Raymond Noblet

Biological Transmission of Vesicular Stomatitis Virus (New Jersey Serotype) by Simulium vittatum (Diptera: Simuliidae) to Domestic Swine (Sus scrofa)

Abstract The role of hematophagous arthropods in vesicular stomatitis virus (New Jersey serotype; VSV-NJ) transmission during epizootics has remained unclear for decades in part because it has never been shown that clinical or subclinical disease in a livestock host results from the bite of an infected insect. In this study, we investigated the ability of VSV-NJ–infected black flies (Simulium vittatum Zetterstedt) to transmit the virus to domestic swine, Sus scrofa L. Experimental evidence presented here clearly demonstrates that VSV-NJ was transmitted from black flies to the swine. Transmission was confirmed by seroconversion or by the presence of clinical vesicular stomatitis followed by seroconversion. Our results represent the first report of clinical vesicular stomatitis in a livestock host after virus transmission by an insect.

Experimental Transmission of Vesicular Stomatitis New Jersey Virus from Simulium vittatum to Cattle: Clinical Outcome is Influenced by Site of Insect Feeding

ABSTRACT 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.

Mechanical Transmission of Vesicular Stomatitis New Jersey Virus by Simulium vittatum (Diptera: Simuliidae) to Domestic Swine (Sus scrofa)

ABSTRACT Biting flies have been suggested as mechanical vectors of vesicular stomatitis New Jersey Virus (family Rhabdoviridae, genus Vesiculovirus, VSNJV) in livestock populations during epidemic outbreaks in the western United States. We conducted a proof-of-concept study to determine whether biting flies could mechanically transmit VSNJV to livestock by using a black fly, Simulium vittatum Zetterstedt (Diptera: Simuliidae), domestic swine, Sus scrofa L., model. Black flies mechanically transmitted VSNJV to a naïve host after interrupted feeding on a vesicular lesion on a previously infected host. Transmission resulted in clinical disease in the naïve host. This is the first demonstration of mechanical transmission of VSNJV to livestock by insects.

Plasmodium gallinaceum: effects of various compounds on immunity of susceptible Aedes aegypti and refractory Culex pipiens pipiens.

Abstract Para-aminobenzoic acid (PABA) administered in the diet in 0.01, 0.1, 0.2, 0.3, 0.4, and 1.0% concentrations to Aedes aegypti was found to enhance oocyst production. The most significant increase in oocyst production was in groups receiving 0.3 and 0.1% solutions. A combination of 0.01% PABA + 0.1 M NaOH, and 0.02 M HCL, 0.1 M KOH, 0.1 M NaOH, and 0.2 M MgCl2 likewise increased the susceptibility of A. aegypti to Plasmodium gallinaceum with 0.1 M NaOH being the most effective. Culex pipiens pipiens was found to exhibit a low degree of susceptibility to P. gallinaceum. This is the first report of oocyst development by P. gallinaceum in this species. PABA in 0.1, 0.2, 0.3, 0.4, and 1.0% concentrations was tested and all concentrations increased the susceptibility of this refractory host. This compound was most effective in a 0.4% concentration. The susceptibility of C. pipiens pipiens to P. gallinaceum was also increased by inorganic materials. NaOH and KOH in 0.1 M concentrations yielded the greatest increase. A slight increase in susceptibility was effected by 0.2 M MgCl2 and 0.02 M HCL. Culex receiving the combination of 0.01% PABA and 0.01 M NaOH had the highest infection of those receiving inorganic compounds. Most of the oocysts produced in these experimental Culex were fairly typical of those found in A. aegypti; however, some were quite small and others showed evidence of deterioration, distortion, and shrinkage.

Plasmodium gallinaceum: Development in Aedes aegypti maintained on various carbohydrate diets☆

Abstract Fructose, galactose, glucose, maltose, melibiose, and trehalose were evaluated for their nutritional and survival values for Aedes aegypti. The development of the exogenous stages of Plasmodium gallinaceum was evaluated by counting and averaging the number of oocysts developing on the midguts of Aedes aegypti. The nutritional and survival value for A. aegypti was greatest on glucose, sucrose, and fructose and lowest on galactose and melibiose. Mosquitoes maintained on fructose produced the greatest numbers of oocysts. Only two other sugars, galactose and melibiose produced more oocysts than their respective controls. Glucose and maltose, both of which had high nutritive and survival value for A. aegypti were less efficient than the control (sucrose) for the development of P. gallinaceum.

Identification of Human Semiochemicals Attractive to the Major Vectors of Onchocerciasis

Background Entomological indicators are considered key metrics to document the interruption of transmission of Onchocerca volvulus, the etiological agent of human onchocerciasis. Human landing collection is the standard employed for collection of the vectors for this parasite. Recent studies reported the development of traps that have the potential for replacing humans for surveillance of O. volvulus in the vector population. However, the key chemical components of human odor that are attractive to vector black flies have not been identified. Methodology/Principal Findings Human sweat compounds were analyzed using GC-MS analysis and compounds common to three individuals identified. These common compounds, with others previously identified as attractive to other hematophagous arthropods were evaluated for their ability to stimulate and attract the major onchocerciasis vectors in Africa (Simulium damnosum sensu lato) and Latin America (Simulium ochraceum s. l.) using electroantennography and a Y tube binary choice assay. Medium chain length carboxylic acids and aldehydes were neurostimulatory for S. damnosum s.l. while S. ochraceum s.l. was stimulated by short chain aliphatic alcohols and aldehydes. Both species were attracted to ammonium bicarbonate and acetophenone. The compounds were shown to be attractive to the relevant vector species in field studies, when incorporated into a formulation that permitted a continuous release of the compound over time and used in concert with previously developed trap platforms. Conclusions/Significance The identification of compounds attractive to the major vectors of O. volvulus will permit the development of optimized traps. Such traps may replace the use of human vector collectors for monitoring the effectiveness of onchocerciasis elimination programs and could find use as a contributing component in an integrated vector control/drug program aimed at eliminating river blindness in Africa.

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.

The Effect of Seston on Mortality of Simulium vittatum (Diptera: Simuliidae) from Insecticidal Proteins Produced by Bacillus thuringiensis subsp. israelensis

ABSTRACT Water was collected from a site on the Susquehanna River in eastern Pennsylvania, where less-than-optimal black fly larval mortality had been occasionally observed after treatment with Bacillus thuringiensis subsp. israelensis de Barjac insecticidal crystalline proteins (Bti ICPs). A series of experiments was conducted with Simulium vittatum Zetterstedt larvae to determine the water related factors responsible for the impaired response to Bti ICPs (Vectobac 12S, strain AM 65–52). Seston in the water impaired the effectiveness of the ICPs, whereas the dissolved substances had no impact on larval mortality. Individual components of the seston then were exposed to the larvae followed by exposure to Bti ICPs. Exposure of larvae to selected minerals and nutritive organic material before ICP exposure resulted in no significant decrease in mortality. Exposure of larvae to silicon dioxide, cellulose, viable diatoms, and purified diatom frustules before Bti ICP exposure resulted in significant reductions in mortality. Exposure of larvae to purified diatom frustules from Cyclotella meneghiniana Kützing resulted in the most severe impairment of mortality after Bti ICP exposure. It is postulated that frustule-induced impairment of feeding behavior is responsible for the impairment of larval mortality.

Host predilection and transmissibility of vesicular stomatitis New Jersey virus strains in domestic cattle ( Bos taurus ) and swine ( Sus scrofa )

BackgroundEpidemiologic data collected during epidemics in the western United States combined with limited experimental studies involving swine and cattle suggest that host predilection of epidemic vesicular stomatitis New Jersey virus (VSNJV) strains results in variations in clinical response, extent and duration of virus shedding and transmissibility following infection in different hosts. Laboratory challenge of livestock with heterologous VSNJV strains to investigate potential viral predilections for these hosts has not been thoroughly investigated. In separate trials, homologous VSNJV strains (NJ82COB and NJ82AZB), and heterologous strains (NJ06WYE and NJOSF [Ossabaw Island, sand fly]) were inoculated into cattle via infected black fly bite. NJ82AZB and NJ06WYE were similarly inoculated into swine.ResultsClinical scores among viruses infecting cattle were significantly different and indicated that infection with a homologous virus resulted in more severe clinical presentation and greater extent and duration of viral shedding. No differences in clinical severity or extent and duration of viral shedding were detected in swine.ConclusionsDifferences in clinical presentation and extent and duration of viral shedding may have direct impacts on viral spread during epidemics. Viral transmission via animal-to-animal contact and insect vectored transmission are likely to occur at higher rates when affected animals are presenting severe clinical signs and shedding high concentrations of virus. More virulent viral strains resulting in more severe disease in livestock hosts are expected to spread more rapidly and greater distances during epidemics than those causing mild or inapparent signs.

INFLUENCE OF SELECTED ANTIBIOTICS ON THE RESPONSE OF BLACK FLY (SIMULIUM VITTATUM) LARVAE TO INSECTICIDAL PROTEINS PRODUCED BY BACILLUS THURINGIENSIS SUBSP. ISRAELENSIS

A controlled current toxicity test (CCTT) was developed to evaluate the response of black fly (Simulium vittatum) larvae to insecticidal proteins following exposure to various antibiotics. The bacterium, Bacillus thuringiensis subsp. israelensis (Bti), produces proteins that are toxic to Nemotoceran Diptera, such as black flies and mosquitoes, when ingested. These insecticidal crystalline proteins (ICPs) are highly efficacious in controlling black flies; however, speculation has arisen regarding the potential for antibiotic contamination of waterways to mitigate the toxicity of these proteins. A series of experiments was conducted with the CCTT in which black fly larvae were exposed to enrofloxacin, tylosin, sulfamethoxazole, and trimethoprim followed by exposure to Bti ICPs. These antibiotics were selected based on their use in agricultural and documented anthropogenic contamination of rivers. Anthropogenic concentrations of a mixture of these four antibiotics did not affect the response of the larvae to Bti ICPs. Subsequent experiments were conducted with antibiotic concentrations 10,000 to 80,000 times higher than those found in contaminated rivers. Exposure of black fly larvae to high levels of enrofloxacin (0.5 mg/L) had no effect upon the susceptibility to Bti ICPs; however, exposure to high levels of tylosin (8 mg/L) resulted in a significant increase in the susceptibility of the larvae to Bti ICPs at 72 h of exposure, but not at 48 h. Exposure of black fly larvae to high concentrations of a mixture of sulfamethoxazole and trimethoprim resulted in a significant increase in the efficacy of the larvicide after 48 and 72 h of exposure. These results suggest that impairment of the efficacy of Bti ICPs to black fly larvae is not due to antibiotic contamination of the larval environment.