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PubMed2004

The impact of ivermectin treatment alone and when in parallel with Simulium neavei elimination on onchocerciasis in Uganda.

The study was conducted in August 2002 in Kigoyera parish in Kyenjojo district, where ivermectin treatment had been the strategy to control onchocerciasis since 1991 and was later supplemented with Simulium neavei control in 1995 and subsequent elimination; and in July 2003 in Kicece parish in Kamwenge district, where ivermectin treatment alone had been the strategy used to control onchocerciasis since 1991. Our objective was to examine and compare the impact of ivermectin treatment alone and when in parallel with S. neavei elimination on nodule and microfilariae carrier rates and on onchocercal dermatitis to provide baseline data that could be used to monitor the trends of microfilariae carrier rates for decision-making on when to discontinue ivermectin treatment. The combined interventions had significantly reduced onchocercal dermatitis from 34% pre-control to 2.9% (P < 0.001), microfilariae carrier rate from 88 to 7.5% (P < 0.001) and nodule prevalence from 49 to 19.2% (P < 0.001). Ivermectin treatment alone had also reduced onchocercal dermatitis prevalence from 34.2% pre-control to 9.5% (P < 0.001), the microfilariae carrier rate from 78 to 27.8% (P < 0.001) and nodule prevalence from 49.1 to 14.2% (P < 0.001). None of the children under 10 years were nodule or microfilariae carriers in both study areas. Histological examination of eight nodules extirpated from patients in Kigoyera identified five male and 12 female adult worms that were all old and alive. Five live and one dead female worms and one live male worm were identified from nodules extirpated from patients in Kicece. There was no female worm with embryogenesis from the nodules obtained from Kigoyera while two female worms from five nodules obtained from Kicece still showed a few embryos. Two female worms in each of the study area had sperms in uteri indicating that male worms were still active. Ivermectin treatment in parallel with vector elimination had a greater impact on onchocercal dermatitis and microfilariae carrier rates than ivermectin treatment alone. It would be worthwhile considering supplementation of ivermectin treatment with vector elimination in all isolated foci with S. neavei transmission to hasten the elimination of onchocerciasis as a public health and socio-economic problem in those foci.

Adolescent↗
PubMed2006

Cytogenetic and PCR-based identification of S. damnosum "Nkusi J" as the anthropophilic blackfly in the Uluguru onchocerciasis focus in Tanzania.

A combined molecular and cytogenetic analysis was used to identify the local blackfly vectors of onchocerciasis in the Uluguru Mts. focus, Morogoro region, central Tanzania. Cytotaxonomic identification revealed the occurrence of three cytospecies of the Simulium damnosum complex, along altitudinal gradients. The cytoform "Nkusi" was found breeding at low to mid-altitudes (100-500 m), while S. kilibanum was found at mid- and high altitudes (300-1260 m), being sympatric with "Sebwe" only in the highlands. The analyses further revealed the cytoform "Nkusi" from the nearby Kilosa focus. Simulium kilibanum and "Nkusi" are potential vectors of onchocerciasis, while the "Sebwe" form is considered non-anthropophilic and therefore not a vector. By means of molecular typing of wild-caught females, "Nkusi" was incriminated as the man-biting fly at all catching sites, and consequently, is the assumed vector of onchocerciasis over the full altitude range. In the high altitude zones, however, S. neavei group species may act as secondary vectors at the edge of the forest reserve, if transmission actually occurs there at all. Our results also suggest that vector control could be feasible because of the vector species breeding in the foothills below 500 m in relatively accessible open country.

Altitude↗
PubMedDate not supplied

Sporogonic development of Leucocytozoon smithi.

The sporogonic development of Leucocytozoon smithi in its black fly vector was studied by light and electron microscopy and was compared with that of other haemosporidians. Within 18 to 24 h after ingestion of gametocytes by black flies, ookinetes passing through the midgut epithelium were observed. Intracellular migration of ookinetes resulted in the apparent disruption and degeneration of host cells. Intercellular migration also occurred as was evidenced by the presence of ookinetes between midgut cells. Transformation of ookinete to spherical oocyst occurred extracellularly in three different sites. Although most oocysts were found between the host cell basal membrane and the basal lamina, large numbers also were found attached to the external surface of the basal lamina, projecting into the hemocoel. Ectopic development of oocysts in the midgut epithelium between cells was observed much less frequently than development on the basal side of the midgut. The oocyst wall of dense granules, believed to be of parasite origin, was distinguishable from the basal lamina of the host's midgut epithelium. As in other Leucocytozoidae, the cytoplasm of the oocyst differentiated into a single sporoblastoid from which 30-50 sporozoites were formed. Beginning on the third day post infection, elongation of segregated dense sporoblastoid material associated with pellicle thickening led to the formation of the finger-like sporozoite buds which projected into the oocyst cavity. Sporozoites within mature oocysts and salivary glands were structurally similar to sporozoites as described for other haemosporidians.

Animals↗
PubMedDate not supplied

Schizogonic development of Leucocytozoon smithi.

The schizogonic development of Leucocytozoon smithi in the liver of experimentally infected turkey poults was examined by electron microscopy. Following intraperitoneal injection, sporozoites migrated to the liver and entered hepatic cells to become intracellular trophozoites. Three to four days post inoculation (PI), trophozoites underwent asexual multiple fission known as merogony or schizogony. Two generations of schizonts were observed. The primary or first generation schizonts, abundant on day 4 PI, appeared as interconnected cytoplasmic masses (pseudocytomeres). Each pseudocytomere was enclosed by a membranous vacuole and contained varying numbers of nuclei. As nuclear division and growth of the schizonts continued, larger discrete cytoplasmic masses or cytomeres were formed with rhoptries and multiple nuclei in various stages of division. Synchronous multiple cytoplasmic cleavage of the schizont resulted in the formation of numerous uninucleate merozoites. Second generation schizonts, which developed from hepatic merozoites released from primary schizonts, were abundant in hepatocytes on day 6 PI. Although tissue samples from liver, lung, spleen, kidney, intestine, brain, blood vessels and lymph nodes were examined, schizogonous forms were observed in liver only. No megaloschizonts were detected in any host tissue examined. Schizogonic development was completed by day 7 PI as merozoites developed into gametocytes within mononuclear phagocytes.

Animals↗
PubMedDate not supplied

Gametogenesis, fertilization and ookinete differentiation of Leucocytozoon smithi.

Development of Leucocytozoon smithi during gametogenesis, fertilization, and ookinete differentiation was studied by light and electron microscopy. Gametogenesis occurred rapidly, within 1-2 min after gametocytes were ingested by black flies. Usually one axoneme, but not infrequently two, was observed in microgametes. The macrogamete nucleus was characteristically elongated and fragmented, with a convoluted nuclear envelope. Fertilization occurred within five min after ingestion of gametocytes by the vector. The entire axoneme and nucleus of the microgamete entered the cytoplasm of the macrogamete. Zygote differentiation resembled sporozoite formation in that a thickened inner membrane and subpellicular microtubules developed beneath the plasmalemma, followed by cytoplasmic protrusion or evagination to form the anterior end. Extension of the inner thickened membrane continued as the zygote elongated. Development of sausage-shaped ookinetes was completed within 6-8 h after ingestion of a blood meal by a black fly. Mature ookinetes possessed a single nucleus, double-layered pellicle, canopy, apical pore, polar ring complex, subpellicular microtubules, micronemes, crystalloids, abundant mitochondria, endoplasmic reticulum, and ribosomes. Comparison of development of L. smithi with species of Plasmodium and Haemoproteus revealed general similarities in both sexual and asexual development within the insect vector. A diagram summarizing life cycle events for L. smithi is included.

Animals↗
PubMedDate not supplied

Development of the insect pathogenic alga Helicosporidium.

This study examined the morphogenesis and replication dynamics of the different life stages (cysts, filamentous cells, vegetative cells) of Helicosporidium sp., a non-photosynthetic, entomopathogenic alga. The isolate (SjHe) used originated from an infected black fly larva. Filamentous cell transformation into vegetative cells and autosporulation during vegetative cell replication were observed under controlled in vitro conditions. The transformation process was initiated by a partial swelling of the filamentous cell along with the reorganization of the nuclear material. Two subsequent nuclear and cell divisions resulted in the release of 4 rod-shaped daughter cells, which divided into oval to spherical vegetative cells. These underwent several cycles of autosporogenic cell division. Multiple-passaged vegetative cell cultures formed non-motile, adherent cell clusters (palmelloid colonies). Vegetative replication dynamics were also observed in 2 experimental noctuid hosts, Spodoptera exigua and Helicoverpa zea. The average density of helicosporidial cells produced per microliter hemolymph exceeded cell concentrations obtained in vitro by 15- and 46-fold in S. exigua and H. zea, respectively. Cyst morphogenesis was only observed in the hemolymph, whereas no cysts differentiated at various in vitro conditions.

Animals↗
PubMed2002

Immunolocalization of vesicular stomatitis virus in black flies (Simulium vittatum).

Vesicular stomatitis, a disease of cattle, horses, and swine, is caused by either vesicular stomatitis virus, New Jersey serotype (VSV-NJ), or vesicular stomatitis virus, Indiana serotype, which are related viruses in the genus Vesiculovirus, family Rhabdoviridae. Although recognized for at least 160 years, the epidemiology and pathogenesis of this disease remains undefined. Black flies have been suggested as a vector for VSV-NJ. In this study we infected three- to four-week-old female black flies with VSV-NJ via feeding of virus-spiked ox blood or intrathoracic inoculation, and demonstrated the location of virus by immunohistochemistry. These preliminary findings suggest that VSV-NJ initially infects the gut in the natural situation but that subsequent spread to the salivary gland may be blocked in older flies, decreasing their ability to transmit the virus. The pattern of staining was different in intrathoracic inoculated flies. In these flies, salivary gland involvement was more likely, and extensive staining of eye, brain, and hemolymph suggested a more generalized infection that apparently circumvented the gut. We conclude that intrathoracic inoculation may be an inappropriate method of infection for determining vector competence and that the age of the vector should be considered when conducting competency studies.

Animals↗
PubMed1983

Equine onchocerciasis in Queensland and the Northern Territory of Australia.

Investigations were conducted on the taxonomy, distribution in the carcase, pathology and transmission of Onchocerca spp. in equids from Queensland and the Northern Territory. Examination of small groups of horses and ponies revealed high infection rates with O. cervicalis, while lesser numbers were infected with O. gutturosa. O. reticulata was not found. Neither of the Australian species is likely to be of economic importance to the horsemeat industry. The findings support the belief that O. cervicalis is a pre-disposing factor in the aetiology of equine nuchal disease, most commonly seen clinically as fistulous withers. O. gutturosa is virtually non-pathogenic. Forcipomyia (Lasiohelea) townsvillensis, Austrosimulium pestilens and Culicoides victoriae are suggested as potential vectors, and it is unlikely that C. brevitarsis is involved.

Animals↗
PubMed2000

Transmission of vesicular stomatitis virus from infected to noninfected black flies co-feeding on nonviremic deer mice.

Vesicular stomatitis is an economically important arboviral disease of livestock. Viremia is absent in infected mammalian hosts, and the mechanism by which insects become infected with the causative agents, vesicular stomatitis viruses, remains unknown. Because infected and noninfected insects potentially feed on the same host in nature, infected and noninfected black flies were allowed to feed on the same host. Viremia was not detected in the host after infection by a black fly bite, but because noninfected black flies acquired the virus while co-feeding on the same host with infected black flies, it is concluded that a viremic host is not necessary for an insect to be infected with the virus. Thus co-feeding is a mechanism of infection for an insect-transmitted virus.

Animals↗
PubMed1986

The effects of ivermectin on transmission of Onchocerca volvulus.

Ivermectin, given to onchocerciasis patients as a single oral dose of 200 micrograms per kilogram of body weight, substantially reduced the uptake of Onchocerca volvulus microfilariae by Simulium yahense, an efficient black fly vector of the parasite in the tropical rain forests of West Africa. Three months after treatment, patients given ivermectin infected flies at a significantly lower rate than those who had received diethylcarbamazine or placebo, thereby reducing the number of developing larvae in the vector population. This diminished rate of infectiousness was also evident 6 months after treatment. These results strongly suggest that ivermectin could be effective in interrupting transmission of Onchocerca volvulus for epidemiologically important periods of time.

Humans↗
PubMed1989

The role of sex chromosomes in black fly evolution.

Sex chromosomes have been repeatedly implicated in the process of speciation of black flies and other nemotocerans. Arguments are presented here against the case that frequent differences between species in their sex chromosomes are based on (i) different average rates of differentiation of sex-linked and autosomal loci or (ii) the fact that the X and Y chromosomes are less numerous than autosomal chromosomes and so are more subject to the effects of drift and the random fixation of chromosome rearrangements. The argument is made that speciation in black flies and many other groups is an adaptive process and that differentiated sex-chromosome systems play a role in this process.

Animals↗
PubMed1989

Cytological approaches to simuliid biosystematics in relation to the epidemiology and control of human onchocerciasis.

This paper presents an overview of advances in cytological research on the biosystematics of vector simuliid complexes in the areas of identification, age grading, and the evolution of resistance in relation to the epidemiology and control of human onchocerciasis. Systematic theory is discussed and relevant examples are given to show its application in predicting and resolving current problems in species identification for New World and Old World vector complexes. These complexes include Simulium damnosum s.l. and S. neavei s.l. from Africa and S. exiguum s.l., S. metallicum s.l., S. ochraceum s.l., and S. oyapockense s.l. from Latin America. The evolution of resistance in S. damnosum s.l. and the need for future molecular research as part of resistance management strategies are discussed.

Africa↗
PubMed1998

Polymorphic microsatellites in Simulium damnosum s.l. and their use for differentiating two savannah populations: implications for epidemiological studies.

In West Africa, Onchocerca volvulus, the cause of human onchocerciasis, is transmitted by sibling species of the Simulium damnosum complex. Little is known about blackfly intraspecific variability and its consequences on vectorial capacity. This study reports the use of microsatellite markers for differentiating populations of S. damnosum s.l. Five microsatellite loci were characterized and used to analyze individuals from two savannah populations in Mali, 120 km apart. Four loci were highly polymorphic, having 8-12 alleles per locus and gene diversities ranging from 77.9 to 88.2%. A significant heterozygote deficiency was observed in the two populations. This may arise from inbreeding, population structure (the Walhund effect), or the presence of null alleles. To test this last hypothesis, new primers were designed for two loci and used to analyze homozygous individuals. After correcting for null alleles, heterozygote deficit persisted. Population subdivision in the two foci remains the most likely explanation. Our results indicate that microsatellite markers could differentiate fly populations, making them valuable tools for the study of population genetic structure.

Alleles↗
PubMed1987

Visual ecology of biting flies.

Many of the similarities in visual ecology between the Nematocera and Brachycera and within the Cyclorrhapha may reflect the evolution of blood-feeding in these groups. In Nematocera and Brachycera, blood-feeding is thought to have evolved from predatory or nectar-feeding behavior (138). Only females feed on hosts, and association with hosts generally occurs when hosts are close to the aquatic or semiaquatic habitats of the immatures. Flies feed on nectar, make appetitive flights, disperse, or migrate prior to blood-feeding, and then oviposit in water. Many species are nocturnal or crepuscular. In Cyclorrhapha, flies are closely associated with hosts. They may have arisen from compost-feeding flies that developed a larval dependence on vertebrate-produced microhabitats. Both sexes blood-feed, and mating occurs on or near hosts. Flies generally emerge in the proximity of hosts and maintain close contact with them. These species are diurnal, and their visual systems are well developed. Comparisons between closely related blood-feeding and non-blood-feeding species may provide insight into the visual ecology of blood-feeding species. Despite the different origins of hematophagy, there appears to be a convergence of morphology and behavior that is related to ecology rather than to phylogenetic relationships. This is clearly seen in host-location strategies by tsetse and tabanids. Even within groups such as mosquitoes, species that are active at the same time of day and in the same habitat have more in common than closely related species in different habitats. For this reason, an ecological review would be more cohesive than this phylogenetic discussion. However, because of the disproportionate amount of literature on a small number of groups, the phylogenetic approach is the most practical for this subject. However, this review does point out the great need for research on the less well-studied groups and behaviors.

Animals↗