The role of bacteria in mosquito development: a comparative study of distantly related species

Molly Hancuh, a student from University of Minnesota-Morris, worked with Bret Boyd and Ruby Harrison in the lab of Dr. Mike Strand to examine the role of bacteria in mosquito larval development.

Abstract: The digestive tract of a mosquito is home to bacterial community that is essential for normal development (1). In the larval stages, bacteria stimulate molting and growth (1). Some members of the larval gut community persist into the adult mosquito where they influence reproduction and ability to vector pathogens (2,3). Previous studies on the role of gut- bacteria in development have focused on the genus Aedes, including Aedes aegypti, which transmits the pathogens that cause Dengue fever and Zika virus syndrome. It is unknown if findings from Aedes species apply to all mosquitoes. Here, we address two important findings from Aedes in distantly related genus Anopheles by studying the malaria vectors An. gambiae and An. stephensi. First, we asked if Anopheles need bacteria to develop and if so, can we rescue development with individual bacterial species? Second, we assessed whether bacterial abundance in the guts of adult Ae. aegypti and An. gambiae differ before and after females blood feed. Like Ae. aegpyti, we find that bacteria free larvae cannot develop, however unlike Ae. aegypti some bacterial species cannot fully rescue larval development in Anopheles. Additionally the results were not equivocal between An. gambiae and An. stephensi. In adult mosquitoes, the bacterial community in the digestive tracts of Ae. aegypti and An. gambiae also responded differently to blood feeding. Collectively we find that that are commonalities between Aedes and Anopheles, however there were significant differences as well.

Download (PDF, 5.08MB)

Resource shifts and infectious disease dynamics in urbanized bird popualtions

Katie Adkins, a student from Clemson University, participated in an ongoing study of infectious disease dynamics in urban bird populations, supervised by Drs. Sonia Hernandez and Michael Yabsley.

Many wildlife species benefit from novel resources – especially supplemental food – offered in human-altered habitats. Shifts in wildlife ecology in response to intentional or accidental feeding can dramatically alter infectious disease dynamics. If hosts aggregate near resources and interact with novel species, provisioning can increase contact rates and exposure to pathogens. Concentrated resources could also improve host immune defenses, and dietary changes might alter the host’s microbiome, with downstream effects on pathogen invasion. Depending on the strengths of these relationships, provisioning could cause some pathogens and parasites to increase and others to decline. The goal of the overarching project is to examine how host use of anthropogenic resources influences pathogen and parasite dynamics across organizational scales. Specifically, our research explores interactions between an enteric pathogen, Salmonella, and the American White Ibis in South Florida, a recently urbanized species, to understand how resource shifts in urban habitats alter host ecology and pathogen dynamics.


Pathogen co-infection patterns within domestic dogs in rural environments

Djion Holness, a student from the University of Connecticut, worked with Amaka Nina Ananaba in the lab of Dr. Nicole Gottdenker to examine pathogen co-infection in dogs.

Abstract: Pathogens can interact with each other within a host, which can influence patterns of co-infection in populations by complex interactions within the host’s immune system, such as immunosuppression caused by infection with one pathogen which may influence susceptibility to infection with other pathogens. Furthermore, behavioral and environmental factors, such as habitat-associated contacts with a vector, can influence patterns of host co-infection. The objective of this study is to evaluate pathogen coinfection patterns in domestic dogs that live in rural communities occurring across a gradient of deforestation in rural Panama. The pathogens studied in the dogs included a mosquito-borne nematode (heartworm, dirofilaria), a triatomine vector-borne protozoan pathogen Trypanosoma cruzi , a sandfly transmitted protozoan pathogen (cutaneous leishmaniasis), and canine distemper virus. Data was collected from about 275 domestic dogs from 6 communities surrounded by distinct levels of deforestation (2 highly deforested, 2 moderately deforestated, 2 surrounded by forests), to the east and west of the
Panama Canal. Serologic tests were used to evaluate pathogen exposure and/or presence. Using a generalized linear mixed model there was no significance association between pathogen species richness and habitat type. A co-occurence model showed that there were no pathogen co-infections that occurred greater or less than expected due to chance. Results suggest that infection patterns of pathogens in this study are driven more by environmental factors and that there is little interaction between co-infecting pathogens in the studied dog populations.

Download (PDF, 1.1MB)


Natural history and genetic diversity of Dracunculus spp.

Alec Thompson, a Microbiology major from the University of Oklahoma, worked in the lab of Dr. Michael Yablsey to increase understanding of the genetic diversity of a parasite.

Abstract: Dracunculus spp. are spiruroid nematode parasites that live in the subcutaneous tissues or abdominal cavity of mammals. The most important species is D. medinensis, the human Guinea Worm. In 1985, over 3.5 million people were infected, but due to control efforts by the Carter Center and public health agencies, there were only 22 cases in 2015. Control was primarily through the use of water filters. A related species, D. insignis, is found in various wildlife species, and rarely dogs and cats, in North America. We have been conducting studies on D. insignis as a model parasite to better understand the ecology of D. medinensis. In this study, various potential vertebrate hosts were examined to determine the host-parasite interactions and genetic diversity of Dracunculus parasites within the United States. Analysis of the preliminary results suggests that the raccoon (Procyon lotor) is the preferential host for the parasite but opossums (Didelphis virginiana) are often frequently infected. Molecular characterization was attempted to investigate the intraspecific variation between hosts and regions and also to definitively identify adult female worms which cannot be identified using morphologic characteristics. However, the PCR was problematic as low specificity was observed with the PCR primers we used. Most sequencing attempts were either host DNA or mixed products.  We did get amplicons from four worms that were parasite DNA and they were all D. insignis. Methods for better specificity and amplification and other gene targets of are currently being researched and results are pending. Finally, we conducted experimental infection trials to investigate the potential role of amphibians and fish as hosts. Several species of amphibians were exposed to copepods infected with D. insignis. Infections of 2 species of tadpoles (gray tree frog and northern cricket frog) were confirmed by necropsy. These parasites were fed to ferrets and results will take 6-8 months. Bufo tadpoles did not consume copepods. Previous studies suggested that fish did not become infected with larvae, but we investigated the possible role as a transport host. Three species of fish (tilapia, fathead minnows, and gambusia) were exposed to infected copepods and then immediately fed to ferrets. Ferrets will be tested after 6-8 months. Although results of several studies are pending, this study has provided new data on the natural history of D. insignis and intiated additional studies that may help understand the continued transmission of D. medinensis by the use of alternative hosts.

Download (PDF, 751KB)

Improving Temperature Specific Data Used to Determine Transmission Risk for Malaria

Temitayo Adanlawo, a Biology major from Howard University, worked with Kerri Miazgowicz in the lab of Dr. Courtney Murdock to study an important disease vector.

Abstract: Malaria is a disease endemic to sub-Saharan Africa, India, southeast Asia and parts of Central and South America, and affects 300-600 million people every year. Malaria is a temperature-sensitive disease that varies between species. Currently, there is a disconnect between malaria transmission risk models and actual malaria incidence. This is due to species temperature-specific data substitution which increases uncertainty in results for the transmission risk equation (R0). In order to increase the accuracy of the temperature-dependent malaria transmission risk equation, a life table study was performed on Anopheles stephensi mosquitoes Using thirty mosquitoes at each of six different temperatures (16 °C, 20 °C, 24 °C, 28 °C, 32 °C, 36 °C), mortality, fecundity, and bite rate were recorded daily. Mosquitoes were given the opportunity to feed for fifteen minutes daily. We used the results of this study to create a thermal performance curve to determine a minimum, optimal, and maximum point for thermally-dependent malaria transmission risk and decrease overall malaria transmission risk uncertainty. Bite rate increased with temperature, as did fecundity. We concluded that the three variables study are, in fact, extremely temperature dependent and that mortality plays a huge role in the development of bite rate and fecundity.

Download (PDF, 1.24MB)


Geographic variation of Wolbachia-induced cytoplasmic incompatibility in the fly Drosophila recens

Sydney Keane, a Biology and Chemistry major from East Texas Baptist University, worked with Dr. Kelly Dyer examining the effects of infection on reproduction in Drosophila.

Abstract:  are bacterial parasites that commonly infect arthropods and nematodes. These parasites have damaging effects on the progeny of those they infect, including cytoplasmic incompatibility (CI). CI occurs when an infected male and an uninfected female mate, resulting in fewer eggs that successfully hatch into larvae than normal. In this study, infected virgin males from Drosophila recens were collected from multiple strains across three locations, and coupled with uninfected virgin females from the same species. After allowing the females to lay eggs for 72 hours, I recorded the numbers of eggs that hatched and that did not hatch. Males were tested for Wolbachia infection using PCR. After analyzing the data, I found that the overall hatch rate in each location was low, the amount of CI in each location did not vary significantly, the amount of CI in the experimental group compared to the control was significantly high, and that the number of total eggs produced varied significantly between the locations. The overall percentage of CI found within all of the locations examined was approximately 72%. These results show that the presence of Wolbachia is similarly effecting various populations of the fly throughout North America and that the level of CI occurring within this species may cause a drastic decrease in the population size over time.


Download (PDF, 2.79MB)

Surviving in Isolation: Are the Chilean Patagonia South American fur seals doomed to succumb to parasitic infections?

Kennesaw State University Biology Major Victoria Mendiola, worked in the lab of Dr. Nicole Gottdenker to study hookworm infectioun in South American fur seals.

Abstract: Hookworm infection is endemic in many otaiird species and can cause up to 70 % pup mortality in some populations (Lyons 2001, Seguel in press). South American fur seal (SAFS) neonates are able to clear hookworm infection in a matter of months, which is vital for pup survival (Seguel in press). Regardless of the significance of parasite clearance, little is known about the mechanisms involved in this process in wild populations. The aim of this research was to identify the mechanisms the fur seal pups use to expel the hookworms. In order to do so, the immune response was split into cell mediated and humoral responses.  Blood and hookworm samples were collected from Guafo Island, Chile during breeding seasons 2013 to 2015, with the inclusion of a control group (treatment of SAFS with Invermectin) starting in 2014. Blood smear slides were used for differential counting of leukocytes (cellular immune response), which was performed at the University of Georgia by standard methods. To detect antibodies in SAFS pup against hookworm parasites (humoral immune response), sections of Uncinaria sp. nematodes were incubated with sera from a pup that had successfully expelled the hookworms. The SAFS antibodies were labeled and visualized by standard immunohistochemistry techniques. Our examination of blood smears found there is a proportional increase in the number eosinophils with the severity of hookworm infection. The number of basophils and lymphocytes were highest in the group with mild hookworm infection, which suggests these leukocytes could play a role on regulating the severity of the hookworm infection. We also found evidence that the pups are able to produce an antibody that binds to in intestinal tract of the hookworm. The identification of fur seal antibodies reacting to the brush borders of the hookworm’s gastrointestinal tract suggests this is a necessary immune response for the fur seals to successfully expel the hookworms. In conclusion, we believe that a combination of these immune responses contribute to the successful expulsion of the parasite. The Chilean population of South American fur seals has declined more than 50% over the last 20 years. The most important breeding colony in Chile is located on Guafo Island, a remote island in the Northern Patagonia. Although this isolated population of fur seals lives in a very diverse and rich marine ecosystem, it has been in unrecoverable decline. The loss of genetic diversity is one of the consequences that face isolated mammal populations and low genetic variability has been associated with detrimental effects on marine mammals’ health (Acevedo et al. 2006). On Guafo Island, our prior research shows that hookworm infection is the major cause of pup mortality (Seguel et al. 2013) and that survival of hookworm infection is strongly mediated by the immune response to the parasite (Seguel et al. in preparation). Since the immune response is strongly linked to genetic variability, isolated populations are exposed to the expression of deleterious gene copies, which can limit the capacity to respond against parasites. Our hypothesis is that limited variability of the fur seal immune system genes is associated with susceptibility to hookworm disease. To test this we will extract DNA from fur seal skin samples and the genetic variability of each individual will be assessed by genotyping microsatellites loci cloned based on sequences published for other pinniped species and the MHC class II DQB locus. We expect to find lower genetic variability in animals with higher parasitic burden and clinical disease due to hookworms. Our student work will be centered on DNA extraction and PCR for the amplification of MHC II genes and later analyses of the sequence data.

Download (PDF, 1.75MB)


Microclimate affects mosquito body size

Nicole Solano, a dance and biology major from Agnes Scott College,  worked with Michelle Evans in the lab of Dr. Courtney Murdock to examine the effects of temperature on mosquito life history traits.

Abstract: The Asian Tiger mosquito, Aedes albopictus, is an invasive mosquito vector that can transmit up to 27 different arboviruses. Since mosquitoes are small ectotherms, variations in temperature largely impact their physiology, development, and potential to transmit human pathogens. Small changes due to microclimate significantly impact mosquito life history traits relevant for transmission (i.e. body size). Body size is an indicator of fecundity, population growth, and mosquito immunity; therefore understanding the effect of microclimate can inform small-scale variation in disease transmission. Last summer, a study was conducted to test the relationship between microclimate and body size in a semi-field system. They found that mosquitoes in urban sites were significantly smaller than those in rural sites; most likely due to warmer temperatures in urban sites.  To validate these findings in the field, we conducted field mosquito surveys and quantified Ae. albopictus wing length across land use.


Download (PDF, 2.29MB)

Using Environmental and Natural History Traits to Predict On-going Global Amphibian Die-offs

Kristina Frogoso, a student from the University of Arkansas at Little Rock, worked with Dr. Scott Connelly to examine the threat of a fungal pathogen to amphibian populations.

Abstract: Biodiversity loss is occurring in substantial rates, and more specifically we are seeing major amphibian declines due to infectious diseases. One infectious disease in particular is chytridiomycosis which is caused by a fungal pathogen called Batrachocytrium dendrobatidis (Bd). In order to predict future amphibian die-offs and prevent population decline using conservation methods, it is necessary to understand environmental variables and natural history traits in relation to Bd. The question is what variables are significant predictors of die-offs? A multiple linear regression (logit) was generated on RStudio to model the relationship first between environmental variables and then with added natural life history traits as the explanatory variables and threat status as the response variable. The threat status for species that had unknown threat status was predicted with 77% accuracy. Also, breeding site showed the most significant in predicting threat status of amphibian species, p < 0.5. The results show that species living in more permanent bodies of water tend to be more threatened that species that live in ephemeral sites. In conclusion, more information for other amphibian species and more thorough integration of trait data are needed to better predict population decline.


Download (PDF, 1.22MB)

Is the Transmission Rate of The Wolbachia Parasite Lower in Hybrids Compared To Pure Species?

Jasmine Gipson, from Kennesaw State University, worked with Dr. Kelly Dyer in the UGA Genetics department to study the transmission of Wolbachia, a parasite of insects.

Abstract: Wolbachia is an endosymbiont parasite that lives in the reproductive system 70% of all insects. It is passed down vertically to its offspring from the mother. Wolbachia occurs naturally in D. recens, but not D. subquinaria. In the wild, D. recens and D. subquinaria hybridize and about 2-3% of those hybrid offsprings contain a D. recenâ’s mitochondria, but not the wolbachia. This is a strange situation because the mitochondria is only passed down through the mother’s eggs, just like wolbachia. So how is it possible to have a D. recenâ’s mitochondria, but not the wolbachia as well? This peculiar scenario led to the question, is the transmission rate of wolbachia lower in hybrids compared to pure species? To answer this question, a D. recens female was crossed with a D. subquinaria. The F1 hybrid female was then backcrossed to a D. subquinaria male. The F1 and F2 generations were both test for wolbachia using PCR. The transmission rate for the F1 generation had a transmission rate of 100% and the F2 generation had a transmission rate of 95.7%. This shows that the transmission rate of wolbachia is lowered in hybrid species compared to pure species. Possible explanations for this decrease in transmission rate is because of the genetic variation between D. recens and D. subquinaria or the parasite could have been randomly loss due to oogenesis.


Download (PDF, 760KB)

Can Internal Parasites Affect Wound-healing Rates in Insects?

Lexi Calderon, a student from the University of Redlands, worked with Dr. Andy Davis and members of his lab to study parasites affect wound-healing in bess beetles.

Abstract: By definition, parasites depend on the resources of their host to survive. This relationship can result in a decrease of energy and fitness for the host. The parasitic nematode Chondronema passali resides in the hemocoel cavity of the bess beetle, Odontotaenius disjunctus. Although this parasite is non-lethal, a single beetle can harbor thousands of nematodes. Previous research has demonstrated this parasite affects the stress reaction of beetles, but very little research has investigated the effect parasites have on the host’s ability to heal a wound. Wound healing can be thought of as an indicator of the effectiveness of the immune system and by studying healing we can infer the effect this parasite has on the fitness of its host. We conducted a series of experiments where beetles were wounded with a dremel rotary drill and observed every hour for 12 hours after initial wounding. Each hour beetles were given a value from 1-5 to measure their status in the wound healing process, and values were summed to generate a ‘wound healing score’ for each beetle. Beetles were killed and dissected following the experiment to define gender and parasite abundance. Out of 188 beetles, 83% were infected with C.passali. Wound healing scores were not significantly predicted by parasite status. Beetle weight was a predictor of wound healing scores where heavier beetles had higher scores. Oxygen consumption was also measured in a subset of beetles after wounding, and we found parasitized beetles tended to have higher respiration (10% higher) than non-infected beetles.

Download (PDF, 1.39MB)


Microclimate effects on Aedes albopictus mosquitoes

Taylor McClanahan, a student at the University of Arkansas at Little Rock, worked with Dr. Courtney Murdock and members of her lab to examine how microclimate affects mosquitoes.

Abstract: Aedes albopictus, (Asian tiger mosquito), has successfully colonized in several countries in North and South America. Ae. albopictus is a highly efficient vector, capable of transmitting at least 27 different arboviruses, and is contributing to the global expansion of both dengue and Chikungunya. However, whether or not dengue or Chikungunya will emerge in a given area will depend on its interaction with local mosquito populations and local environmental conditions. The aim of this study was to characterize variation in local climate conditions and how this variation impacts Ae. albopictus traits important for transmission. An impervious surface map of Athens-Clarke County was used to select three urban, suburban, and rural sites (30m2). Six pots were placed (>10 m apart) at each site in full shade, filled with 200 ml leaf infusion, seeded with 30 Ae. albopictus larvae, and paired with a data logger on the inside and outside of the pot. All pots were checked daily for emerging adults, and any adults present were counted and removed. Urban sites were characterized by the following: warmer daily mean and minimum temperatures, decreased daily diurnal temperature variation, earlier adult emergence, and lower numbers of emerging adults relative to suburban and rural sites. Further, weather station temperature data were not necessarily a good predictor of mosquito microclimate across the three land uses. This cautions against the use of downscaled global climate patterns in predicting how vector-borne diseases may respond to current and future climate change. Ultimately, we see that microclimate data generates a more precise representation of the environments these mosquitoes inhabit.

Download (PDF, 1.55MB)


Behavioral determinants of parasite transmission in a monarch (Danaus plexippus) population

Anna Schneider, a student from the University of Wisconsin-Stevens Point, worked with mentors Dr. Sonia Altizer, Dr. Richard Hall, and Ania Majewska to look at how butterfly behavior affects parasite transmission.

Abstract: Altered behavior of an infected host can have important consequences for pathogen transmission. Pathogens can cause the host to increase foraging behavior and decrease activity levels due to increased energetic demands, which can significantly change the spread of the pathogen. Monarchs can suffer from a debilitating protozoan parasite, Ophryocystis elektroscirrha (OE), which is transmitted when infected adults inadvertently shed spores on milkweed (Asclepias spp.) leaves that are subsequently consumed by the caterpillars.  While infected adults are known to experience reduced flight ability and survival, less is known about how infection influences milkweed visitation behavior and, therefore, spore deposition.  Here, we investigated whether infection status altered activity budgets of wild adult Monarchs, particularly visitation rates to milkweed for foraging or oviposition.  Behavioral observations and milkweed visitation rates of adult Monarchs, both infected and uninfected, were collected in the butterfly gardens at the Wormsloe Historic Site in Savannah, GA.  Our results concluded that sex, not infection status, showed significance in variation of behavior.  Milkweed visitation rates were higher than previously thought and these are critical for parasite persistence.  These data provide the first field estimates of parasite spore deposition rates in monarchs.  We modified an existing differential equation model of monarch-OE dynamics to include adults contaminated with OE spores through mating and milkweed visitation.  According to this model, late-season OE prevalence varied between 16.5 and 78.6%.  This is consistent with the wide range of OE prevalence recorded in US monarchs (6-20% in the Midwest, up to 100% in tropical milkweed patches in the Southeast).

Download (PDF, 1.42MB)


Microbial Community Assessment of Lone Star Ticks from Athens, GA

Sydney Barosko, a student from Michigan State University, worked in the lab of Dr. Travis Glenn to examine pathogen diversity in local lone star ticks.

Abstract: In the world of infectious diseases, ticks play an important role as a vector in transmitting pathogens to humans, companion animals, livestock, and wildlife. Amblyomma americanum (Lone Star ticks) are known to transmit the pathogens that cause ehrlichiosis, babesiosis, Q fever, and rickettsial diseases. Few studies have been done on the pathogen diversity of Lone Star tick individuals. We used microbial 16S amplification followed by Illumina sequencing of the 16S amplicons to characterize microbial communities in A. americanum collected near Athens, GA. We examined differences in 16S sequences:  1) when two different Taq DNA polymerases were used for amplification (one with high fidelity and the other with more tolerance for low-quality samples and primer mismatches) and, 2) between 19 male and 18 female A. americanum ticks. We focused on three genera of microbes with known pathogenic strains:  Coxiella, Rickettsia, and Ehrlichia. We did not find any significant differences between the communities when amplified with the different Taq DNA polymerases nor in the infection rate of males vs. females infected with Ehrlichia or Rickettsia.  Male vs. female infection rates did, however, differ for Coxiella. The proportion of Coxiella in the microbiome was much higher in females than in males. Our work demonstrates that 16S microbiome sequencing can be an effective tool in characterizing pathogens in ticks and builds a foundation for larger-scale surveys in the future.


Download (PDF, 347KB)

Environmental and host factors affect bacterial community structure in the mosquito gut

Sofia Bertoloni Meli, a student from Indiana University, worked with Dr. Michael Strand and Kerri Coon to studied the microbial community found in the gut of mosquitoes.

Abstract: Insects host many essential microbial symbionts. The bacteria in mosquito guts are important for development, nutrient acquisition, and reproduction. Developing mosquito larvae acquire their gut bacterial community (microbiota) from the aquatic environment they live in. However, little is known about the factors influencing the abundance of specific community members in the larval gut. Here, we investigated the contribution of host factors in shaping mosquito gut microbiota. We used experimental studies to manipulate the community present in the environment of individual and cohabitating mosquito species. Quantitative analysis of community structure in mosquito larvae identified species-specific bacterial associations that were robust to changes in the environment. Overall, our results indicate that both environmental and host factors affect bacterial community structure in mosquitoes, and reveal the potential importance of incorporating host phylogenetic history into our understanding of gut microbial diversity.


Download (PDF, 196KB)

Microparasite challenge and subsequent energy trade-offs in an invasive crab species

Zain Aryanpour, a student at the University of Alabama, worked with Dr. Jeb Byers and Carrie Keogh to examine the cost of infection on immune response of an invasive crab species.

Abstract: Invasive species often show phenotypic distinctions in relation to their native-range species. A topic of current interest in populations of invasive species is their immune systems and functions, and whether costs of immune function are altered given the differences in selective pressures they experience in the invasive range. In our study, an invasive Asian shore crab species, Hemigrapsus sanguineus, was utilized as the model system for investigating the short-term energy demand in response to microparasite challenge, the potential relationship between supposed immune stimulation and bacterial killing ability, and the potential relationship between bacterial killing ability and respiration rate. For experimental variables, we utilized LPS injections as the microparasite challenge, optimized a bacterial killing assay to measure immune strength, and used a Qubit Respirometer to measure oxygen consumption for pre- and post-injection crabs. We then ran ANCOVA analyses on bacterial killing and oxygen consumption data and analyzed the relationships between data. The data suggests that microparasite challenge had no effect on energy expenditure in LPS crabs but PBS-injected control crabs showed significantly higher oxygen consumption than LPS crabs after injection. The challenge had little to no effect on bacterial killing ability on either experimental or control crabs. And finally, there is no significant relationship between bacterial killing ability and respiration rate. The results could either be explained by experimental errors in LPS injections (insufficient concentration of LPS, although 0.25 mg/mL was sufficient in previous studies) or the potential explanation that microparasite challenges are not costly on these crabs. A further comprehensive study with a combination of micro- and macroparasite challenges plus additional replicates would most likely give a clearer overview of the immune response and function in this wild population. Further experiments comparing native and invasive parasite response would also improve this study.

Download (PDF, 792KB)


Identifying Avian Haemosporidians in Turkey Vultures and Black Vultures from South Carolina

Alexandra Wickson, a student at the University of Georgia, worked with Dr. Michael Yabsley and others in his lab to determine parasite prevalence in vulture populations.

Abstract: Avian haemosporidian blood parasites are widespread among many families of birds and, in some species, can cause avian malaria.  In previous studies on blood parasites of vultures, prevalence and diversity of parasites were low. However, the long-term effects of infection on the birds were unknown. Overall, Turkey Vultures (Cathartes aura) have had a higher prevalence and diversity of blood parasites (i.e., Haemoproteus, Plasmodium, and Leucocytozoon spp.) compared with Black Vultures (Coragyps atratus) with only a single Plasmodium sp. infection has been reported in one Black Vulture from Florida. Based on morphological data, Haemoproteus catharti was described from the Turkey Vulture. The primary goal of this study was to better characterize H. catharti with morphologic and molecular data and to investigate ecological or intrinsic factors associated with infection. Turkey Vultures and Black Vultures were sampled at the Savannah River Site in Aiken, SC. Blood smears were immediately prepared, fixed with methanol, and stained with modified Giemsa. Parasite prevalence and parasitemia were determined by examination of at least 20,000 erythrocytes. We also conducted nested polymerase chain reaction (PCR) targeting the cytochrome b gene. We detected a high prevalence of parasites in Turkey Vultures (43%) and a complete absence of parasites in Black Vultures. No difference in prevalence or parasitemia levels were noted between sites, sexes, or age class. Phylogenetically, this parasite was most similar to a parasite reported from wood storks (Mycteria americana) from Florida. Together, these two sequences were distinct from the genera Haemoproteus and Plasmodium, and likely represent a new genus of avian blood parasite. This study documents the first genetic characterization of malarial parasites of vultures. Further genetic work targeting multiple genes is needed to confirm the phylogenetic relationship of this parasite to other avian haemosporidians.

Download (PDF, 581KB)


Baylisascaris procyonis prevalence and dynamics in a rodent population in Georgia

Ian Buchta, from Tulane University, worked with Dr. Michael Yabsley and members of his lab to study parasites in a local racoon population.

Ian Buchta1,2, Amanda Holley1, Kayla Buck1,3, Sarah Sapp1,4, Michael Yabsley1,3

Baylisascaris procyonis, the common roundworm parasite of raccoons, is a well-recognized zoonotic parasite. It utilizes small vertebrates as intermediate hosts and undergoes migration through the central nervous system which can lead to behavioral modifications or death. Previous studies on rodents have been conducted in Indiana where the prevalence of B. procyonis in raccoons is very high and only focused on a single species, the white-footed mouse (Peromyscus leucopus). In Georgia, the prevalence is low in raccoons, possibly due to its recent emergence. Our study was conducted to determine if rodents in Georgia are infected and investigate if other rodents are involved in the life cycle. Additionally, we tested if habitat disturbance impacted prevalence. Rodents were trapped at five sites with variable disturbance. After human euthanasia, brains were removed, pressed between glass slides, and microscopically analyzed for larvae. The remaining tissues, other than the skin, were digested in a 0.3% pepsin and 1% hydrochloric acid and the resulting liquid was analyzed for larvae. Infections were noted at two sites in Jackson and Clarke counties. Of 71 P. leucopus tested, seven (10%) were infected, although only one had larvae in the brain. None of the cotton rats (n=10), cotton mice (n=3), brown rats (n=4), or chipmunks (n=2) were infected. No difference in prevalence was noted for P. leucopus from sites with low or high levels of disturbance. Our finding of B. procyonis in P. leucopus is the first to document the parasite in a non-raccoon host in Georgia and of the parasite in Jackson Co., Georgia. Because this parasite causes disease in numerous avian and mammalian hosts, wildlife with neurologic disease should be considered suspects for B. procyonis infection



  1. Southeastern Cooperative Wildlife Disease Study, Department of Population Health, College of Veterinary Medicine,  Athens, GA 30602
  2. Tulane University, New Orleans, LA 70118
  3.  Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA 30602
  4. Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA 30602

Download (PDF, 1.06MB)

Spore persistence in the environment drives infection dynamics of a butterfly pathogen

Mary-Kate Williams, from the University of Arkansas at Little Rock, examined parasites of Monarch butterflies with Dr. Sonia Altizer, Dr. Richard Hall and graduate student Dara Satterfield.

Mary-Kate Williams1, Sonia Altizer2, Richard Hall2, Dara Satterfield2

1University of Arkansas at Little Rock, 2Odum School of Ecology, University of Georgia

Environmentally transmitted parasites commonly infect humans and wildlife. Environmental transmission is particularly important for insect pathogens, yet the factors affecting the persistence of infectious stages in the environment are poorly understood. Monarch butterflies are commonly infected by Ophryocystis elektroschirrha (OE); recent years have seen an increase in pathogen prevalence at the same time monarch populations in eastern North America have declined. OE is transmitted both vertically (from infected females to their progeny) and environmentally (when infected adults scatter spores onto milkweed leaves that are consumed by unrelated larvae). By using a combination of a mathematical modeling and an experimental study, we examined (1) how environmental conditions affect persistence of a free-living stage pathogen and (2) how pathogen shedding rate and environmental persistence time affect pathogen prevalence and host population size during the summer breeding season. We found that increased time spent fully exposed to environmental conditions (sun, rain, heat) reduced average infection severity induced by parasites, but did not reduce the fraction of monarchs infected by spores; therefore, parasites were able to remain viable after 15 days outdoors. Consistent with the experimental results, modeling findings showed that, parasite spores must persist for at least 20 days, in combination with a high shedding rate onto host plant leaves, for predicted prevalence to match the minimum prevalence observed in prior field studies.

Download (PDF, 1.19MB)

Development of deterministic and stochastic models for a T7 phage-E. coli system with vaccination strategy implementation

Abigail Smith, from Carnegie Mellon University, worked with Reni Kaul in the lab of Dr. John Drake to develop models to study the effectiveness of vaccination strategies.

Abigail L. Smith1, RajReni B. Kaul2 and John M. Drake2

1Carnegie Mellon University, 2Odum School of Ecology, University of Georgia

Vaccination is widely considered the most effective method of preventing the spread of infectious disease.  Pulse vaccination strategy, the repeated application of a vaccine over a defined population at a set time interval is gaining prominence as a strategy for the elimination of diseases such as measles, hepatitis, and smallpox. In order to study the effectiveness of this strategy, a bench experiment will be designed using E.coli bacteria and T7 bacteriophage, and studying the interactions and mechanisms in a chemostat. Using this system allows us to study the spread of infectious disease in laboratory setting. To test vaccination in system, a concentration of IPTG will be used to induce expression of the rcsA gene (immunity) in E. coli. Results can be generalized from an experimental bench system (E. coli bacteria and T7 phage) by developing a deterministic compartmental model, and then factoring in noise to form a stochastic model. Additional classes were added to track phage populations and experiment with vaccination strategy.  Preliminary studies were designed to study early warning signs for approaching a bifurcation point and critical slowing down, by examining the phage being driven to extinction.


Download (PDF, 683KB)


Photo credit: School of Life Sciences, Gibbet Hill Campus, The University of Warwick, Coventry, CV4 7AL