Oral transmission of Jamestown Canyon virus by Aedes provocans mosquitoes from northeastern New York.

Aedes provocans were allowed to feed on a bloodmeal containing 5.6 log10 TCID50/ml of Jamestown Canyon (JC) virus. After 14 days of incubation at 21 degrees C and 80% RH, 100% (36/36) were midgut infected, 50% (18/36) developed disseminated infections and 50% (9/18) of the latter specimens transmitted virus to capillary tubes. When mosquitoes were intrathoracically inoculated with 6.1 log10 TCID50/ml of JC virus, 100% (40/40) became disseminated infected and 95% (38/40) transmitted virus after 12 days of incubation. A midgut escape barrier was recognized as the major barrier to JC virus transmission in orally infected Ae. provocans.     

Effects of time after infection, mosquito genotype, and infectious viral dose on the dynamics of Culex tarsalis vector competence for western equine encephalomyelitis virus

The vector competence of Culex tarsalis Coquillett for the BFS 1703 strain of western equine encephalomyelitis virus (WEEV) changed significantly as a function of time after infection, mosquito genotype, and infectious virus dose. After ingesting a high virus dose (5 log10 plaque-forming units [PFU]/0.1 ml), female of the susceptible high virus producer (HVP) strain rapidly amplified the virus, developed a disseminated infection, and efficiently transmitted WEEV by 4 days postinfection (dpi). The quantity of virus expectorated peaked at 4 dpi (mean 3.4 log10 PFU), and the percentage of females transmitting per os peaked at 7 dpi (80%); both measures of transmission subsequently decreased to low levels throughout the remainder of infected life. HVP females imbibing a low virus dose (3 log10 PFU/0.1 ml) were infected less frequently and took longer to amplify virus to levels recorded for the high virus dose group and did not transmit virus efficiently, thereby indicating midgut infection and escape barriers were dose and time dependent. These data emphasized the importance of elevated avian viremias in Cx. tarsalis vector competence. Females from the WEEV-resistant (WR) strain and two wild-type strains from Kern and Riverside counties were significantly less susceptible to infection at both high and low doses than was the HVP strain. Overall, females with a high virus titer more frequently had a disseminated infection, but there did not seem to be a distinct threshold demarcating this relationship. In marked contrast, all infected females transmitting virus had body titers >4.3 log10 PFU, and most had titers >4.8 log10 PFU. These data indicated that not all females with a disseminated infection transmitted virus because of the presence of one or more salivary gland barriers.     

Vector competence of Kenyan Culex zombaensis and Culex quinquefasciatus mosquitoes for Rift Valley fever virus

Rift Valley fever (RVF) continues to be a significant problem in Kenya as well as in Egypt, Yemen, and Saudi Arabia. In order to determine the ability of Kenyan mosquitoes to transmit RVF virus (RVFV), we collected mosquitoes in the Lake Naivasha region of Kenya and evaluated them for their potential to transmit RVFV under laboratory conditions. After feeding on a hamster (Mesocricetus auratus) with a viremia of 10(9.7) plaque-forming units of virus/ml of blood, Culex zombaensis were highly susceptible to infection with RVFV, with 89% becoming infected. In contrast, Cx. quinquefasciatus that were fed on the same hamsters were marginally susceptible, with only 20% becoming infected. Differences in percentages of mosquitoes that developed a disseminated infection were equally disparate, with 55% and 8%, for Cx. zombaensis and Cx. quinquefasciatus, respectively. Forty-eight percent of the Cx. zombaensis with a disseminated infection that fed on a susceptible hamster transmitted virus by bite, indicating a moderate salivary gland barrier. However, the presence of a salivary gland barrier could not be determined for Cx. quinquefasciatus because none of the 18 mosquitoes that took a 2nd blood meal had a disseminated infection. These studies illustrate the need to identify the ability of individual mosquito species to transmit RVFV so that correct decisions can be made concerning the application of appropriate control measures during an outbreak.     

Experimental infection of horses with West Nile virus

A total of 12 horses of different breeds and ages were infected with West Nile virus (WNV) via the bites of infected Aedes albopictus mosquitoes. Half the horses were infected with a viral isolate from the brain of a horse (BC787), and half were infected with an isolate from crow brain (NY99-6625); both were NY99 isolates. Postinfection, uninfected female Ae. albopictus fed on eight of the infected horses. In the first trial, Nt antibody titers reached >1:320, 1:20, 1:160, and 1:80 for horses 1 to 4, respectively. In the second trial, the seven horses with subclinical infections developed Nt antibody titers >1:10 between days 7 and 11 post infection. The highest viremia level in horses fed upon by the recipient mosquitoes was approximately 460 Vero cell PFU/mL. All mosquitoes that fed upon viremic horses were negative for the virus. Horses infected with the NY99 strain of WNV develop low viremia levels of short duration; therefore, infected horses are unlikely to serve as important amplifying hosts for WNV in nature.     

Experimental transmission of St. Louis encephalitis virus by Ochlerotatus j. japonicus

Ochlerotatus japonicus japonicus a newly discovered nonindigenous mosquito species in North America, and a colonized strain of Culex pipiens were compared for their vector competence for St. Louis encephalitis virus (SLE). Infection rates in Oc. j. japonicus were 0-33% after feeding on chickens with viremias between 10(4.1) and 10(4.7) plaque-forming units (PFU)/ml of blood. In comparison, infection rates were 12-94% for Cx. pipiens that fed on the same chickens. When fed on chickens with viremias between 10(5.3) and 10(5.6) PFU/ml of blood, infection rates for Oc. j. japonicus and Cx. pipiens were similar, 96% and 100%, respectively. After 12-14 days of extrinsic incubation at 26 degrees C, all 34 infected Oc. j. japonicus had a disseminated infection. In contrast, only 23 (43%) of 54 infected Cx. pipiens had a disseminated infection after feeding on the same chickens. If they developed a disseminated infection, both species efficiently transmitted (> or = 87%) SLE. Estimated transmission rates at viral doses sufficient to infect both of the tested species were 29-84% for Oc. j. japonicus and 30-50% for Cx. pipiens. Because of its continued geographic expansion, field and laboratory evidence incriminating it as a vector of the closely related West Nile virus, and its ability to transmit SLE in the laboratory, Oc. j. japonicus should be considered as a potential enzootic or epizootic vector of SLE.     

Venezuelan equine encephalitis virus transmission and effect on pathogenesis

Quantifying the dose of an arbovirus transmitted by mosquitoes is essential for designing pathogenesis studies simulating natural infection of vertebrates. Titration of saliva collected in vitro from infected mosquitoes may not accurately estimate titers transmitted during blood feeding, and infection by needle injection may affect vertebrate pathogenesis. We compared the amount of Venezuelan equine encephalitis virus collected from the saliva of Aedes taeniorhynchus to the amount injected into a mouse during blood feeding. Less virus was transmitted by mosquitoes in vivo (geometric mean 11 PFU) than was found for comparable times of salivation in vitro (mean saliva titer 74 PFU). We also observed slightly lower early and late viremia titers in mice that were needle injected with 8 PFU, which represents the low end of the in vivo transmission range. No differences in survival were detected, regardless of the dose or infection route.     

Alligators as West Nile virus amplifiers

Recent evidence suggests that American alligators (Alligator mississippiensis) may be capable of transmitting West Nile virus (WNV) to other alligators. We experimentally exposed 24 juvenile alligators to WNV parenterally or orally. All became infected, and all but three sustained viremia titers >5.0 log10 PFU/mL (a threshold considered infectious for Culex quinquefasciatus mosquitoes) for 1 to 8 days. Noninoculated tankmates also became infected. The viremia profiles and multiple routes of infection suggest alligators may play an important role in WNV transmission in areas with high population densities of juvenile alligators.     

Vector competence of Aedes albopictus for a newly recognized Bunyavirus from mosquitoes collected in Potosi, Missouri

The vector competence of a Kentucky strain of Aedes albopictus was assessed for a newly recognized Bunyavirus isolated from Ae. albopictus collected in Potosi, Missouri. Females are susceptible to peroral infection and 44.7% became infected after ingesting about 15 Vero cell plaque-forming units (PFU) of virus. Virus replicated and reached average titers of 10(5.4)-10(6.0) PFU/mosquito by day 7 postfeeding. Fourteen (40%) of 35 females tested in an in vitro virus transmission experiment were infected, and 3 (21.4%) of the infected females transmitted virus. There was no evidence of vertical transmission among 1,196 progeny of a group of mothers exposed to infection perorally or among 6,635 progeny of mothers infected by parenteral inoculation. The absence or infrequency of vertical transmission suggests that the virus was not introduced into Missouri via infected Ae. albopictus eggs. Nonetheless, Ae. albopictus is a competent vector of this virus and we provide the first experimental evidence for incriminating Ae. albopictus as a vector in a natural arbovirus transmission cycle in the United States.     

Viraemic transmission of Crimean-Congo haemorrhagic fever virus to ticks

In order to determine the way in which vertebrates infected with Crimean-Congo haemorrhagic fever (CCHF) virus and potential ixodid tick vectors interact in nature, immature and adult ticks of several species were fed on viraemic mammals and then assayed for virus content at varying times after feeding. CCHF virus was not isolated from ticks of six species tested after feeding as adults and immature forms on sheep with viraemia of 10(2.5-3.2) LD 50/ml, nor from larval ticks fed on guinea-pigs and white-tailed rats with viraemia of 10(1.9-2.7) LD 50/ml. In contrast, virus was isolated from 10 of 152 pools of engorged adult ticks of 5 species that fed on cattle with viraemia of 10(1.5-2.7) LD 50/ml and from 3 of 137 female ticks after oviposition. Infection was transmitted to larval and nymphal Hyalomma truncatum and H. marginatum rufipes, but not to Rhipicephalus evertsi evertsi, from a scrub hare with viraemia of 10(4.2) LD 50/ml but only nymphal H. truncatum and H. m. rufipes became infected from scrub hares with viraemia of 10(2.6-2.7) LD 50/ml. Infection was transmitted trans-stadially in H. m. rufipes and H. truncatum infected as nymphae, and adult H. m. rufipes transmitted infection to a sheep. No evidence of transovarial transmission was found in larval progeny of ticks exposed to CCHF virus as adults on sheep and cattle or as immatures on scrub hares.     

Inactivation of human norovirus surrogates by benzalkonium chloride, potassium peroxymonosulfate, tannic Acid, and gallic Acid

Abstract Novel methods to effectively disinfect contact surfaces and prevent human norovirus transmission are essential. The effect of benzalkonium chloride (BAC), potassium peroxymonosulfate (KPMS), tannic acid (TA), and gallic acid (GA) on enteric virus surrogates, murine norovirus (MNV-1), feline calicivirus (FCV-F9), and bacteriophage MS2 was studied. Viruses at high (～7 log(10) PFU/mL) or low (～5 log(10) PFU/mL) titers were mixed with equal volumes of BAC (0.2, 0.5, and 1?mg/mL), KPMS (5, 10, and 20?mg/mL), TA (0.02 and 0.2?mg/mL), GA (0.2, 0.4, and 0.8?mg/mL), or water and incubated for 2?h at room temperature. Viral infectivity after triplicate treatments was evaluated using plaque assays in duplicate. Low titers of FCV-F9 and MNV-1 were completely reduced, while low-titer MS2 was reduced by 1.7-1.8 log(10) PFU/mL with BAC at all three concentrations. High-titer FCV-F9 was reduced by 2.87, 3.08, and 3.25 log(10) PFU/mL, and high-titer MNV-1 was reduced by 1.55, 2.32, and 2.75 log(10) PFU/mL with BAC at 0.1, 0.25, and 0.5?mg/mL, respectively. High-titer MS2 was reduced by ～2 log(10) PFU/mL with BAC at all three concentrations. KPMS at all three concentrations reduced high and low titers of FCV-F9 and MS2 and low-titer MNV-1 to undetectable levels, while high-titer MNV-1 was reduced by 0.92 and 3.44 log(10) PFU/mL with KMPS at 2.5 and 5?mg/mL, respectively. TA at 0.2?mg/mL only reduced high-titer FCV-F9 by 0.98 log(10) PFU/mL and low-titer FCV-F9 by 1.95 log(10) PFU/mL. GA at 0.1, 0.2, and 0.4?mg/mL reduced low-titer FCV-F9 by 2.50, 2.36, and 0.86 log(10) PFU/mL, respectively with negligible effects against high-titer FCV-F9. BAC and KPMS show promise to be used as broad-spectrum contact surface disinfectants for prevention of noroviral surrogate contamination.     

Mechanical transmission of lumpy skin disease virus by Aedes aegypti (Diptera: Culicidae)

Aedes aegypti female mosquitoes are capable of the mechanical transmission of lumpy skin disease virus (LSDV) from infected to susceptible cattle. Mosquitoes that had fed upon lesions of LSDV-infected cattle were able to transmit virus to susceptible cattle over a period of 2-6 days post-infective feeding. Virus was isolated from the recipient animals in 5 out of 7 cases. The clinical disease recorded in the animals exposed to infected mosquitoes was generally of a mild nature, with only one case being moderate. LSDV has long been suspected to be insect transmitted, but these findings are the first to demonstrate this unequivocally, and they suggest that mosquito species are competent vectors.     

Time-dependent effects of pomegranate juice and pomegranate polyphenols on foodborne viral reduction

Pomegranate juice (PJ) and pomegranate polyphenolic extracts (PP) have antiviral effects against HIV-1, influenza, herpes, and poxviruses, and we recently demonstrated their effect against human noroviral surrogates. In the present study, the time-dependent effects of two commercial brands of PJ and PP at two concentrations (2 and 4?mg/mL) on the infectivity of foodborne viral surrogates (feline calicivirus FCV-F9, murine norovirus MNV-1, and MS2 bacteriophage) at room temperature for up to 1?h were evaluated. Each virus at ～5 log(10) plaque-forming units (PFU)/mL was mixed with equal volumes of PJ, or PP at 4 or 8?mg/mL, and incubated for 0, 10, 20, 30, 45, and 60?min at room temperature. Viral titers after each treatment were determined by standardized plaque assays and compared with untreated controls. Virus titer reduction by PJ and PP was found to be a rather rapid process, with ≥50% of titer reduction occurring within the first 20?min of treatment for all three tested viruses. Within the first 20?min, titer reductions of 3.12, 0.79, and 0.23 log(10) PFU/mL for FCV-F9, MNV-1, and MS2, respectively, were obtained using PJ. FCV-F9, MNV-1, and MS2 titers were reduced by 4.02, 0.68, and 0.18 log(10) PFU/mL with 2?mg/mL PP and 5.09, 1.14, and 0.19 log(10) PFU/mL with 4?mg/mL PP, respectively, after 20?min. The mechanism of viral reduction by PJ and PP needs to be elucidated and clinical trials should be undertaken before recommending for therapeutic or preventive purposes.     

Experimental studies to determine the susceptibility to infection with St. Louis encephalitis virus of five species of Panamanian mosquitoes.

The susceptibility to infection with a Panamanian isolate of St. Louis encephalitis (SLE) virus was evaluated in Culex quinquefasciatus, Haemagogus equinus, Mansonia dyari, Sabethes cyaneus and Deinocerites pseudes. When fed on blood-virus suspensions using the hanging drop or pledget technique, the median infective dose (ID50) of SLE virus for colonized strains of Cx. quinquefasciatus and Hg. equinus was 10(2.8) plaque forming units (PFU)/2 microliters and 10(3.5) PFU/2 microliters, respectively. The susceptibility of F1 and F2 Cx. quinquefasciatus females was similar to the colonized strain by the same technique. When fed on viremic chicks, the ID50 for both Cx. quinquefasciatus and Hg. equinus was 10(0.5) PFU/2 microliters. These results and successful transmission trials indicate that both of these species have the potential to serve as vectors of SLE virus in Panama. Because of their poor feeding response, complete susceptibility profiles were not obtained for the other 3 species tested. They appear to be less susceptible than Cx. quinquefasciatus and Hg. equinus, although Ma. dyari was readily infected after engorging on a blood-virus suspension with a titer of 10(3.0) PFU/2 microliters.     

The significance of low density microfilaraemia in the transmission of Wuchereria bancrofti by Culex (Culex) quinquefasciatus Say in Sri Lanka

Laboratory-bred Culex quinquefasciatus were fed on carriers with low and moderate densities of microfilariae (mf) of Wuchereria bancrofti. In the first series of experiments, mosquitoes were dissected 12 d after feeding. The percentage of infected mosquitoes and the numbers of larvae per infected mosquito were directly proportional to the mf density at the time of feeding. There was an overall high infection rate and a wide distribution of larvae per individual mosquito at all levels, except for the 4 lowest counts. Of the 4 carriers with counts of 5 mf/ml and less, 3 were capable of infecting Cx quinquefasciatus, giving infection rates of 1.0%, 7.4% and 12.0% respectively. In the second series, some mosquitoes were dissected immediately after feeding and the remainder 12 d later. There was a good correlation between the number of mf ingested and the number of infective larvae per mosquito. The high infection rates in Cx quinquefasciatus when fed on low-density microfilaraemia carriers, and the varying number of larvae in individual mosquitoes, suggest that low-density carriers could be a source of infection. Field studies were also carried out in 3 different area with mf rates of 7.24%, 0.72% and 0.16%, respectively. In the 2 areas with low mf rates, infection rates in mosquitoes were 1.32% and 1.08% respectively. Cx quinquefasciatus fed on a carrier with a residual microfilaraemia of 19 mf/ml following treatment with diethylcarbamazine had an infection rate of 13.8%. These studies suggest that the examination of recently fed house-resting populations of Cx quinquefasciatus could be a sensitive method for measuring the prevalence of mf in the human population.     

Vector competence of geographic strains of Aedes albopictus and Aedes polynesiensis and certain other Aedes (Stegomyia) mosquitoes for Ross River virus

The vector competence of geographic strains of Aedes albopictus and Ae. polynesiensis and Fiji strains of Ae. pseudoscutellaris and Ae. aegypti was assessed for Ross River (RR) virus, the etiologic agent of epidemic polyarthritis. Strains of Ae. polynesiensis from Fiji, Rarotonga, Somoa and Tahiti were the most susceptible to infection per os (MID50 less than or equal to 10(1.2) Vero cell plaque-forming units [PFU]/blood meal). Virus transmission data were variable, but all strains except the one from Fiji transmitted virus at 14 to 21 days postinfection. Shanghai and Hawaii Ae. albopictus and Fiji Ae. pseudoscutellaris were also highly susceptible to per os infection with RR virus (MID50 10(2.0) to 10(2.6) PFU). Singapore and Sri Lanka Ae. albopictus and Fiji Ae. aegypti were the least susceptible (MID50 10(4.0) to 10(4.2) PFU). With one exception, virus transmission rates for Ae. pseudoscutellaris and Ae. aegypti and the four strains of Ae. albopictus ranged from 52 to 100%. A total of 4,718 third- and fourth-instar larvae from the second gonotrophic cycle of potentially infected females were tested for RR virus in 39 pools. Infection rates in parental females ranged from 87 to 100% in Ae. albopictus, Ae. pseudoscutellaris and Ae. polynesiensis and 40 to 48% in Ae. aegypti. Virus was not isolated from larval progeny.     

Replication, tissue tropisms and transmission of yellow fever virus in Aedes albopictus

Experimental studies undertaken to ascertain the dynamics of yellow fever virus replication in an introduced strain (Houston) of the Asian mosquito, Aedes albopictus (Skuse), indicate that this species is an efficient vector of yellow fever virus. Replication of virus in Ae. albopictus could be detected 3 d after feeding on a suspension containing 7.2 log10 Vero cell plaque forming units (PFU) per ml of virus; peak titres (3.5 log10 PFU/mosquito) occurred 7 d after exposure. Viral antigen, visualized by immunofluorescence, was first detected in midgut cells 4 d after exposure and appeared in fat cells 7 d after exposure. The only other mosquito tissues revealing viral antigen were the salivary glands, brain, and occasionally cells of the suboesophageal ganglion. Viral antigen was not detected in any of the tissues of the reproductive tract, nor could viral genomic ribonucleic acid (RNA) be detected in these tissues by RNA-RNA molecular hybridization in situ. We detected no vertical transmission of yellow fever virus in 6180 F1 adult progeny produced from infected females. The extrinsic incubation period at 26.7 degrees C was 9 d. We conclude that the Houston strain of Ae. albopictus is a competent vector of yellow fever virus and can serve as bridging vector between the jungle yellow fever cycle and the urban cycle in New World ecosystems.     

Absence of viraemia in cattle after experimental infection with Japanese encephalitis virus

Cow calves were infected with Japanese encephalitis virus (JEV) by parenteral inoculation. One batch was reinfected with JEV, followed by West Nile virus (WNV), while another batch was reinfected directly with WNV. No viraemia due to either JEV or WNV was demonstrated in any of the calves. Culex tritaeniorhynchus mosquitoes fed on 4 of the calves infected with JEV during the first 10 d had no detectable virus, nor did they transmit the virus by bite to susceptible baby chickens. In another experiment, calves did not develop viraemia after infected C. tritaeniorhynchus mosquitoes were allowed to feed on them. Neutralizing and/or haemagglutination-inhibiting antibodies against JEV were demonstrated in 6 of the 11 calves, which explains the high proportion of JE seropositives among cattle in India. All the 5 calves that were infected with WNV subsequent to JEV developed neutralizing and haemagglutination-inhibiting antibodies against WNV also. The study indicates that cattle do not play a role in the maintenance of JEV in nature.