There is no credible evidence that the lentivirus that causes equine infectious anaemia (EIA) replicates in invertebrates. The virus persistently infects its equid hosts and is often present in blood ...in significant quantities. Blood-feeding arthropods thus have the potential to transfer the virus between hosts, especially if their feeding on the first host is interrupted and immediately continued on a second host. The general details and dynamics of mechanical transmission are included in this paper, as this agent presents an excellent model. Mechanical transmission can be effectively controlled if the dynamics and interactions of the host, virus and vector populations are understood. Efficient transmission is proportional to the amount of agent found in the source material, the environmental survival of the agent, the number of vector feedings, the number of interrupted feedings, vector refeeding, the proximity of infected and naive hosts, host population density, and the length of time during which vectors and hosts are in contact. Establishing firm quantitative risk estimates for EIA is impossible, mainly because the virus content in blood can change exponentially from day to day. The EIA virus can be transmitted by horse flies for at least 30 minutes after feeding on a horse with acute signs of EIA, butthe probability of a horse fly being interrupted and completing its blood feeding on a second host at a distance of 50 m is very low, and the separation of infected and uninfected equids by 200 m breaks transmission. The statements above assume that human interactions are absent or do not contribute to the risk of virus transmission; however, the risk from human interventions, such as the too-often-used procedure of administering > 200 ml of plasma to foals, can easily be more than 10(7) times greater than the risk posed by a single horse fly. Controlling EIA depends upon the identification of persistently infected equids by serological testing because other methods of identifying infective virus orviral genetic material are less accurate or impractical.
Pesticides are used worldwide to control arthropod parasites in cattle herds. The indiscriminate and/or inappropriate use of pesticides without veterinary guidance is a reality in several countries ...of South America. Improper pesticide use increases the chances of contamination of food and the environment with chemical pesticides and their metabolites. Reduction of these contamination events is an increasing challenge for those involved in livestock production. The horn fly, Haematobia irritans (Linnaeus) (Diptera: Muscidae), is one of the most economically important parasites affecting cattle herds around the world. As such, horn fly control efforts are often required to promote the best productive performance of herds. Pesticide susceptibility bioassays revealed that pyrethroid resistance was widespread and reached high levels in horn fly populations in the Brazilian state of Rondônia. The knockdown resistance (kdr) sodium channel gene mutation was detected in all horn fly populations studied (n = 48), and the super kdr sodium channel gene mutation was found in all homozygous resistant kdr individuals (n = 204). Organophosphate resistance was not identified in any of the fly populations evaluated.
The horn fly is one of the most economically important parasites affecting cattle herds around the world.
Pesticide control in horn fly populations promotes excellent initial results, but the excessive use of these compounds results in insecticide resistance issues.
The selection pressure imposed by pesticides means that as pesticide effectiveness increases, so do the selection for and rapidity of resistance development in horn fly populations.
In horn flies, Haematobia irritans irritans (Diptera: Muscidae) (Linnaeus, 1758), target site resistance to pyrethroids can be diagnosed by an allele‐specific PCR that genotypes individual flies at ...both the super‐kdr (skdr) and the knock down resistance (kdr) associated loci. When this technique uses genomic DNA as template, modifications, such as alternative RNA splicing and RNA editing are not specifically detected. Alternative splicing at the skdr locus has been reported in Dipterans; thus, the genomic DNA‐based allele‐specific PCR may not accurately reflect the frequency of the skdr mutation in horn fly field populations. To investigate if alternative splicing occurs at the skdr locus of horn flies, genomic DNA and cDNA sequences isolated from two wild populations and two laboratory‐reared colonies with varying degrees of pyrethroid resistance were compared. There was no indication of alternative splicing at the super‐kdr locus neither in the wild populations nor in the laboratory‐reared colonies.
All cDNA clones had the same nucleotide sequence, differing only at the super‐kdr locus. The cDNA and genomic sequences were identical matches, except for a variable intron in the genomic sequences.
Unlike what has been reported for other Dipterans, only exon d of the sodium channel was found in the studied horn fly populations.
There was no indication of alternative splicing at the super‐kdr locus, neither in the wild populations nor in the laboratory‐reared colonies.
The sand fly Phlebotomus papatasi Scopoli is the vector of Leishmania major (Yakimoff & Schokhor), which is maintained in populations of burrowing rodents. The purpose of this study was to conduct a ...laboratory study to determine the efficacy of oral treatment of rodents with fipronil for control of sand flies that feed on rodent feces as larvae or on rodent blood as adults. We determined through larval bioassays that fipronil was eliminated in feces of orally-treated hamsters at a level that was significantly toxic to sand fly larvae for 21 d after the hamsters had been withdrawn from a fipronil-treated diet. Through bloodfeeding bioassays, we also found that fipronil was present in the peripheral blood of hamsters at a concentration that was significantly toxic to bloodfeeding adult female sand flies for 49 d after the hamsters had been withdrawn from their treated diet. The results of this study suggest that fipronil acts as well as or better than feed-through or systemic insecticides that previously have been measured against sand flies, and is particularly promising because this single compound acts against both larvae and bloodfeeding adults. An area-wide approach using rodent baits containing a fipronil could suppress vector populations that originate in the vicinity of rodent reservoirs, and could be used to eliminate the most epidemiologically important part of the vector population: female sand flies that take bloodmeals on rodent reservoirs.
The macrocyclic lactone ivermectin was evaluated as a rodent systemic and feed-through insecticide for control of adult and immature sand flies (
Phlebotomus papatasi Scopoli). Syrian hamsters were ...fed diets containing 0 or 20
mg/kg ivermectin for 9 days, and sand flies were allowed to take bloodmeals from the hamsters 0, 3, 7, and 14 days after they were withdrawn from their diets. Ivermectin treatment of hamsters was 100% effective against bloodfeeding sand flies for up to 7 days after hamsters were withdrawn from ivermectin-treated diets. The survival and fecundity of sand flies that took bloodmeals from hamsters 14 days after they had been withdrawn from their ivermectin-treated diets were not significantly different from sand flies that took bloodmeals from control hamsters. Feces of the hamsters were collected 0, 3, 7, and 14 days after the hamsters had been withdrawn from their diets, and the feces were fed to 2nd instars of
P. papatasi. All larvae that were fed feces of ivermectin-treated hamsters voided 0 days after being withdrawn from their diets died before pupation; larvae fed feces voided by ivermectin-treated hamsters 3 and 7 days after being withdrawn from their treated diets had significantly reduced survival. The results of this study suggest that oral ivermectin treatment of rodents could control immature and adult female sand flies that are closely associated with rodents.
Two studies evaluated the potential use of spatial barriers to reduce the mechanical transmission of disease agents by tabanids in the Pantanal region of Brazil. Tabanids at stations separated by ...four different distances (5, 10, 25, and 50
m) were marked. In the first study, tabanids were marked and allowed to feed until engorgement or natural interruption occurred and captured if they transferred to the other horse. A total of 2847 tabanids belonging to nine different species were marked. The percentage of tabanids that moved between horses was 10.5 at 5
m, 6.8 at 10
m, and 4.6 at 25
m. In the second study, flies were marked, feeding was then interrupted, and the flies were released approximately 50
cm from the host. A total of 1274 tabanids belonging to five different species were marked. The percentage of flies that moved between horses was 9.7 at 5
m, 9.7 at 10
m, and 4.6 at 25
m. No tabanids transferred between animals separated by 50
m in either experiment. The results of this study strongly support the recommendation that segregation of animals effectively prevents the mechanical transmission of pathogens by tabanids.
The performance of Nzi traps for tabanids (Tabanus similis Macquart, T. quinquevittatus Wiedemann, Chrysops aberrans Philip, C. univittatus Macquart, C. cincticornis Walker, Hybomitra lasiophthalma ...(Macquart)), stable flies (Stomoxys calcitrans Linnaeus) (Diptera: Muscidae) and mosquitoes (Aedes) (Diptera: Culicidae) was investigated at various sites in Canada (Ontario, Alberta) and USA (Iowa, Florida, Louisiana). Traps made from selected fabrics, insect nettings and hand-dyed blue cotton were compared to the African design to provide practical recommendations for temperate environments. Comparisons of substituted materials showed that trap performance was optimal only when traps were made from appropriate fabrics in the colours produced by either copper phthalocyanine (phthalogen blue), or its sulphonated forms (turquoise). Fabrics dyed with other blue chromophores were not as effective (anthraquinone, disazo, formazan, indanthrone, triphenodioxazine). An appropriate texture as well as an appropriate colour was critical for optimal performance. Smooth, shiny synthetic fabrics (polyester, nylon) and polyester blends reduced catches. Low catches occurred even for nominal phthalogen blue, but slightly-shiny, polyester fabrics in widespread use for tsetse. The most suitable retail fabric in place of phthalogen blue cotton was Sunbrella Pacific Blue acrylic awning/marine fabric. It was both attractive and durable, and had a matching colour-fast black. Nzi traps caught grossly similar numbers of biting flies as canopy, Vavoua, and Alsynite cylinder traps, but with differences in relative performance among species or locations.
The purpose of this study was to evaluate the use of four fluorescent dyes (rhodamine B, uranine O, auramine O, and erythrosin B) and two nonfluorescent dyes (carmoisine and indigotine) incorporated ...into sugar baits as biomarkers for phlebotomine sand flies, Each dye could be detected in sand flies fed baits with dye for 24 h when examined using bright field microscopy, although there was considerable variability in the marking produced; all sand flies that had ingested rhodamine B-treated sucrose solution were marked clearly. Sand flies that had ingested sucrose solution containing rhodamine B or uranine O at concentrations as low as 10 mg/L were consistently detected under fluorescence microscopy. None of the treatments in this study reduced the longevity of sand flies. All sand flies fed sucrose solution containing rhodamine B or uranine O were marked for at least 14 d, whereas only 20% of sand flies were marked 3 d after feeding on a carmoisine-treated solution. When rhodamine B and uranine O were combined in a single sucrose solution or when the dyes were fed sequentially to sand flies, both dyes could be detected in sand flies using fluorescence microscopy. We propose that rhodamine B- or uranine O-treated sucrose baits could be used in ecological studies or to identify portions of the adult sand fly population that could be targeted with insecticide-treated sugar baits.
The purpose of this study was to evaluate the use of rhodamine B as an orally delivered biomarker for rodents and a feed-through transtadial biomarker for phlebotomine sand flies (Diptera: ...Psychodidae ). Rhodamine B-treated hamsters were visibly marked for up to 8 wk, and their feces were fluorescent when examined under a fluorescence microscope. The development and survival of sand fly larvae fed feces of rhodamine B-treated hamsters were not significantly different from control sand flies. Adult male and female sand flies, that had been fed as larvae the feces of rhodamine B-treated hamsters, were fluorescent when examined using fluorescent microscopy and could be distinguished from control sand flies. Adult female sand flies that took bloodmeals from rhodamine B-treated hamsters were fluorescent when examined immediately after feeding. Rhodamine B incorporated rodent baits could be used to detect adult male and female sand flies that fed on the feces of baited rodents as larvae, or adult female sand flies that have taken a bloodmeal from bait-fed rodents. This would allow the delineation of specific foci with rodent-sand fly associations that would be susceptible to control by using feed-through or systemic insecticides.
The efficacy of 3 rodent feed-through insecticides (novaluron, pyriproxyfen, and ivermectin) was determined against larvae of the sand flies Phlebotomus duboscqi and P. papatasi using Syrian hamsters ...(Mesocricetus auratus) and Mongolian gerbils (Meriones unguiculatus) as laboratory models. For each insecticide, there were no significant differences between the longevity or percentage survival of sand fly larvae that had been fed feces of treated rodents for each sand fly or rodent species pairing. The results of this study suggest that larvae of P. duboscqi and P. papatasi are equally susceptible to the concentrations of the rodent feed-through insecticides tested in this study and that these insecticides are pharmacologically compatible with different rodent/sand fly interactions.
PDF
