalence of antibodies to BT and EHD viruses in cattle is greater in the northern 1/3 of the continent than the middle 1/3 while the southernmost 1/3 is free. By the sequential sampling of sentinel cattle it has been determined that infection with BT and EHD viruses occurs mainly in the latter part of summer, and autumn. The seasons of the year, and the locations from which BT and EHD viruses originated were consistent with the serological findings. Isolations of BT and EHD viruses have also been made from insect vectors, BTV serotype 1 from C. fulvus and C. brevitarsis, plus serotype 20 from a mixed pool of Culicoides species and 2 different EHD viruses from C. brevitarsis. The susceptibility of other Culicoides species to experimental infection with BT and EHD viruses suggests that they may be involved in the natural spread of these viruses. BT and EHD viruses appear to be non-pathogenic for cattle under experimental conditions, but mildly or moderately pathogenic for sheep. The clinical signs produced are consistent with those produced experimentally in other countries.

Animals↗
PubMed1998

Compared vectorial transmissibility of pure and mixed clonal genotypes of Trypanosoma cruzi in Triatoma infestans.

A total of 15 mixtures involving 9 different stocks attributed to the 19/20, 32 and 39 major clonal genotypes of Trypanosoma cruzi were used to infect third-instar nymphs of Triatoma infestans via an artificial feeding device. Three biological parameters were considered: (1) the percentage of infected insects (%II), (2) the number of flagellates per insect (NFI), and (3) the percentage of trypomastigotes per insect (%DIF). Genetic characterization by both multilocus enzyme electrophoresis (MLEE) and random amplification of polymorphic DNA (RAPD) indicated that in almost all cases (87%), mixtures remained present after completion of the whole cycle in the insect vector. Two lines of comparison were performed: (1) pure clonal genotypes versus corresponding mixed clonal genotypes and (2) the actual behavior of mixed clonal genotypes versus the expected behavior of the theoretical mixture (i.e. the arithmetic mean of the results observed for each of the two clonal genotypes taken separately). Statistical analyses of the variables were made difficult because of the presence of large standard deviations. Nevertheless, in several cases, mixtures differed significantly from pure clonal genotypes, and in one case the actual mixture differed significantly from the theoretical mixture. In some cases, interaction (either potentialization or reciprocal inhibition) could be suspected.

Animals↗