Browsing by Author "Snowden, Karen F."

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    Biogeography and genetic variation of triatomine chagas disease vectors and trypanosoma cruzi isolates from texas
    (2009-05-15) Kjos, Sonia Alane; Coates, Craig J.; Olson, Jimmy K.; Craig, Thomas M.; Snowden, Karen F.; Teel, Pete D.
    Trypanosoma cruzi is endemic in the U.S., infecting humans, dogs, and wildlife. This study identified a new geographic distribution for triatomine species within Texas based on 2,449 records obtained from published data and new field studies. Triatomine vectors of T. cruzi were reported from 97 counties covering all ecological zones. Triatoma gerstaeckeri was the most commonly collected species followed by T. sanguisuga. New field collections resulted in 233 specimens from 37 counties and a 52% T. cruzi infection rate. A second trypanosome, Blastocrithida triatomae was found in two specimens from different locations. A habitat suitability model for T. gerstaeckeri was developed using GIS and remote sensing applications. Forest and rangeland were the predominant land cover classes found within T. gerstaeckeri habitat, where as water and agriculture proved to have little influence on habitat suitability. Genetic variation of seven triatomine species from Texas was evaluated using cytochrome b DNA sequences from 61 new specimens. This is the first study of the taxonomic status of T. gerstaeckeri, T. indictiva, and T. neotomae using molecular markers. Intraspecific variation for T. sanguisuga and T. gerstaeckeri suggests significant gene flow across their ranges within Texas. Genetic variation of T. cruzi isolates from Texas was evaluated using SSU rRNA gene sequences. Included were 63 new sequences from five triatomine species, canine, baboon, and human isolates. Sequences partitioned into two groups in agreement with previous studies on U.S. isolates. Genetic variation of T. cruzi did not occur according to host, geographic location, or collection site. The extent of Chagas disease in domestic canines of Texas is described by geographic distribution, signalment, and clinical presentation and histopathology. Based on data from 553 cases, the geographic distribution in Texas is widespread (46 counties) and closely matches the distribution of the Triatomine vectors. Chagas disease was diagnosed in 33 breeds, primarily sporting/working dogs. This study represents the most comprehensive characterization of components of the Chagas disease transmission cycle in the U.S. to date. These findings should raise awareness among physicians, veterinarians, and public health practitioners regarding T. cruzi, its vectors, canine infection, and human risk for Chagas disease in Texas.
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    Coccidian Parasites and Conservation Implications for the Endangered Whooping Crane (Grus americana)
    (PLOS, 2015-10-10) Bertram, Miranda R.; Hamer, Gabriel L.; Snowden, Karen F.; Hartup, Barry K.; Hamer, Sarah A.
    While the population of endangered whooping cranes (Grus americana) has grown from 15 individuals in 1941 to an estimated 304 birds today, the population growth is not sufficient to support a down-listing of the species to threatened status. The degree to which disease may be limiting the population growth of whooping cranes is unknown. One disease of potential concern is caused by two crane-associated Eimeria species: Eimeria gruis and E. reichenowi. Unlike most species of Eimeria, which are localized to the intestinal tract, these crane-associated species may multiply systemically and cause a potentially fatal disease. Using a non-invasive sampling approach, we assessed the prevalence and phenology of Eimeria oocysts in whooping crane fecal samples collected across two winter seasons (November 2012–April 2014) at the Aransas National Wildlife Refuge along the Texas Gulf coast. We also compared the ability of microscopy and PCR to detect Eimeria in fecal samples. Across both years, 26.5% (n = 328) of fecal samples were positive for Eimeria based on microscopy. Although the sensitivity of PCR for detecting Eimeria infections seemed to be less than that of microscopy in the first year of the study (8.9% vs. 29.3%, respectively), an improved DNA extraction protocol resulted in increased sensitivity of PCR relative to microscopy in the second year of the study (27.6% and 20.8%, respectively). The proportion of positive samples did not vary significantly between years or among sampling sites. The proportion of Eimeria positive fecal samples varied with date of collection, but there was no consistent pattern of parasite shedding between the two years. We demonstrate that non-invasive fecal collections combined with PCR and DNA sequencing techniques provides a useful tool for monitoring Eimeria infection in cranes. Understanding the epidemiology of coccidiosis is important for management efforts to increase population growth of the endangered whooping crane.
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    Estimating the Burden of Neurocysticercosis in Mexico
    (2012-10-19) Bhattarai, Rachana; Budke, Christine M.; Carabin, Hélène; Ivanek-Miojevic, Renata; Snowden, Karen F.
    Neurocysticercosis (NCC) is a parasitic disease caused by the larva of the zoonotic cestode Taenia solium. The objectives of this study were to evaluate the distribution of presenting clinical manifestations of NCC, to evaluate the socio-demographic characteristics of NCC patients, to compare quality of life of individuals diagnosed with NCC with an age and sex matched control population and to estimate the non-monetary burden of NCC in Mexico. In order to accomplish these objectives, a case series of NCC patients was conducted in two neurology referral hospitals in Mexico City, Mexico during 2007-2008. Information on clinical manifestations associated with NCC was obtained via medical chart reviews of NCC patients. Information on socio-demographic characteristics of NCC patients was obtained through the administration of questionnaires. In addition, a cross-sectional study was conducted to compare the quality of life of NCC patients to an age and sex matched control population using the short form 12 v2 (SF-12 v2) survey. Non-monetary burden of NCC in Mexico was estimated using disability adjusted life years (DALYs), incorporating morbidity due to both NCC-associated epilepsy and severe headache and mortality due to NCC-associated epilepsy. NCC patients presented to the neurology referral hospitals with numerous clinical manifestations, with severe headache and epilepsy being the most common. Lack of knowledge of T. solium transmission was common among NCC patients, with 25 percent of patients not knowledgeable about tapeworm infections in humans. Of those that were aware that tapeworm infections do occur, 57 percent were not aware of how the worms were transmitted to humans. The SF-12 v2 general health survey showed that individuals with NCC had a significantly lower score for all eight domains of health evaluated (physical functioning, role physical, bodily pain, vitality, general health, social functioning, role emotional and mental health) compared with the age and sex matched population from the same region (p< 0.05). The mean total number of DALYs lost due to NCC in Mexico was estimated to be 99,866 (95 percent CR: 43,187 –189,182), with a mean of 0.95 (95 percent CR: 0.4–1.8) DALYs lost per thousand persons per year.
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    Estimating the Non-Monetary Burden of Neurocysticercosis in Mexico
    (PLoS Neglected Tropical Diseases, 2012) Bhattarai, Rachana; Budke, Christine M.; Carabin, Hélène; Proaño, Jefferson V.; Flores-Rivera, Jose; Corona, Teresa; Ivanek, Renata; Snowden, Karen F.; Flisser, Ana; Zinsstag, Jakob
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    Molecular and in vitro characterization of a Babesia divergens-like agent from eastern cottontail rabbits (Sylvilagus floridanus) on Nantucket Island
    (Texas A&M University, 2006-10-30) Spencer, Angela M; Holman, Patricia J.; Craig, Tom M.; Magill, Clint; Snowden, Karen F.
    A Babesia sp. isolated from eastern cottontail rabbits (Sylvilagus floridanus) is morphologically similar and genetically identical, based on SSU rRNA gene comparisons, to two agents responsible for human babesiosis in North America and is closely related to the European parasite, Babesia divergens. The ribosomal RNA (rRNA) internal transcribed spacer regions (ITS1 and ITS2) and the 5.8S rRNA genes of Babesia isolates were sequenced and analyzed. The rRNA ITS region sequences of three isolates, one each from Kentucky, Massachusetts and Great Britain, considered Babesia divergens-like organisms, were compared to two Babesia microti isolates, two Babesia odocoilei isolates and a well defined Babesia divergens isolate. The two B. divergenslike isolates from North America shared identical rRNA ITS1-5.8S-ITS2 region sequences, and the clones of these isolates clustered into one clade in three phylogenetic analyses, suggesting that these isolates are conspecific. In vitro comparison of host erythrocyte specificity between the rabbit Babesia sp. and B. divergens was employed to discriminate between the two organisms and to determine the usefulness of in vitro techniques for Babesia sp. characterization. In vitro growth of the rabbit Babesia sp. was supported in human and cottontail rabbit erythrocytes, but not in bovine cells. Babesia divergens in vitro growth was supported in human and bovine erythrocytes, but not in cottontail rabbit cells. Morphological characteristics and size differences also distinguished the two parasites from one another. The erythrocyte specificity and parasite size differences reported in this study agree with previous in vivo results and validate the use of in vitro methods for characterization of Babesia species.
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    Molecular and in vitro growth comparisons of Encephalitozoon hellem isolates from human and bird hosts
    (Texas A&M University, 2004-09-30) Waters, Paulette Francesca; Holman, Patricia J.; Abbott, Louise C.; Snowden, Karen F.
    Molecular and in vitro comparisons were performed using two isolates of Encephalitozoon hellem, one from an avian host and one from a human host, and one isolate of Encephalitozoon cuniculi from a rabbit. The molecular comparisons were performed by amplifying and sequencing the gene coding for a zinc metallo-aminopeptidase from cDNA and gDNA obtained from each of the isolates. The E. hellem sequences shared >99 % identity between each other and 70% identity with the E. cuniculi sequences. Conserved HEXXH and GXMEN motifs located within the sequences classify the protein as an aminopeptidase of the M1 family, with at least one zinc atom required for catalytic activity. In vitro growth comparisons of the isolates described above were performed under simulated "mammalian and avian conditions". The models utilized mammalian and avian cell lines and sera at incubation temperatures of 37 °C and 40 °C, respectively. Three separate experiments were performed. E. cuniculi grew best under the mammalian model and significantly better than both E. hellem isolates under this model. The E. hellem isolates were able to infect and replicate under both the mammalian and avian models, which reflects the zoonotic potential of these isolates.