Dissertation
Host factors that alter Leishmania infantum transmission
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2018
DOI: 10.17077/etd.dw41vb22
Abstract
<p>Leishmaniasis is a parasitic disease that affects humans and animals in more than 98 countries across the globe placing more than 1 billion people at risk for the disease and killing more than 20,000 people per year. In the United States the disease is enzootic within the hunting dog population and vertical transmission has been identified as the primary route of transmission in this population. In Brazil the disease is endemic in the human population and enzootic in the dog population with vector and vertical transmission having been reported. In many diseases reports have found there is increased disease severity when an individual is co-infected with another organism. Case reports have suggested this may also occur with tick borne diseases and leishmaniosis in dogs but there is limited longitudinal data to support this relationship.</p>
<p>Even less is known and understood regarding the risk factors and basic reproduction number, number of secondary cases one infected individual can cause in a susceptible population, of leishmaniosis in regards to vertical transmission. The goal of the work presented in this thesis is to address host factors related to the transmission of L. infantum and the way in which co-infections affect the progression of the disease both in the U.S. and in Brazil. Understanding the risk factors associated with the transmission of the parasite Leishmania infantum, the causative agent of the disease, are necessary to controlling and potentially elimination the disease.</p>
<p>Utilizing a large prospective cohort and both active and passive surveillance it was identified that leishmaniosis can be maintained in a population via vertical transmission at prevalence rates similar to other endemic countries, 20%. With this knowledge an additional study examining a longitudinal cohort and assessing the impact of tick borne disease co-infections upon disease transmission was performed. It was identified that dogs exposed to three or more tick borne diseases were 11x more likely to progress to clinical disease (Adjusted RR: 11.64 95% CI: 1.22-110.99 p-value: 0.03) than dogs with no tick borne disease exposures. Furthermore, dogs with Leishmania and tick borne disease were 5x more likely to die within the study (RR: 4.85 95% CI: 1.65-14.24 p-value: 0.0051). When examining this relationship in a cross-sectional study in Brazil it was found that dogs with multiple tick borne disease exposures had 1.68x greater risk of being positive for Leishmania (Adjusted RR: 1.68 95% CI: 1.09-2.61 p-value: 0.019).</p>
<p>Using a retrospective cohort of dogs and information regarding their dam’s diagnostic status near the time of pregnancy risk factors associated with vertical transmission and the basic reproduction number were calculated. It was found that dogs who were born to dams that were ever diagnostically positive for exposure and/or infection with L. infantum were 13.84x more likely become positive for L. infantum within their lifetime (RR: 13.84 95% CI: 3.54-54.20 p-value < 0.0001). The basic reproduction number for vertically transmitted L. infantum within this cohort was 4.16.</p>
<p>The results of these studies suggest that leishmaniosis can be maintained in a population through vertical transmission. Furthermore, the studies show the risk factors associated with vertical transmission relate to the mother’s diagnostic status at time of pregnancy. The results of the co-infection studies highlight the importance of tick prevention in order to reduce disease progression. With increased disease severity associated with increased transmission to potential vectors these studies underline the need for immunotherapies and prevention measures to reduce disease progression in order to reduce transmission. Furthermore, these studies highlight the need for public health control and prevention programs to address vertical transmission if elimination of the disease is to ever be successful.</p>
Details
- Title: Subtitle
- Host factors that alter Leishmania infantum transmission
- Creators
- Angela Jean Toepp - University of Iowa
- Contributors
- Christine Petersen (Advisor)Mary E. Wilson (Committee Member)Jacob J. Oleson (Committee Member)James C. Torner (Committee Member)Marin L. Schweizer (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Epidemiology
- Date degree season
- Spring 2018
- DOI
- 10.17077/etd.dw41vb22
- Publisher
- University of Iowa
- Number of pages
- xiv, 152 pages
- Copyright
- Copyright © 2018 Angela Jean Toepp
- Language
- English
- Date submitted
- 08/29/2018
- Description illustrations
- color illustrations, maps
- Description bibliographic
- Includes bibliographical references.
- Public Abstract (ETD)
Leishmaniasis, caused by Leishmania parasites, is a deadly vector-borne protozoan disease endemic in more than 98 countries and 3 territories placing more than 1 billion people at risk. It affects over 1 million people each year and kills between 20,000 and 40,000 people annually. Leishmaniasis is a zoonotic disease, meaning it can be transmitted between animals and humans, leading to public health challenges for controlling or preventing disease. In the United States leishmaniasis is endemic within certain hunting dogs. Mom to pup, vertical transmission, is the main means of disease maintenance in this population. Understanding how leishmaniasis transmitted from mom to pup changes in prevalence and the ways in which co-infections affect the progression of disease has been the focus of this dissertation.
Using a hunting dog population several studies were performed in the United States and in Brazil to address these questions. The studies performed identified that leishmaniasis can be maintained within a population through vertical transmission, that co-infections can significantly increase the clinical progression of leishmaniasis, and that a mother’s diagnostic status is an important risk factors in predicting vertical transmission of the disease.
The results of these studies underline the need for risk management and control efforts to address vertical transmission. Furthermore, these studies show that any efforts to eliminate leishmaniasis need to address the potential impact of vertical transmission.
- Academic Unit
- Epidemiology
- Record Identifier
- 9983777170602771
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