Competency of Anopheles stephensi mysorensis strain for Plasmodium vivax and the role of inhibitory carbohydrates to block its sporogonic cycle

<p>Abstract</p> <p>Background</p> <p>Despite the abundance of studies conducted on the role of mosquitoes in malaria transmission, the biology and interaction of <it>Plasmodium </it>with its insect host still holds many mysteries. This paper provides the first study to follow the sporogonic cycle of <it>Plasmodium vivax </it>in a wild insecticide-resistant mysorensis strain of <it>Anopheles stephensi</it>, a major vector of vivax malaria in south-eastern Iran. The study subsequently demonstrates that host-parasite sugar binding interactions are critical to the development of this parasite in the salivary glands of its mosquito host. The identity of the receptors or sugars involved was revealed by a receptor "pre-saturation" strategy in which sugars fed to the mosquitoes inhibited normal host-parasite interactions.</p> <p>Methods</p> <p><it>Anopheles stephensi </it>mysorensis mosquitoes were artificially infected with <it>P. vivax </it>by feeding on the blood of gametocytaemic volunteers reporting to local malaria clinics in the Sistan-Baluchistan province of south-eastern Iran. In order to determine the inhibitory effect of carbohydrates on sporogonic development, vector mosquitoes were allowed to ingest blood meals containing both gametocytes and added carbohydrates. The carbohydrates tested were GlcNAc, GalNAc, arabinose, fucose, mannose, lactose, glucose and galactose. Sporogonic development was assessed by survival of the parasite at both the oocyst and sporozoite stages.</p> <p>Results</p> <p>Oocyst development was observed among nearly 6% of the fed control mosquitoes but the overall number of mosquitoes exhibiting sporozoite invasion of the salivary glands was 47.5% lower than the number supporting oocysts in their midgut. Of the tested carbohydrates, only arabinose and fucose slightly perturbed the development of <it>P. vivax </it>oocysts at the basal side of the mosquito midgut, and the remaining sugars caused no reductions in oocyst development. Strikingly however, sporozoites were completely absent from the salivary glands of mosquitoes treated with mannose, GalNAc, and lactose.</p> <p>Conclusion</p> <p>The study indicates that <it>An. stephensi </it>in southern Iran has the potential to survive long enough to be re-infected and transmit vivax malaria several times, based on the average adult female longevity (about 30 days) and its gonotrophic cycle (2–3 days) during the malaria transmission season. Certain sugar binding interactions are important for the development of <it>P. vivax </it>sporozoites, and this information may be instrumental for the development of transmission blocking strategies.</p

The dominant Anopheles vectors of human malaria in the Asia-Pacific region: occurrence data, distribution maps and bionomic précis

<p>Abstract</p> <p>Background</p> <p>The final article in a series of three publications examining the global distribution of 41 dominant vector species (DVS) of malaria is presented here. The first publication examined the DVS from the Americas, with the second covering those species present in Africa, Europe and the Middle East. Here we discuss the 19 DVS of the Asian-Pacific region. This region experiences a high diversity of vector species, many occurring sympatrically, which, combined with the occurrence of a high number of species complexes and suspected species complexes, and behavioural plasticity of many of these major vectors, adds a level of entomological complexity not comparable elsewhere globally. To try and untangle the intricacy of the vectors of this region and to increase the effectiveness of vector control interventions, an understanding of the contemporary distribution of each species, combined with a synthesis of the current knowledge of their behaviour and ecology is needed.</p> <p>Results</p> <p>Expert opinion (EO) range maps, created with the most up-to-date expert knowledge of each DVS distribution, were combined with a contemporary database of occurrence data and a suite of open access, environmental and climatic variables. Using the Boosted Regression Tree (BRT) modelling method, distribution maps of each DVS were produced. The occurrence data were abstracted from the formal, published literature, plus other relevant sources, resulting in the collation of DVS occurrence at 10116 locations across 31 countries, of which 8853 were successfully geo-referenced and 7430 were resolved to spatial areas that could be included in the BRT model. A detailed summary of the information on the bionomics of each species and species complex is also presented.</p> <p>Conclusions</p> <p>This article concludes a project aimed to establish the contemporary global distribution of the DVS of malaria. The three articles produced are intended as a detailed reference for scientists continuing research into the aspects of taxonomy, biology and ecology relevant to species-specific vector control. This research is particularly relevant to help unravel the complicated taxonomic status, ecology and epidemiology of the vectors of the Asia-Pacific region. All the occurrence data, predictive maps and EO-shape files generated during the production of these publications will be made available in the public domain. We hope that this will encourage data sharing to improve future iterations of the distribution maps.</p

"Role of Lectins in Interaction Between Parasites and the Important Insect Vectors"

There is growing evidence that lectin-carbohydrate interactions can mediate the infection of parasites to their insect vector. Many insect species are host or vectors of protozoan or metazoan parasites that cause socially and economically important disease such as malaria and leishmaniasis. However, relatively little work has been undertaken concerning the interaction of insect immunity against parasite invasion with respect to lectins activities. Both immune defences (cellular and noncellular) of insect haemolymph react in order to combat the diverse array of natural pathogens and other microorganisms. The most of immune substances are innate, naturally-occurring and nonspecific molecules present in haemolymph. When the physical defences of the insect gut or integument are breached by an invading organism an innate response begins, characterized by immune system&apos;s agents such as coagulation, melanization, phagocytosis, encapsulation and nodule formation. Nevertheless, in many cell types such as insect haemocytes, carbohydrates are known to be crucially involved in cell-cell interactions and many studies have addressed the role of carbohydrates and carbohydratebinding molecules in the adhesion of parasites to their host. As mentioned above, one candidate for attachment and invasion may be lectins or lectinlike molecules that are known to mediate cell-to-cell interaction. In order to the basic understanding of pathogens transmission by vectors, in this article, the interaction between parasites and insect vectors has been reviewed with respect to role of lectins molecules

Mosquito Vector Biting and Community Protection in a Malarious Area, Siahoo District, Hormozgan, Iran

&quot;nAbstract &quot;nBackground: Use of bed-net continues to offer potential strategy for malaria prevention in endemic areas. Local communi&amp;shy;ties are indispensable during design and implementation stages. &quot;nMethods: A cross-sectional study of 192 randomly selected inhabitants was carried out in malarious zone, Siahoo dire&amp;shy;strict, Hormozgan Province, southern Iran. In addition, we monitored human landing periodicity of main malaria vec&amp;shy;tors and as well as self-protection of inhabitant in the study area for a period of one transmission season between April to October 2006. &quot;nResults: The biting activities were seen throughout the whole night for three malaria vectors, Anopheles fluviatilis, An. stephensi and An. Dthali, and&amp;nbsp; An. fluviatilis exhibiting bimodal peaks, the first at midnight (0:00-1:00) and the other before dawn (5:00&amp;minus;6:00 am) but the maximum biting activity of An. stephensi was occurred at second quarter of night (11:00-12:00 pm). The majority of interviewers (83.3%) knew that malaria was transmitted by mosquitoes and 70.3% of them stated that bed-net is the best control measures. Most subjects (62%) did not have a mosquito net. &quot;nConclusion: Study subjects were aware of an association between mosquito bite and malaria transmission. Health work&amp;shy;ers at different levels of the health care delivery system should disseminate relevant information about self-protection to help community members to be involved more in malaria control. &quot;n&amp;nbsp; &quot;nKey words: Malaria, Community Protection, Mosquito Bite, Ira

Anthropophily of Malaria Vectors in Kahnouj District, South of Kerman, Iran

This study was conducted to investigate hematophagic tendencies of the malaria vector based on a seasonal basis as well as by geographical region in a malaria endemic area in Kahnouj, southern Iran. This study was carried out for 14 months from Apr/ 2002 up to the end of May 2003. Female anophelines were collected from different shelters in hilly and plain regions of Kahnouj district and their blood meal was tested using ELISA test methods. The five vectors that were active in the study area consisted of An. fluviatilis, An. stephensi, An. dthali, An. culicifacies, and An. superpictus. The dominant Anopheline in hilly areas was An. fluviatilis sibling species T. This species was active during whole year and reached a peak in December. In contrast the dominant species in flat regions was An. stephensi which showed strongly endophilic behavior with two seasonal activity peaks. The anthropophilic index for An. fluviatilis and An. stephensi was estimated at 2.68% and 0.5%, respectively. The population of other species was too low and they did not show a propensity for human blood. The most malaria cases occurred in the hilly area where An. fluviatilis is the active dominant species. It seems that An. fluviatilis is responsible for transmission of malaria in hilly districts of Kahnouj. Thus malaria transmission in this study area is much influenced by resident’s rest habits while a wild vector, An. fluviatilis shows exophilic behavior and uses microclimate shelters with high incidence of human blood feeding. Thus, adapting people to use personal protection such as a bed net instead of residual spraying may be considered as an effective measure in malaria control in hilly regions

Comparative Susceptibility of Different Biological Forms of Anopheles stephensi to Plasmodium berghei ANKA Strain

BACKGROUND: There are varying degrees of compatibility between malaria parasite-mosquito species, and understanding this compatibility may be crucial for developing effective transmission-blocking vaccines. This study investigates the compatibility of different biological forms of a malaria vector, Anopheles stephensi, to Plasmodium berghei ANKA strain. METHODS: Several biologically different and allopatric forms of A. stephensi were studied. Three forms were isolated from different regions of southern Iran: the variety mysorensis, the intermediate form and the native type form, and an additional type form originated from India (Beech strain).The mosquitoes were experimentally infected with P. berghei to compare their susceptibility to parasitism. Anti-mosquito midgut antiserum was then raised in BALB/cs mice immunized against gut antigens from the most susceptible form of A. stephensi (Beech strain), and the efficacy of the antiserum was assessed in transmission-blocking assays conducted on the least susceptible mosquito biological form. RESULTS: The susceptibility of different biological forms of A. stephensi mosquito to P. berghei was specifically inter-type varied. The Beech strain and the intermediate form were both highly susceptible to infection, with higher oocyst and sporozoite infection rates than intermediate and mysorensis forms. The oocyst infection, and particularly sporozite infection, was lowest in the mysorensis strain. Antiserum raised against midgut proteins of the Indian Beech type form blocked infection in this mosquito population, but it was ineffective at blocking both oocyst and sporozoite development in the permissive but geographically distant intermediate form mosquitoes. This suggests that a strong degree of incompatibility exists between the mosquito strains in terms of midgut protein(s) acting as putative ookinete receptors. CONCLUSIONS: The incompatibility in the midgut protein profiles between two biological forms of A. stephensi demonstrates a well-differentiated population structure according to geographical origin. Therefore, the design of potential transmission-blocking strategies should incorporate a more thorough understanding of intra-species variations in host-parasite interactions