Brugia malayi microfilariae (Nematoda: Filaridae) enhance the infectivity of Venezuelan equine encephalitis virus to Aedes mosquitoes (Diptera: Culicidae).
01 Nov 1999-Journal of Medical Entomology (Entomological Society of America)-Vol. 36, Iss: 6, pp 758-763
TL;DR: The contrasting effects of microfilarial enhancement of viral infectivity and MF-induced mortality in mosquitoes differed among mosquito species and were determined by the nature and consequences of MF penetration through the mosquito midgut, but not to differences in mosquito susceptibilities to parenterally introduced virus.
Abstract: We examined the potentially conflicting effects that microfilarial ( MF) enhancement of viral infectivity and MF-induced mortality in mosquitoes have on the vectorial capacity of Aedes aegypti (L.), Aedes triseriatus (Say), and Aedes taeniorhynchus (Wiedemann) for Venezuelan equine encephalitis virus (VEE) when mosquitoes feed on gerbils co-infected with Brugia malayi (Buckley). Groups of mosquitoes were fed on gerbils that were either dually infected (VEE plus B. malayi MF) or singly infected (VEE only). Mosquito mortality was recorded daily, and 5-8 d later, surviving mosquitoes were assayed for disseminated viral infection. The contrasting effects of MF enhancement and MF-induced mortality differed among mosquito species and were determined by the nature and consequences of MF penetration through the mosquito midgut, but not to differences in mosquito susceptibilities to parenterally introduced virus. In Ae. aegypti, MF-induced mortality was high and tended to eliminate any significant effect of MF enhancement. In Ae. triseriatus, MF-induced mortality was low, and feeding on dually infected hosts resulted in 9 times as many mosquitoes with disseminated viral infections as did feeding on singly-infected hosts. In Ae. taeniorhynchus, MF-induced mortality was extremely high, yet under our experimental conditions, feeding on a dually infected hosts resulted in nearly 30 times as many disseminated infections as did feeding on singly infected hosts. The final outcome on vectorial capacity depended on the specific combination of MF, virus, and mosquito species involved. Therefore, future efforts toward understanding MF enhancement should be directed toward mosquito-virus-parasite species combinations that occur together in nature.
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TL;DR: The understanding of the interplay between mosquitoes and the immune system of their hosts is still in its infancy, but it is clear that there is great potential for exploiting this interplay in the control of mosquito‐borne diseases.
Abstract: The intimate contact between mosquitoes and the immune system of their hosts is generally not considered important because of the transient nature of mosquito feeding. However, when hosts are exposed to many feeding mosquitoes, they develop immune responses against a range of salivary antigens. Understanding the importance of these responses will provide new tools for monitoring vector populations and identifying individuals at risk of mosquito-borne diseases, and allow the development of novel methods for monitoring control and mosquito-release programmes. Antibodies targeting the mosquito midgut are also important in the development of mosquito vaccines. The feasibility of this approach has been demonstrated and future research opportunities are considered in this review. The potential impact of mosquito vaccines is also discussed. Our understanding of the interplay between mosquitoes and the immune system of their hosts is still in its infancy, but it is clear that there is great potential for exploiting this interplay in the control of mosquito-borne diseases.
77 citations
TL;DR: A series of recombinant alphaviruses, based upon the genome of ONNV, designed for the expression of heterologous genes, that will be a valuable asset in parasite–mosquito interaction and interference research and to serve as tools for antimalaria studies.
Abstract: Arthropod-borne alphaviruses transmitted by mosquitoes almost exclusively use culicines; however, the alphavirus o'nyong-nyong (ONNV) has the unusual characteristic of being transmitted primarily by anopheline mosquitoes This unusual attribute makes ONNV a valuable tool in the characterization of mosquito determinants of infection as well as a useful expression system in Anopheles species We developed a series of recombinant alphaviruses, based upon the genome of ONNV, designed for the expression of heterologous genes The backbone genome is a full-length infectious cDNA clone of ONNV from which wild-type virus can be rescued Additional constructs are variants of the primary clone and contain the complete genome plus a duplicated subgenomic promoter element with a multiple cloning site for insertion of heterologous genes We inserted a green fluorescent protein (GFP) gene downstream of this promoter and used it to characterize infection and dissemination patterns of ONNV within An gambiae mosquitoes These experiments allowed us to identify atypical sites of initial infection and dissemination patterns in this mosquito species not frequently observed in comparable culicine infections The utility of these ONNVs for studies in anopheline mosquitoes includes the potential for identification of vector infection determinants and to serve as tools for antimalaria studies Viruses that can express a heterologous gene in a vector and rapidly and efficiently infect numerous tissues in An gambiae mosquitoes will be a valuable asset in parasite-mosquito interaction and interference research
68 citations
Cites background from "Brugia malayi microfilariae (Nemato..."
...taeniorhynchus coinfected with microfilariae (Vaughan & Turell, 1996a; Vaughan et al., 1999)....
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...Disseminated VEE and EEE virus infections were also found up to thirty times more frequently in Ae. taeniorhynchus coinfected with microfilariae (Vaughan & Turell, 1996a; Vaughan et al., 1999)....
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TL;DR: The alterations in mosquito feeding propensity reported here would occur if parasites have been selected to make infected vertebrate hosts more attractive to mosquitoes, and infected mosquitoes are more likely to seek out new blood meals.
Abstract: Arthropod vectors of disease may encounter more than one infected host during the course of their lifetime. The consequences of super-infection to parasite development are rarely investigated, but may have substantial epidemiological and evolutionary consequences. Using a rodent malaria model system, behavioural avoidance of super-infection was tested by examining whether already-infected Anopheles stephensi mosquitoes were less responsive to new vertebrate hosts if they were infected. Additionally, a second dose of parasites was given to malaria-infected mosquitoes on a biologically realistic time scale to test whether it impeded the development of a first infection. No effect of a second infected blood meal on either the prevalence or parasite burden arising from a first was found. Furthermore, it was found that not only were infected mosquitoes more likely to take a second blood meal than their uninfected counterparts, they were disproportionately drawn to infected hosts. The alterations in mosquito feeding propensity reported here would occur if parasites have been selected to make infected vertebrate hosts more attractive to mosquitoes, and infected mosquitoes are more likely to seek out new blood meals. Although such a strategy might increase the risk of super-infection, this study suggests the cost to parasite development is not high and as such would be unlikely to outweigh the potential benefits of increasing the contact rate between the parasite's two obligate hosts.
58 citations
Cites background from "Brugia malayi microfilariae (Nemato..."
...For example, in the laboratory, pathogen transmission can be enhanced when different parasite species co-occur in the same individual vector, a phenomenon that has been observed in some [1-4] but not all mosquito species that have been tested [1,4]....
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TL;DR: Eleven species were evaluated from Florida to determine which of these species should be targeted for control should Rift Valley fever virus (RVFV) be detected in North America and how environmental factors affect transmission.
Abstract: We evaluated Aedes atlanticus Dyar and Knab, Aedes infirmatus Dyar and Knab, Aedes vexans (Meigen), Anopheles crucians Wiedemann, Coquillettidia perturbans (Walker), Culex nigripalpus Theobald, Mansonia dyari Belkin, Heinemann, and Page, and Psorophora ferox (Von Humboldt) from Florida to determine which of these species should be targeted for control should Rift Valley fever virus (RVFV) be detected in North America. Female mosquitoes that had fed on adult hamsters inoculated with RVFV were incubated for 7-21 d at 26 degrees C, then allowed to refeed on susceptible hamsters, and tested to determine infection, dissemination, and transmission rates. We also inoculated mosquitoes intrathoracically, held them for 7 d, and then allowed them to feed on a susceptible hamster to check for a salivary gland barrier. When exposed to hamsters with viremias > or = 10(7.6) plaque-forming units per milliliter of blood, at least some individuals in each of the species tested became infected; however, Cx. nigripalpus, An. crucians, and Ae. infirmatus were essentially incompetent vectors in the laboratory because of either a midgut escape or salivary gland barrier. Each of the other species should be considered as potential vectors and would need to be controlled if RVFV were introduced into an area where they were found. Additional studies need to be conducted with other geographic populations of these species and to determine how environmental factors affect transmission.
52 citations
Cites background from "Brugia malayi microfilariae (Nemato..."
...Similar examples of microÞlarial enhancement have been shown with other mosquito and virus and Þlarial worm combinations (Turell et al. 1987, Vaughan et al. 1999)....
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TL;DR: Evidence indicates the existence of a salivary gland infection barrier in Anopheles stephensi and the basal lamina may prevent access to mosquito cell surface virus receptors and help explain why anopheline mosquitoes are relatively incompetent arbovirus transmitters when compared to culicines.
Abstract: Knowledge of the fate of an arbovirus in a mosquito is fundamental to understanding the mosquito’s competence to transmit the virus When a competent mosquito ingests viremic vertebrate blood, virus infects midgut epithelial cells and replicates, then disseminates to other tissues, including salivary glands and/or ovaries The virus is then transmitted to the next vertebrate host horizontally via bite and/or vertically to the mosquito’s offspring Not all mosquitoes that ingest virus become infected or, if infected, transmit virus Several “barriers” to arbovirus passage, and ultimately transmission, have been identified in incompetent or partially competent mosquitoes, including, among others, gut escape barriers and salivary gland infection barriers The extra-cellular basal lamina around the midgut epithelium and the basal lamina that surrounds the salivary glands may act as such barriers Midgut basal lamina pore sizes are significantly smaller than arboviruses and ultrastructural evidence suggests that midgut tracheae and tracheoles may provide a means for viruses to circumvent this barrier Further, immunocytochemical evidence indicates the existence of a salivary gland infection barrier in Anopheles stephensi The basal lamina may prevent access to mosquito cell surface virus receptors and help explain why anopheline mosquitoes are relatively incompetent arbovirus transmitters when compared to culicines
49 citations
References
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TL;DR: Life table statistics were used to examine the survival functions of filarial susceptible and refractory species of the Aedes scutellaris (Walker) group of mosquitoes, following infection with high and moderate doses of Brugia pahangi.
Abstract: . . Life table statistics were used to examine the survival functions of filarial susceptible and refractory species of the Aedes scutellaris (Walker) group of mosquitoes, following infection with high and moderate doses of Brugia pahangi (Buckley & Edeson). Survivorship curves and hazard function curves were generated, and the median survival times and the proportions of mosquitoes surviving beyond the extrinsic incubation period of the parasite were determined.
In the susceptible populations of Aedes polynesiensis Marks, Ae.pseudo-scutellaris (Theobald) and Ae. tabu Ramalingam & Belkin a dose-response relationship was detected between parasite load and mortality. This relationship was characterized by a significant reduction in the proportions of infected female mosquitoes surviving at days 1 and 9 postinfection, reduction in the median survival times and an increase in the hazard rates as the infectious dose increased.
The survival of the refractory species, Ae.alcasidi Huang and Ae.katherinensis Woodhill was not significantly affected by the infection. A positive correlation between microfilaraemia in the vertebrate host and parasite load in the susceptible mosquito populations was also observed.
Regression analysis of the number of parasites recovered from susceptible mosquitoes at the time of death showed that mosquitoes at highest risk of dying harboured from 11.6 to 19.4 infective larvae when fed on a gerbil with sixty-five microfilariae per 20,μl blood; this resulted in 34.4–40.2% mortality by day 9 postinfection. A mean number of 32.6–46.9 infective larvae was observed when these populations were exposed to a gerbil with a microfilaraemia of 150 mf/20 μl and resulted in 72.8% to 80% mortality in these populations. Viable infective larvae were recovered from infected mosquitoes up to 50 days postinfection.
11 citations
TL;DR: A study of Mansonella perstans filariasis conducted in the Chaillu mountains, Southern Congo, showed that 108 of 134 Pygmies and 79 of 302 Bantus presented with microfilaraemia.
Abstract: A study of Mansonella perstans filariasis conducted in the Chaillu mountains, Southern Congo, showed that 108 of 134 Pygmies (80·6%) and 79 of 302 Bantus (26·2%) presented with microfilaraemia. The...
9 citations
TL;DR: Monanema nilotica n.sp.
Abstract: Monanema nilotica n.sp. (Nematoda: Onchocercidae) is described from the right auricle and pulmonary artery of the Nile rat, Arvicanthis niloticus testicularis (Sundevall, 1842), trapped in Khartoum-North, Sudan. It differs from other species principally in length of adults and microfilariae, in the shape of the buccal capsule and in the structure of the spicules of the males.
7 citations
TL;DR: During the course of studies on human filariasis in Fiji in the period 1954–50, two new microfilariae were found in fruit bats.
Abstract: During the course of studies on human filariasis in Fiji in the period 1954–50, two new microfilariae were found in fruit bats. The first was found in the blood of 38 bats out of 111 examined from various islands of the territory. It has recently been described and named Microfilaria fijiensis by Yeh, Symes and Mataika (1958).
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