Farida Mahmood

Western Equine Encephalomyelitis Virus Infection Affects the Life Table Characteristics of Culex tarsalis (Diptera: Culicidae)

Abstract The life table attributes of Culex tarsalis Coquillett females infected experimentally by feeding on 4 and 6 log10 plaque-forming units (PFU) of western equine encephalomyelitis virus (WEEV) per milliliter of heparinized chicken blood were compared with an uninfected control group. Females continually were offered 10% sucrose and an oviposition substrate and daily a blood meal through a biomembrane feeder. Mortality (dead females) and fecundity (female eggs per female) were monitored daily until all females died. Overall, 94% of 198 females in the two virus-infected groups were positive for WEEV at death when tested by plaque assay; the average body virus titer at death did not differ between groups. WEEV infection significantly altered the life table characteristics of Cx. tarsalis. Life expectancy at infection in days (ex), reproductive effort in female eggs per female per generation (Ro), and generation time (T) in days for the infected cohorts were significantly lower than for the uninfected controls, whereas the reproductive rate (rc) in female eggs per female per day was higher for infected than uninfected cohorts. In agreement with the WEEV infection data that showed similar body titers, there were few differences between the life table parameters for the 4 and 6 log10 PFU treatment groups. Greatest differences were observed for survivorship between days 17–40 when virus titers in infected dying females were greatest. Our data extend recent studies that indicate mosquito infection with encephalitis viruses has a cost of reduced life expectancy and fitness.

Role of Nestling Mourning Doves and House Finches as Amplifying Hosts of St. Louis Encephalitis Virus

Abstract Nestling mourning doves and house finches produced elevated viremias after inoculation with 2–3 log10 plaque-forming units (PFU) of St Louis encephalitis (SLE) virus and infected 67 and 70% of Culex tarsalis Coquillett that engorged upon them, respectively. Mosquito infection rates as well as the quantity of virus produced after extrinsic incubation increased as a function of the quantity of virus ingested and peaked during days 3–5 postinoculation in mourning doves and days 2–4 in house finches. Only female Cx. tarsalis with body titers ≥4.6 log10 PFU were capable of transmitting virus. Overall, 38% of females infected by feeding on mourning doves and 22% feeding on house finches were capable of transmission. The quantity of virus expectorated was variable, ranging from 0.8 to 3.4 log10 PFU and was greatest during periods when avian viremias were elevated. Our data indicated that nestling mourning doves and house finches were competent hosts for SLE virus and that the quantity of virus ingested from a viremic avian host varies during the course of the infection and determines transmission rates by the mosquito vector.

Anopheles culicifacies: effects of age on the male reproductive system and mating ability of virgin adult mosquitoes

Abstract. Under controlled laboratory conditions of 28–30oC and 16:8 L:D photoperiod, an attempt was made to develop an age‐grading technique for Anopheles culicifacies males. Mating activity was maximal when females were 5–12 days old and males were 5–7 days old. The numbers of total and mature spermatocysts declined significantly with age, and the proportion of the testes occupied by the sperm reservoir increased as virgin males grew older. Mating resulted in the loss of spermatozoa and accessory gland substance from the reproductive system. Loss of mating ability of older virgin males seemed to be age‐related, because the reproductive system contained ample supplies of accessory gland substance and spermatozoa. Morphological changes of the reproductive system, due to mating and age, were used to infer the age and reproductive history of unknown males in a laboratory evaluation.

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

ABSTRACT The vector competence of Culex tarsalis Coquillett for the BFS1703 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), females of the susceptible high virus producer (HVP) strain rapidly amplified 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.

Previous Infection Protects House Finches from Re-Infection with St. Louis Encephalitis Virus

Abstract Antibody titers against St. Louis encephalitis virus (SLE) measured by a plaque reduction neutralization test (PRNT) decreased rapidly in house finches (Capodacus mexicanus) after initial infection, whereas antibodies measured by enzyme immunoassay (EIA) remained detectable in all birds for the length of the experiment, indicating long-term persistence and greater assay sensitivity of the EIA. After 52 wk, birds were challenged by subcutaneous inoculation with the same strain of SLE virus. Virus was not detected for 1–4 d postchallenge in blood samples tested by plaque assay and RT-PCR or by xenodiagnosis in Culex tarsalis fed concurrently and then held for 11 d at 26°C. Virus was detected by all three methods in control birds infected concurrently for the first time. Challenge with SLE produced a rapid and marked ananmestic rise in both neutralizing and EIA antibody titers that exceeded the primary response in the same birds or in concurrently inoculated control birds. At necropsy 4 wk postchallenge, 3 of 7 challenged and 1of 2 positive control birds were chronically infected, with viral RNA detected by RT-PCR in brain, spleen, lung, and/or kidney tissues. Our results indicated that persistence of protective antibody prevents reinfection during the following season and may prevent the recrudescence of infectious virus in chronically infected birds.

Effects of immunosuppression on encephalitis virus infection in the house finch, Carpodacus mexicanus

Abstract Immunosuppression of house finches was attempted by blood feeding Culex tarsalis Coquillett mosquitoes or by injecting birds with the corticosteroid dexamethasone or the immunosuppressant drug cyclophosphamide before and after inoculation with western equine encephalomyelitis or St. Louis encephalitis viruses. Mosquito bites (8–37 females blood feeding on each bird over a 3-d period) did not enhance the viremia response or increase the frequency of chronic infection. In contrast, dexamethasone and cyclophosphamide enhanced the amplitude and duration of the viremia response, but had no consistent effect on the antibody responses as measured by enzyme immunoassay or plaque reduction neutralization assay. Elevated viremias were followed by increases in the frequency of chronic infections with St. Louis encephalitis, but not western equine encephalomyelitis. Immunosuppression may provide a useful tool to study the chronic infection process of flaviviruses in vertebrates.

Survey of Mosquito Fauna in San Antonio, Texas

Abstract A faunal survey of mosquitoes was conducted in 2008, 2009, and 2010 at various trapping locations throughout the city of San Antonio, TX. A total of 22,739 mosquitoes representing 41 species in 8 genera were collected during this study. The most prevalent mosquito species collected were Aedes vexans (25%), Ae. sollicitans (14%), Culex tarsalis (13.5%), and Cx. erraticus (11%). Four mosquito species (Ae. bimaculatus, Anopheles freeborni, Cx. declarator, and Psorophora horrida) not previously recorded in this area were collected, whereas several species historically occurring in San Antonio were not collected during this survey.

Description of a Culex pipiens gynandromorph from New York City.

ABSTRACT Morphology and internal anatomy of a Culex pipiens L. bipolar gynandromorph that was collected on September 3, 2005 in a gravid trap at Springfield Park in the borough of Queens, New York City, NY is presented. The head of the mosquito possessed male palpi, compared to the rest of the body, which had female anatomical and morphological characteristics. The relation of morphological characteristics to physiological responses of the gynandromorph is discussed.

MORPHOLOGICAL VARIANTS OF AEDES SOLLICITANS FROM NEW JERSEY

ABSTRACT Morphological variants showing differences in length of median white scaled bands on the proboscises of female Aedes sollicitans (Cape May County, NJ) are described from F1 progeny of wild-caught mosquitoes. The length of the white-scaled band was classified into 5 categories: 1) large (0.53–0.60 mm), 2) medium (0.40–0.47 mm), 3) small (0.27–0.33 mm), 4) very small (0.13–0.20 mm) band to a patch of scales on the lateral aspect, and 5) a black proboscis Misidentification of adults during surveillance can be avoided by using other species-specific characters for Ae. sollicitans lacking a white-scaled band on the proboscis.