Associations between biotic and abiotic factors and Chagas disease vector abundance in palm trees across different habitat types

Jason Soriano, a freshman from University of California Berkeley, worked with Dr. Nicole Gottdenker and Christina Varian to investigate the factors influencing the abundance of an important disease vector.

Abstract:  In the Americas, an estimated 8 million people are infected with Chagas disease, a tropical, vector-borne infectious disease that can be life threatening if not properly treated. It is caused by the protozoan Trypanosoma cruzi which is transmitted by triatomine insect vectors called Rhodnius pallescens , reduviid bugs that are more commonly referred to as “kissing bugs” for their characteristic bites proximal to the lips and eyelids of humans. In Panama, sylvatic transmission of T. cruzi commonly occurs in the crown of the Attalea butyracea palm, the region of the palm tree where kissing bugs live. However, transmission can often spillover into human populations when infected vectors come into contact with humans. Previous studies have proven that land use change (e.g. deforestation) increase R. pallescens abundance, but the underlying mechanisms as to why this pattern occurs are largely unknown. Therefore, this research serves to shed some light on potential biotic and abiotic factors associated with vector abundance in A. butyracea palm trees across different habitat types. Through data visualization and statistical analysis of field data collected from four sites in central Panama, we show that microenvironment factors (primarily dead organic matter, relative humidity, and number of connected trees) are significantly correlated with R. pallescens abundance. Evaluating mechanisms as potential targets of palm management strategies aiming to control R. pallescens abundance will ultimately minimize disease risk and uphold the health, safety, and welfare of vulnerable communities.

Download (PDF, 4.69MB)

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)


Kissing Bug (R. pallescens) Population Structure in Panamanian Rural Landscapes

Anaija Hardmon, a Biology major from Spelman College, worked in the lab of Dr. Nicole Gottdenker to describe the population structure of an important disease vector.

Abstract: Describing the population structure of zoonotic disease vectors includes understanding their life history strategies and population dynamics, as well as the development of vector-borne diseases, and control strategies for the Chagas disease. This disease is caused by the protozoan parasite Trypanosoma cruzi and transmitted by hematophagous members of the familyTriatominae to humans and mammals alike.  The objective of this study was to describe and compare the population structure of the principal vector of Chagas disease in Panama, R. pallescens, across different types of anthropogenic land use. We evaluated the population structure of N= 1123 bugs in total, collected from 5 different habitat types in Panama during the wet seasons of 2008 with N= 759 collected and between 2013-2015 in forest patch, pasture, and peridomestic habitats. There was a significant association between bug stage and habitat type (Chi-squared = 37.3, df = 20, p =0.02). The N1 and N2 nymphs were under-represented in the sample, and the estimated numbers of N3, N4, and N5 stage nymphs were significantly greater in disturbed habitats, with N5 stages being particularly scarce in contiguous forest and cattle pasture where the lowest number of bugs were collected. Nymph: Adult ratios did not significantly differ between habitat types, but tended to be higher in pasture sites. In bugs captured between 2013-2015, more bugs were captured in the Trinidad de las Minas site compared to Las Pavas and there were no apparent inter-annual trends in age structure in these sites. Once errors in detectability are accounted for, this data can be used for the analysis of bug population dynamics within and between habitats.

Download (PDF, 671KB)


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)


Identifying Chagas Disease Reservoirs with PCR and Next-generation DNA Sequencing

For this project, students Nicolas Means from Oklahoma State University and Darlisha Owens from Grambling State University, teamed up with Dr. Travis Glenn in the Department of Environmental Health Science and Dr. Nicole Gottdenker in Veterinary Medicine to use next-generation DNA sequencing to identify disease reservoirs.

Nicolas J. Means1, Darlisha Owens2, Troy Kieran3, Travis C. Glenn3, Nicole Gottdenker3

1Oklahoma State University, 2 Grambling State University

3University of Georiga

American trypanosomiasis (Chagas Disease) is a zoonotic vector-borne disease caused by the protozoan parasite Trypanosoma cruzi,  and is an important cause of morbidity and mortality in Latin America. T. cruzi circulates between reservoir hosts (wild and domestic mammals) and hematophagous triatomine insect vectors. Humans are susceptible to the disease once infected with the parasite by contact with the infected insect vector, ingestion of food or drink contaminated with the pathogen, transplacental transmission, or by transfusion with infected blood or tissue transplants. Research has shown that blood meal analysis, via standard PCR and sequencing, are capable of identifying host reservoirs down to the species level, but these techniques are limited because: 1) they often cannot identify multiple blood meals within a vector, 2) they cannot be used to simultaneously detect vector infection with trypanosomes or coinfection with other pathogens, and 3) they may require a relatively large amount of vertebrate reservoir DNA, which may be degraded in the insect vector. The objective of this study is to standardize next generation sequence methodologies for simultaneous blood meal species identification and trypanosome infection within kissing bugs, Rhodnius pallescens, a triatomine vector of Chagas disease.

To prepare samples for next generation sequencing, we had to quantify the amount of DNA extracted from R. pallescens, normalize the DNA concentrations, and optimize the PCR conditions for each portion of the next generation Taggimatrix technique.  The samples were put in three different groups consisting of high, medium, and low concentration DNA.  For optimization of the PCR, there were a series of tests with a known insect and vertebrate. Conditions such as number of cycles, temperature and time changed throughout each experiment. We then used the optimized PCR conditions on the DNA from the three groups (high, medium and low) to obtain amplification of vertebrate and trypanosome DNA. From the tests, we found that 30% of the new samples that were collected had the trypanosome parasite within the DNA of the insect while 68% showed vertebrate DNA within the blood meal.

Download (PDF, 703KB)

Modeling Chagas disease vector infection prevalence: incorporating life history characteristics and community composition

Authors: Carolina Cabrera, Nicole L. Gottdenker

Abstract Multihost vector-borne pathogens play an important role in human and veterinary public health worldwide, and understanding factors that drive their transmission is critical to the development of vector-borne disease prevention and control. Two potentially important drivers of multihost vector-born pathogen transmission are 1) the community composition of reservoir host species that come in contact with the vector in a particular habitat, and 2) the life history characteristics of reservoir hosts. One of the most important multihost vector-borne pathogens in the Americas, infecting over 10 million people, is the protozoan parasite Trypanosoma cruzi, the cause of Chagas disease in humans. T. cruzi circulates between wild and domestic animal reservoirs and humans, and is transmitted by a triatomine vector. The objective of this study is to develop a mathematical model that attempts to incorporate biological realities of Trypanosoma cruzi transmission between reservoir hosts and a triatomine vector. Specifically, we evaluate the Chagas disease system in Panama, consisting of a wide range of mammalian reservoir hosts and the main vector Rhodnius pallescens. We link a deterministic SI model for pathogen transmission in the vector with an SI model that describes host community transmission, incorporating host community structure and host life history characteristics, as well as hosts that have been previously infected with T. cruzi, but have developed partial immunity and are less competent reservoirs. Using field and molecular blood meal data, and values from the literature, we calculate a reservoir potential index for the different habitats within this Chagas disease system and evaluate the degree to which changes in reservoir community structure and life history characteristics impact vector infection prevalence.

Download (PDF, 483KB)