Pathogenesis of Vesicular Stomatitis New Jersey Virus Infection in Deer Mice ( Peromyscus maniculatus) Transmitted by Black Flies ( Simulium vittatum).

The natural transmission of vesicular stomatitis New Jersey virus (VSNJV), an arthropod-borne virus, is not completely understood. Rodents may have a role as reservoir or amplifying hosts. In this study, juvenile and nestling deer mice ( Peromyscus maniculatus) were exposed to VSNJV-infected black fly ( Simulium vittatum) bites followed by a second exposure to naive black flies on the nestling mice. Severe neurological signs were observed in some juvenile mice by 6 to 8 days postinoculation (DPI); viremia was not detected in 25 juvenile deer mice following exposure to VSNJV-infected fly bites. Both juvenile and nestling mice had lesions and viral antigen in the central nervous system (CNS); in juveniles, their distribution suggested that the sensory pathway was the most likely route to the CNS. In contrast, a hematogenous route was probably involved in nestling mice, since all of these mice developed viremia and had widespread antigen distribution in the CNS and other tissues on 2 DPI. VSNJV was recovered from naive flies that fed on viremic nestling mice. This is the first report of viremia in a potential natural host following infection with VSNJV via insect bite and conversely of an insect becoming infected with VSNJV by feeding on a viremic host. These results, along with histopathology and immunohistochemistry, show that nestling mice have widespread dissemination of VSNJV following VSNJV-infected black fly bite and are a potential reservoir or amplifying host for VSNJV.

Identification of semiochemicals attractive to Simulium vittatum (IS-7).

Many blackfly species (Diptera: Simuliidae) are economically important insect pests, both as nuisance biters and as vectors of pathogens of medical and veterinary relevance. Among the important blackfly pest species in North America is Simulium vittatum Zetterstedt sensu lato. The objective of this study was to identify compounds excreted by mammalian hosts that are attractive to host-seeking S. vittatum females. The attractiveness of putative compounds to colonized S. vittatum was tested through electrophysiological (electroantennography; n = 58 compounds) and behavioural (Y-tube assays; n = 7 compounds in three concentrations) bioassays. Five compounds were significantly attractive to host-seeking S. vittatum females: 1-octen-3-ol; 2-heptanone; acetophenone; 1-octanol, and naphthalene. These candidate compounds might be useful as attractants in traps that could be developed for use in alternative or complementary management tactics in programmes to suppress nuisance blackfly populations, or for the collection of samples in which to study the transmission ecology of pathogens transmitted by blackflies of the S. vittatum complex.

Domestic cattle as a non-conventional amplifying host of vesicular stomatitis New Jersey virus.

The role of vertebrates as amplifying and maintenance hosts for vesicular stomatitis New Jersey virus (VSNJV) remains unclear. Livestock have been considered dead-end hosts because detectable viraemia is absent in VSNJV-infected animals. This study demonstrated two situations in which cattle can represent a source of VSNJV to Simulium vittatum Zetterstedt (Diptera: Simuliidae) by serving: (a) as a substrate for horizontal transmission among co-feeding black flies, and (b) as a source of infection to uninfected black flies feeding on sites where VSNJV-infected black flies have previously fed. Observed co-feeding transmission rates ranged from 0% to 67%. Uninfected flies physically separated from infected flies by a distance of up to 11 cm were able to acquire virus during feeding although the rate of transmission decreased as the distance between infected and uninfected flies increased. Acquisition of VSNJV by uninfected flies feeding on initial inoculation sites at 24 h, 48 h and 72 h post-infection, in both the presence and absence of vesicular lesions, was detected.

Experimental transmission of vesicular stomatitis New Jersey virus from Simulium vittatum to cattle: clinical outcome is influenced by site of insect feeding.

Vesicular stomatitis New Jersey virus (VSNJV) is an insect-transmitted Rhabdovirus causing vesicular disease in domestic livestock including cattle, horses, and pigs. Natural transmission during epidemics remains poorly understood, particularly in cattle, one of the most affected species during outbreaks. This study reports the first successful transmission of VSNJV to cattle by insect bite resulting in clinical disease. When infected black flies (Simulium vittatum Zetterstedt) fed at sites where VS lesions are usually observed (mouth, nostrils, and foot coronary band), infection occurred, characterized by local viral replication, vesicular lesions, and high neutralizing antibody titers (> 1: 256). Viral RNA was detected up to 9 d postinfection in tissues collected during necropsy from lesion sites and lymph nodes draining those sites. Interestingly, when flies were allowed to feed on flank or neck skin, viral replication was poor, lesions were not observed, and low levels of neutralizing antibodies (range, 1:8-1:32) developed. Viremia was never observed in any of the animals and infectious virus was not recovered from tissues on necropsies performed between 8 and 27 d postinfection. Demonstration that VSNJV transmission to cattle by infected black flies can result in clinical disease contributes to a better understanding of the epidemiology and potential prevention and control methods for this important disease.

Influences of a laboratory diet and natural seston on the bioavailability of carbaryl, chlorpyrifos, and malathion to black fly larvae (Diptera: Simuliidae) in an acute toxicity test.

To determine the effects organic food particles can have on insecticide bioavailability, two food types, a laboratory diet and dried, natural seston, were evaluated using black fly larvae, Simulium virtatum Zetterstedt cytospecies IS-7, in a 24-h orbital shaker toxicity test. The bioavailability of all three insecticides was significantly altered when diet concentrations in the flasks were > or = 150 mg/L. Chlorpyrifos availability decreased, whereas carbaryl and malathion availability increased. Dried, natural seston had little effect on the bioavailability of these insecticides except in carbaryl-dosed larvae where mortality was significantly increased when seston concentrations were 150 mg/L in the flasks. Differences in insecticide bioavailability between the two food types in these experiments might have been related to the particle size and organic carbon content of the two materials. Laboratory diet particles were significantly smaller (11.7 +/- 0.5 microm) and had a significantly greater organic carbon content (26.4%) than the seston particles (30.9 +/- 3.3 microm; 1.1%). These results suggest that the concentration, as well as the physical and chemical component of the food source, are important factors in determining the effects of food on insecticide bioavailability in aquatic systems.

Development of the first black fly (Diptera: Simuliidae) management program in Argentina and comparison with other programs.

In response to increasing pest populations of black flies, the government of Argentina initiated a pilot program to evaluate the effectiveness of larval control in the irrigation system of the Negro River Valley, an 18,240-km2 area in Patagonia. The extensive system of irrigation canals, drainage ditches, and natural waterways not only provides water for agriculture and general habitation but also affords habitat for immature black flies. Three species (Simulium bonaerense, Simulium wolffhuegeli, and Simulium nigristrigatum) are primary pests of humans and animals in this area. Trials were conducted using Vectobac AS in representative irrigation canals, a drainage ditch, and a medium-sized river. Most trials resulted in effective larval mortality and insecticide carry. Based on a comparison with 11 black fly suppression programs throughout the world, a suppression program for the Negro River Valley has a projected cost of approximately $1,623,360/year. This study represents the initial steps in development of the 1st areawide black fly suppression program in Argentina.

Economic impact of black flies (Diptera:Simuliidae) in South Carolina and development of a localized suppression program.

The membership of a private golf club in South Carolina's Piedmont Physiographic Region was surveyed to determine perceptions regarding local black fly populations and the effects of these populations on golfing habits. The economic impact of black fly annoyance at this club was estimated to be $27,202. Adult monitoring indicated that the pest species were members of the Simulium jenningsi group; larval monitoring identified the Enoree River, Laurens County, as the primary source of the pest species. A localized suppression program was initiated during the late summer of 1994 and continued through the fall of 1995. Four larvicide applications were conducted in 1994 and 11 in 1995, using the biological insecticide Vectobac. Larval mortalities of 94.5 and 97% were produced during 1994 and 1995, respectively. Adult black fly populations were reduced 92 and 88% during 1994 and 1995, respectively, from pre-program populations. Improvements for future suppression programs are proposed.

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.

A simple technique for determining relative toxicities of Bacillus thuringiensis var. Israelensis formulations against larval blackflies (Diptera: Simuliidae).

A laboratory system for assaying the potency of Bacillus thuringiensis var. israelensis formulations against larval blackflies was developed. An orbital shaker was used to create a water current in 250-ml Erlenmeyer flasks containing the test larvae. This system produced dose-mortality relationships with acceptable statistical parameters.

The Morgan Recharger: a new horn fly (Diptera: Muscidae) control device for beef cattle.

A 20% diazinon formulation was evaluated for control efficacy against the horn fly, Haematobia irritans (L.), in the Morgan Recharger (Morgan International Products, College Grove, Tenn.). The Morgan Recharger releases insecticide with a wicking system from an insecticide reservoir and can be attached to an animal's ear or tail. This device was most effective against the horn fly when used as an ear tag with two per head; horn fly counts did not exceed five flies per side through 8 wk. The diazinon formulation tested was released from the Morgan Recharger at a decreasing rate. The problems and potential of the Morgan Recharger as an effective horn fly control device are discussed.

Effects of feeding schedules on diurnal periodicity of Leucocytozoon smithi gametocytes in the peripheral blood of domestic turkeys.

Eighteen domestic turkeys naturally infected with Leucocytozoon smithi Laveran & Lucet were maintained on restricted feeding schedules under conditions of either continuous light or natural light (light 13 h:darkness 11 h) photoperiods. Peripheral gametocyte numbers of L. smithi in all turkeys were determined every 2 h over a 36-h period. Peripheral gametocyte numbers of turkeys maintained under continuous light and restricted to either a 10-h feeding period (9:30 p.m. to 7:30 a.m.) once a day or a 2-h feeding period twice a day (7:30 a.m. to 9:30 p.m. and 7:30 p.m. to 9:30 p.m.) increased at or near the time of feed availability. Under natural photoperiod, gametocyte periodicity was not affected by restricting feed availability to the dark phase of the light-dark cycle. Mean parasite numbers were highest during the light phase when feed was not available, and lowest during the dark period when feed was accessible.

Toxicological studies with mirex in bobwhite quail.

Bobwhite quail (Colinus virginianus) received dietary mirex in concentrations of 1, 20 and 40 ppm to investigate reproductive effects of long term exposure to this chemical. Residue analyses of Fo generation breeders indicated that male adipose tissue contained approximately 10 times the mirex level in the diet. Elimination of mirex in females probably was facilitated by egg laying, which reduced mirex buildup in adipose tissue to five times the dietary level. Both sexes were noted to concentrate mirex in fat and breast tissue in direct proportion to the intake of dietary mirex. Eggs collected from Fo generation breeders were not affected deleteriously by mirex as measured by embryo survival to 3 weeks, and thenumber of eggs failing to hatch. Indeed, increased rates of egg fertility and hatchability were associated with higher dietary concentrations. Chick survival data was obtained in Fp and F1 generation hatchlings from hatching through 2 weeks. No chick mortality attributable to pesticide stress was detected in either group of birds. Eggs collected from F1 generation breeders that received 1 ppm were not affected harmfully as measured by embryonation, embryo survival, and hatchability rates. Comparison of residues in wild bobwhites with residues in our experimental findings indicates mirex is apparently not affecting deleteriously reproductive success of wild quail.

Mirex residues in bobwhite quail after aerial application of bait for fire ant control, South Carolina--1975-76.

Mirex, the organochlorine compound used for control of the imported fire ant (Solenopsis invicta Buren), was applied aerially under supervision of the South Carolina Plant Pest Regulatory Service in October 1975 to a game management area in Hampton County, S.C. Influenced by recent reports indicating that low levels of mirex were toxic to certain nontarget organisms in laboratory studies, authors initiated a program for monitoring mirex residues in bobwhite quail (Colinus virginianus). Pretreatment residues were recorded on a dry-weight basis in bobwhite quail breast and adipose tissue; conversion factors for determining wet-weight concentrations are approximately as follows: fat, 0.77; and breast, 0.29. Residues ranged from 0.000-0.178 ppm and 0.247-2.763 ppm, respectively. Mirex residues in quail adipose tissue showed up to five-fold increase within the first month after treatment and declined thereafter. A residue peak was noticed the spring following mirex treatment, corresponding with insect emergence. Mirex residues in quail collected in summer 1976 following a fall bait application showed slightly higher residue levels than had birds taken in summer 1975; however, little, if any, human food chain contamination would result in the consumption of birds with residue levels found in this study.

Effect of photoperiod on the diurnal periodicity of Leucocytozoon smithi gametocytes in the peripheral blood of domestic turkeys.

The daily cyclical variation in Leucocytozoon smithi gametocyte numbers in the peripheral blood of domestic turkeys was shifted 12-hr. by exposure of hosts to a reversed photoperiod. Peak parasitemia coincided with the midpoint of the artificial light period (0100 hr.), while low parasitemia occurred between 1300 hr. and 1700 hr. Disruption of strict gametocyte periodicity was suggested by results of birds exposed to light varying in intensity from 700 lux during the day to 161 lux at night although marked fluctuations in gametocyte numbers occurred.

Periodicity of Leucocytozoon smithi gametocytes in the peripheral blood of domestic turkeys.

Gametocytes of Leucocytozoon smithi exhibited a cyclic activity both in cardiac and peripheral blood of domestic turkeys during a given 24-hr. period. Peak parasitemias occurred from 0800 to 2000 hr., and mean low parasitemias from 2200 to 0400. The most prominent feeding period of the vector Simulium slossonae coincided with the period of elevated parasitemia in the turkey host.

Survey of leucocytozoon in in South Carolina.

An extensive survey of birds for Leucocytozoon in South Carolina during the summer of 1972 revealed that Blue Jays, Purple Grackles and domestic chickens were commonly infected. No alternate hosts were found for Leucocytozoon smithi of turkeys.