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PubMed1985

Studies on the biology of Simuliidae (Diptera) at the Santiago onchocerciasis focus in Ecuador, with special reference to the vectors and disease transmission.

A survey showed the presence of seven simuliid species in the onchocerciasis focus in Ecuador Simulium exiguum and S. quadrivittatum were the two most common anthropophilic species and were shown to be both experimental and natural vectors of Onchocerca volvulus. S. antillarum only occasionally bit man. Observations were made on the biology of the two vector species and it was evident that S. exiguum was the primary vector of onchocerciasis in the rainy season. The relevance of these findings to the epidemiology and control of onchocerciasis in Ecuador are discussed.

Animals↗
PubMed2005

Diurnal biting periodicity of parous Simulium (Diptera: Simuliidae) vectors in the onchocerciasis Amazonian focus.

We describe the hourly patterns of parous biting activity of the three main simuliid vectors of human onchocerciasis in the Amazonian focus straddling between Venezuela and Brazil, namely, Simulium guianense s.l. Wise; S. incrustatum Lutz, and S. oyapockense s.l. Floch and Abonnenc. Time series of the hourly numbers of host-seeking parous flies caught in five Yanomami villages during dry, rainy, and their transition periods from 1995 to 2001 were investigated using harmonic analysis (assuming an underlying circadian rhythm) and periodic correlation (based on Spearman's r). Parous S guianense s.l. showed a bimodal activity pattern, with a minor peak in mid-morning and a major peak at 16:00 h. S. incrustatum exhibited mainly unimodal activity during either early morning or midday according to locality. S. oyapockense s.l. bit humans throughout the day mainly between 10:00 and 16:00 h but also showed bimodal periodicity in some localities. Superimposed on the endogenous, species-specific daily cycles, parous activity showed variation according to locality, season, air temperature and relative humidity, with biting being promoted by warmer and drier hours during wet seasons/periods and reduced during hotter times in dry seasons or transitions. The results are discussed in terms of their implications for blackfly biology and ecology as well as onchocerciasis epidemiology and control.

Animals↗
PubMed2004

First report of a trichomycete fungus (Zygomycota: Trichomycetes) inhabiting larvae of Simulium ochraceum sensu lato Walker (Diptera: Simuliidae) from the Galapagos Islands.

A collection of the larval black fly Simulium ochraceum sensu lato Walker was made at six lotic habitats on San Cristobal Island, Galapagos Islands, Ecuador, during May 2003. Sixty-eight larvae were assayed for the presence of gut fungi (Zygomycota: Trichomycetes). A trichomycete, designated as Smittium sp. was found inhabiting the hindgut of 17.6% of S. ochraceum s.l. larvae. Implications of this finding with respect to both host and trichomycete biogeography are discussed.

Animals↗
PubMed2005

Multiple symbiotes in larval black flies (Diptera: Simuliidae): associations of trichomycete fungi with ichthyosporeans, mermithid nematodes, and microsporidia.

Studies of the interactions between two or more species of symbiotic microorganisms in a single host animal have lagged behind those involving interactions between hymenopteran or dipteran parasitoids. We screened the larvae of four species of black flies (Cnephia ornithophilia, Simulium furculatum, Simulium innoxium, and Simulium vandalicum) to determine if the colonization and prevalence of trichomycete fungi were influenced by ichthyosporeans, mermithid nematodes, microsporidia, or other species of trichomycetes. Differences in the layering of the peritrophic matrix of microsporidian-infected larvae, compared with that of uninfected larvae, were associated with greater levels of colonization by the midgut-inhabiting trichomycete Harpella melusinae. Colonization levels of different species of trichomycetes were significantly correlated with one another in only 2 of 11 cases. Aside from the consistent attachment of the trichomycete Simuliomyces microsporus to the ichthyosporean Paramoebidium chattoni, we found little evidence that prevalence and colonization levels of trichomycetes were influenced by other symbiotes, including other trichomycetes. This trend might reflect the physical separation of trichomycetes, which are gut specific, from other symbiotes. In addition, any combinations of symbiotes that were wholly incompatible would not have been observed in our field-collected material.

Amoebida↗
PubMed2006

Confirmation and identification of parasitic stages of obligate endobionts (Harpellales) in blackflies (Simuliidae) by means of rRNA sequence data.

Over the last 35y, the life cycle of endosymbiotic gut fungi (Harpellales) has been expanded to include cyst stages associated with the developing ovaries. Ovarian cysts (chlamydospore stages) have been identified after germination and production of asexual trichospores in vitro, but germination is not always successful, and spores exhibit morphological variation. Sequence data (for partial 18S and 28S rRNA genes) were generated for these putative stages of Harpellales using ungerminated cysts from adult blackflies and germinated cysts associated with field-collected blackfly egg masses. Cladistic analyses of the 18S and 28S rRNA sequences confirmed that ovarian cysts are stages in the life cycle of Harpellales. Ungerminated cysts, from a blackfly collected from New York state were identified as Pennella simulii and two samples from Newfoundland Prosimulium mixtum adults were identified as Harpella melusinae. Cysts with bipolar germ tubes, associated with field-collected Simulium egg masses from Newfoundland, were also identified as H. melusinae. Two other samples of cysts could not be matched with available sequences of gut fungi from larval hosts. The potential use of this approach to identify pathogenic stages associated with adult ovaries or field-collected egg masses among other host groups is highlighted and promoted as a tool to test the hypothesis that ovarian cysts are a dispersal stage common to all genera of Harpellales.

Animals↗
PubMed1986

Acquired resistance to Onchocerca lienalis infections in Simulium ornatum Meigen and Simulium lineatum Meigen following passive transfer of haemolymph from previously infected simuliids (Diptera, Simuliidae).

This study describes experiments which demonstrate the presence of a parasite-induced or derived factor in the haemocoel of Onchocerca lienalis-infected simuliids. Haemolymph, when transferred from previously infected donor flies to previously untreated recipient flies, using fine glass needles, confers protection against a subsequent challenge to the recipients. In three trials using Simulium ornatum sl. or S. lineatum, significant levels of protection in 'immunized' compared to 'challenge control' groups were achieved (84% and 81% with S. ornatum sl. and 85% with S. lineatum). This is despite the fact that the worm burdens of the infected donor groups in the three trials were very different (means of 33.1 and 3.4 larvae/fly with S. ornatum sl. and 1.6 larvae/fly with S. lineatum). The use of sham-operated and bentonite-inoculated control groups demonstrate that this effect is not merely a non-specific reaction to trauma, but is probably parasitic in its derivation. The use of double infections separated by 4 days shows that the donor flies have themselves probably acquired resistance to O. lienalis. Frequency distributions of O. lienalis burdens in individual flies show that there is a shift from a normal to a skew distribution when comparing 'challenge control' flies with 'immunized'. This possible acquired resistance could have important implications in the transmission of forest and savanna human onchocerciasis by the Simulium damnosum complex.

Animals↗
PubMed1994

Induction of the prophenoloxidase-activating system of Simulium (Diptera: Simuliidae) following Onchocerca (Nematoda: Filarioidea) infection.

Trials were carried out to study the humoral immune response of blackflies to filariae following infection using the intrathoracic injection technique. An induced 66 kDa protein was abundant in the haemolymph of the European species Simulium ornatum following infection with bovine Onchocerca lienalis. This protein was apparently at higher concentrations in the haemolymph of sham-inoculated flies, i.e. flies that received sterile medium without the parasites. A molecule of the same size was also observed in the haemolymph of infected S. damnosum s.l. following infection with human O. volvulus or bovine O. ochengi. However, the level of this protein was lower in blackflies injected with microfilariae of bovine O. dukei. Unlike O. volvulus and O. ochengi this species is not transmitted by S. damnosum s.l. under natural conditions. No such reaction was observed if the African blackflies had received a sham inoculation. Feeding experiments with wild-caught nulliparous S. damnosum sl. on Onchocerca-infected cattle supported the results of the injection trials. The 66 kDa protein could only be found in the haemolymph of specimens infected via a blood meal. This 66 kDa molecule was identified as phenoloxidase. It appeared in the haemolymph due to the activation of the prophenoloxidase system following the filarial infection and we hypothesize that it may be sequestered by the parasites, as part of a non-self recognition system.

Animals↗
PubMed2002

Polytene chromosomes of Simulium craigi (Diptera: Simuliidae).

Simulium craigi Adler and Currie is a polymorphic species based on polytene chromosome banding patterns in the long arm of chromosome III (IIIL). Three cytotypes are described based on the predominant IIIL sequences. These correspond to three broad geographic areas: cytotype 'CC' from Pennsylvania; cytotype 'AF' from Ontario and Manitoba; and cytotype 'ACF/BCF' from New Hampshire. In the absence of sympatric populations, these cytotype differences are best explained by clinal variation within a single species. The relationship of S. craigi to other described members of the S. vernum group is discussed.

Animals↗
PubMed1997

Molecular population studies of Simulium damnosum s.l. (Diptera: Simuliidae) using a novel interspersed repetitive DNA marker.

Simulium damnosum s.l., the vector of West African onchocerciasis, has been the target of a major insect control initiative for the past 20 years. However, attempts to study the migration patterns of reinvading infective flies into controlled areas have been restricted by the lack of suitable genetic markers. Here, the results of the first population-level study of S. damnosum s.l. using a repetitive DNA marker, pSO11, are presented. Sequence analysis of pSO11 revealed a complex internal pattern of repetition and an open reading frame with 56.8 per cent similarity to a mouse retrotransposon protein. Combined with an interspersed genomic distribution, the internal structure of pSO11 suggested that it represents the 5' half of a transposable element. The genomic diversity of the sequence was analysed using Southern blot analysis of genomic DNA. Data were collected from 475 individuals from the island of Bioko (in Equatorial Guinea), Cameroon, Côte d'Ivoire and Sierra Leone. The results indicate that pSO11 is useful as an indicator of genomic diversity and that the experimental design used here permits comparison of an approximately random sample of chromosomal loci. Making this assumption, estimates of homozygosity based on pSO11 diversity were used to study inter- and intraspecific variability. The results indicate that pSO11 is potentially useful for studying population-level processes in S. damnosum s.l.

Animals↗
PubMed2000

Molecular identification and phylogeny of East African Simulium damnosum s.l. and their relationship with west african species of the complex (Diptera: Simuliidae).

The phylogenetic relationships of East and West African members of the Simulium damnosum complex were studied by sequence analyses of the mitochondrial 16s ribosomal RNA (rRNA) gene. Results suggest that: (i) the S. damnosum complex is divided into an East and a West African clade, and (ii) S. pandanophilum and the cytoform 'Kiwira' form an East African subbranch distinct from the 'Sanje' group. In contrast to former assumptions from cytogenetic analyses, our molecular data do not support a direct relationship between the East African S. kilibanum and the West African S. squamosum. Length differences of the rDNA internal transcribed spacer 1 (ITS-1) turned out to be useful to distinguish between cytoforms.

Africa↗