UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
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Item Feeding behavior and distribution of Varroa destructor on adult bees of Apis mellifera(2022) Lamas, Zachary Siqueira; Hawthorne, David J; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Varroa destructor is a competent vector of honey bee viruses and the leading cause of colony losses worldwide. Much about its feeding behavior and distribution on adult bees remains unknown. This work shows that Varroa are promiscuous feeders of adult bees, actively switching from one host to another. Laboratory trials showed there is a large heterogeneity in the host switching rate with some Varroa switching infrequently while others switched at high rates. The consequences of Varroa feeding on adult bees is largely unknown because adult feeding has largely been overlooked. This work shows that there is a high relative risk of death from Varroa feedings. Adult workers die quickly without developing high levels of infection after being fed upon by an infectious Varroa, and confer lower risk to their non-parasitized nestmates than counterparts which were nestmates to longer lived parasitized bees. Further experiments showed communicable routes of virus transmission may explain these findings. Trophallaxis between adult workers allowed for the movement of the pathogen to naïve nestmates. These nestmates act as an infectious reservoir to naïve Varroa showing communicable transmission between hosts can influence the acquisition and subsequent vectoring of the same pathogen by the vector. Another social behavior, cannibalization, was shown to have the same influence on Varroa vectoring. Varroa were also shown to be susceptible to viral acquisition through shared feedings on adult bee and brood hosts. Naïve Varroa readily acquired and then transmitted deformed wing virus when sharing the same host with an infectious Varroa. Collectively this work exemplifies how host social behavior and Varroa-Varroa transmission routes can increase the risk of vectors becoming infectious. Varroa feedings and virus transmission on adult workers cannot describe one of the most glaring features of Varroa infestations. For a portion of the year Varroa aggregate predominantly on adult drones, largely ignoring the worker cohort. Parasite burden only shifts onto workers when drone production ceases.Item ESTIMATING RISK OF AIRBORNE INFLUENZA TRANSMISSION IN A CONTROLLED ENVIRONMENT(2019) Bueno de Mesquita, Paul Jacob; Milton, Donald K.; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Pandemic preparedness is weakened by uncertainty about the relative importance of influenza transmission modes, particularly airborne droplet nuclei (aerosols). A human-challenge transmission trial in a controlled environment was conducted to address this uncertainty. Healthy, seronegative volunteer ‘Donors’ (N=52) were randomly selected for intranasal challenge with influenza A/Wisconsin/67/2005 (H3N2) and exposed to seronegative ‘Recipients’ randomized to intervention (N=40) or control (N=35) groups. Intervention recipients wore face shields and hand sanitized frequently to limit large droplet and contact transmission. A transmitted infection, confirmed by serology in a control recipient, yielded a 1.3% SAR overall. This was significantly less than the expected 16% SAR (p <0.001) based on a proof-of-concept study that used half as many Donors and exposure days. The main difference between these studies was mechanical building ventilation in the follow-on study, suggesting a possible role for aerosols. The extent to which Donor viral shedding was similar to that of mild, natural infections and may be useful for studying transmission was investigated. The only available aerosol shedding comparison data comes from a population of adults with influenza A H3 infection enrolled on the basis of febrile illness plus cough or sore throat, or positive Quidel QuickVue rapid test (N=83). Systematic differences in case selection compared with Donors yielded more severe cases and introduced bias. To account for differences in illness severity, propensity score matching, stratification, and inverse weighting ultimately demonstrated that the experimental and naturally infected groups were too different to compare without bias. While acknowledging the uncertainty in the generalizability of the current challenge model, observed aerosol shedding and CO2 were used in the rebreathed-air version of the Wells-Riley equation to compute average quantum generation rates (95% CI) 0.029 (0.027, 0.03) and 0.11 (0.088, 0.12) per hour for infected Donors and fine aerosol shedding Donors, respectively. Donors shed 1.4E+5 (1.0E+5, 1.8E+5) airborne viral RNA copies per quantum (ID63). This dissertation provides evidence for airborne transmission, presents a methodology for estimating an airborne dose, and suggests a role for building ventilation in reducing risk and the need for future observational studies to evaluate transmission modes in non-experimental settings with greater generalizability.Item Adaptation of A/Mallard/Potsdam/178-4/83 (H2N2) in Japanese quail leads to Replication and Transmission in Chickens(2005-05-02) Sorrell, Erin Maureen; Perez, Daniel R; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Influenza is a single stranded, negative-sense RNA virus with a segmented genome that can infect avian and mammalian species. Influenza viruses from the avian reservoir do not seem to replicate efficiently in humans upon direct transmission. Therefore, an intermediate host is involved in generating mutations to create a more transmissible or an avian-human reassortant virus. Quail have been highlighted as a potential reservoir and intermediate host of avian influenza. To assess the potential of quail as an intermediate host, A/Mallard/Postdam/178-4/83, H2N2 was tested to determine if through adaptation in quail a mallard strain can replicate and transmit in quail, as well as other avian species. After six serial passages of lung homogenate a virus arose, which replicated and transmitted directly to contact quail. When chickens were infected with this quail-adapted virus replication and transmission were observed, while no replication was noted in the chickens infected with wild type H2N2 virus.