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

Intensity of <i>Plasmodium berghei</i> oocyst infection per midgut in different biological forms of <i>Anopheles stephensi</i>.

<p>All batches of mosquitoes were artificially fed on BALB/c blood with equalized parasitaemas. Each dot represents the number of oocysts in an individual midgut, and the graph shows pooled data from four experiments. The horizontal bars indicate median infection intensity. Asterisks denote significant differences at <i>p</i><0.05 between the different mosquito forms (Mann-Whitney non-parametric t-test). The pooled data exhibit significantly different variances. Additional analyses were performed (by Kruskal-Wallis 1-way ANOVA with Dunn's multiple comparisons post test) on log-transformed oocyst counts from infected midguts (ignoring uninfected midguts), and did not find significant differences between the mosquito types.</p

Effects of anti-mosquito midgut antiserum on the prevalence of <i>P. berghei</i> oocysts and sporozoites in two populations of <i>A. stephensi</i>.

<p>Antiserum was raised against midgut antigens from the Beech type form <i>of A. stephensi</i> and then a mixture of antiserum and <i>P. berghei</i> were fed to both the Beech type form and to intermediate form mosquitoes. The bars represent the percentage of fed mosquitoes exhibiting (a) oocysts in their midguts, and (b) sporozoites in their salivary glands. The mean of three replicate experiments is presented, +/− SEM. Asterisks denote significance at <i>p</i><0.05 (calculated by the Mann-Whitney non-parametric t-test).</p

Prevalence of <i>Plasmodium berghei</i> sporozoites in different biological forms of <i>Anopheles stephensi</i>.

<p>All batches of mosquitoes were artificially fed on BALB/c blood with equalized parasitaemas. The percentage of fed mosquitoes with sporozoites formation in their salivary glands was then determined. Each bar represents the geometric mean of four experiments, +/−95% confidence intervals (<i>n</i> = 4; each experiment included 17–24 fed mosquitoes per test group). Asterisk denotes significance (P = 0.0286, non-parametric Mann-Whitney t-test).</p

Prevalence of <i>Plasmodium berghei</i> oocysts in different biological forms of <i>Anopheles stephensi</i>.

<p>All batches of mosquitoes were artificially fed on BALB/c blood with equalized parasitaemas. The percentage of fed mosquitoes exhibiting oocyst formation in their midguts was then determined. Each bar represents the geometric mean of four experiments, +/− 95% confidence intervals (<i>n</i> = 4; each experiment included 17–24 fed mosquitoes per test group). There were no significant differences in oocyst prevalence between the forms of mosquito.</p

Competency of mysorensis strain for and the role of inhibitory carbohydrates to block its sporogonic cycle-1

as the mean of three independent experiments. For each of the three developmental stages, the number of insects containing parasites in each treatment group was statistically compared with the corresponding control using the Chi Squared test (* P < 0.05). Numbers in parentheses refer to the sample size (n), i.e. total number of engorged insects.<p><b>Copyright information:</b></p><p>Taken from "Competency of mysorensis strain for and the role of inhibitory carbohydrates to block its sporogonic cycle"</p><p>http://www.malariajournal.com/content/7/1/131</p><p>Malaria Journal 2008;7():131-131.</p><p>Published online 15 Jul 2008</p><p>PMCID:PMC2500038.</p><p></p

Competency of mysorensis strain for and the role of inhibitory carbohydrates to block its sporogonic cycle-0

Staining.<p><b>Copyright information:</b></p><p>Taken from "Competency of mysorensis strain for and the role of inhibitory carbohydrates to block its sporogonic cycle"</p><p>http://www.malariajournal.com/content/7/1/131</p><p>Malaria Journal 2008;7():131-131.</p><p>Published online 15 Jul 2008</p><p>PMCID:PMC2500038.</p><p></p

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