Parasitology Commons^™

Concepts In Animal Parasitology, Chapter 51: Heterakoidea (Superfamily): Cosmopolitan Gut-Dwelling Parasites Of Tetrapods [Nemata, Secernentea], F. Agustín Jiménez-Ruiz

Concepts in Animal Parasitology

An overview of the cosmopolitan gut-dwelling nematodes (roundworms) in the superfamily Heterakoidea, which occur most often in the cecum and large intestine of amphibians, reptiles, birds, and mammals. Discusses the general morphological characteristics, diagnosis, distribution and host associations, general biology, evolution, systematics, phylogeny, ecology, and conservation, including coverage of species of veterinary importance, Heterakis gallinarum and Histomonas meleagridis.

Chapter 51 in Concepts in Animal Parasitology, by F. Agustín Jiménez-Ruiz. 2024. S. L. Gardner and S. A. Gardner, editors. Zea Books, Lincoln, Nebraska, United States. doi: 10.32873/unl.dc.ciap051

Concepts In Animal Parasitology, Chapter 57: Nematomorpha (Phylum): Horsehair Worms, Matthew G. Bolek, Ben Hanelt

Concepts in Animal Parasitology

An overview of the horsehair worms, phylum Nematomorpha, including discussion of their general morphology, life cycle, distribution, diversity, taxonomy, phylogeny, ecology, and behavior.

Chapter 57 in Concepts in Animal Parasitology, by Matthew G. Bolek and Ben Hanelt. 2024. S. L. Gardner and S. A. Gardner, editors. Zea Books, Lincoln, Nebraska, United States. doi: 10.32873/unl.dc.ciap057

Concepts In Animal Parasitology, Chapter 09: The Coccidia Proper: Important Apicomplexa Other Than Haemoprotozoa [Protozoa, Apicomplexa], Donald W. Duszynski

Concepts in Animal Parasitology

Chapter 9 in Concepts in Animal Parasitology on the Coccidia Ppoper, important Apicomplexa other than Haemoprotozoa by Donald W. Duszynski. 2024. S. L. Gardner and S. A. Gardner, editors. Zea Books, Lincoln, Nebraska, United States. doi: 10.32873/unl.dc.ciap009

Human-Bat Interactions In A Disease Emergence Hotspot: Implications For Human Health And Bat Conservation, Reilly Tempest Jackson

Graduate Theses and Dissertations

Bats are an ecologically important taxon that can host zoonotic pathogens. Globally, many bat species are synanthropic and live closely with humans, often roosting in man-made structures. The spatial overlap between humans and bats creates opportunities for human-bat contact, which can lead to human exposure to bat-borne pathogens and conflicts that cause bat mortality. Despite this risk, little is known about the drivers and characteristics of these human-bat interactions in buildings and work is needed to understand this aspect of the wildlife-urban interface. In Chapter I, I present a literature review that identifies the geographic and taxonomic trends in reported …

Leucocytozoon Cariamae N. Sp. And Haemoproteus Pulcher Coinfection In Cariama Cristata (Aves: Cariamiformes): First Mitochondrial Genome Analysis And Morphological Description Of A Leucocytozoid In Brazil, Lis Marques De C. Vieira, Pedro Henrique O. Pereira, Daniel Ambrózio Da Rocha Vilela, Irène Landau, M. Andreína Pacheco, Ananias A. Escalante, Francisco C. Ferreira, Érika Martins Braga

Harold W. Manter Laboratory of Parasitology: Library Materials

The distribution of avian haemosporidians of the genus Leucocytozoon in the Neotropics remains poorly understood. Recent studies confirmed their presence in the region using molecular techniques alone, but evidence for gametocytes and data on putative competent hosts for Leucocytozoon are still lacking outside highland areas. We combined morphological and molecular data to characterize a new Leucocytozoon species infecting a non-migratory red-legged seriema (Cariama cristata), the first report of a competent host for Leucocytozoon in Brazil. Leucocytozoon cariamae n. sp. is distinguished from the Leucocytozoon fringillinarum group by its microgametocytes that are not strongly appressed to the host cell …

Newer Surveillance Data Extends Our Understanding Of The Niche Of Rickettsia Montanensis (Rickettsiales: Rickettsiaceae) Infection Of The American Dog Tick (Acari: Ixodidae) In The United States, Catherine A. Lippi, Holly D. Gaff, Robyn M. Nadolny, Sadie J. Ryan

Biological Sciences Faculty Publications

Background: Understanding the geographic distribution of Rickettsia montanensis infections in Dermacentor variabilis is important for tick-borne disease management in the United States, as both a tick-borne agent of interest and a potential confounder in surveillance of other rickettsial diseases. Two previous studies modeled niche suitability for D. variabilis with and without R. montanensis, from 2002-2012, indicating that the D. variabilis niche overestimates the infected niche. This study updates these, adding data since 2012.

Methods: Newer surveillance and testing data were used to update Species Distribution Models (SDMs) of D. variabilis, and R. montanensis infected D. variabilis, in …

Prevalence Of Ehrlichia And Rickettsia Within Ticks In Arkansas State Parks, Haley Stanton

Animal Science Undergraduate Honors Theses

Within the past few decades, the number of diagnoses of tick-borne diseases – such as spotted fever rickettsiosis and ehrlichiosis – has steadily increased throughout the United States, with Arkansas having one of the highest rates in the country. These diseases pose a risk to both humans and animals, as both can acquire these infections from ticks. Due to the increasing geographic range of ticks, rise in cases, and likely underdiagnosis of these diseases, this study aimed to identify the infection rate of ticks themselves in multiple state parks in Arkansas. Four Arkansas state parks were each visited once a …

Investigating Novel Chemotherapeutics Against The Parasite Toxoplasma Gondii, Braydon Dreher

Theses/Capstones/Creative Projects

Toxoplasma gondii, an intracellular protozoan, is a globally prevalent parasite due to the infectivity of T. gondii with nearly 2.5 billion people affected worldwide. Toxoplasma gondii can cause toxoplasmosis, which is a disease acquired through the consumption of undercooked meat or found in the feces of felines, and often leads to profound neuropathology and potentially death. Currently, acute toxoplasmosis is treated with pyrimethamine and sulfadiazine, which is a combination of an antiprotozoal and a sulfonamide. This combination of drugs directly targets the acute stage of infection but has failed to eliminate or impact the chronic carriage of bradyzoites while …

Prevalence Of Dog Heartworm (Dirofilaria Immitis) Infection In Invasive Aedes Aegypti And Aedes Albopictus Mosquitoes In Southern California, Irene Hui Ying Lee, Donghwi Kim, Romina Lee

Pacific Undergraduate Research and Creativity Conference (PURCC)

No abstract provided.

Multipatch Stochastic Epidemic Model For The Dynamics Of A Tick-Borne Disease, Milliward Maliyoni, Holly D. Gaff, Keshlan S. Govinder, Faraimunashe Chirove

Biological Sciences Faculty Publications

Spatial heterogeneity and migration of hosts and ticks have an impact on the spread, extinction and persistence of tick-borne diseases. In this paper, we investigate the impact of between-patch migration of white-tailed deer and lone star ticks on the dynamics of a tick-borne disease with regard to disease extinction and persistence using a system of Itô stochastic differential equations model. It is shown that the disease-free equilibrium exists and is unique. The general formula for computing the basic reproduction number for all patches is derived. We show that for patches in isolation, the basic reproduction number is equal to the …

Exploring The Evolution Of Trypanosoma Cruzi And The Emergence Of Chagas Disease In The Context Of Environmental Change: Applying The Stockholm Paradigm To Archaeoparasitology, Part I, Aida Romera Barbera, Daniel R. Brooks, T. Michael Fink, Karl J. Reinhard

Karl Reinhard Publications

The Stockholm Paradigm is an evolutionary synthesis that explains the emergence of novel pathogens in the context of environmental disturbances. Considering the urgent climate change situation, anticipation stands as key to prevent and mitigate the effects that climate change can have in the emergence of pathogens. However, the success of preventive measures is hindered by a limited knowledge of the interplaying dynamics between biology, environment, and culture leading to emerging infectious diseases. For many decades, bioarchaeologists have been gathering data on past human-environment interactions, therefore contributing to the conversation. Archaeoparasitology, at the intersection between pathology, bioarchaeology, and biology, is uniquely …

Documenting The Presence Of Chagas Disease In Prehistoric North America: Applying The Stockholm Paradigm To Archaeoparasitology, Part Ii, Karl J. Reinhard, Daniel R. Brooks, Aida Romera Barbera, T. Michael Fink

Karl Reinhard Publications

The DAMA protocol (Document, Assess, Monitor, Act) is the applied aspect of the Stockholm Paradigm. Evidence from archaeology and history of medicine has a demonstrated value in documenting infection risk for specific study areas. Bioarchaeological remains and historical documents show vivid examples of pathology related to the Chagas disease life cycle. The science of archaeology defines the lifestyles that created risk of triatomine kissing bug infestations and trypanosome protozoa infections. Paleogenetics, in the form of molecular analyses of Trypanosoma cruzi, elucidate the temporal origins of genetic variants and adaptation to human environments. We illustrate how these fields reveal the risk …

Anthelmintic Resistance In Sheep Across Ireland And The Uk: A Literature Review Of The In Vivo Versus In Vitro Methods, Megan Tumulty

SURE Journal: Science Undergraduate Research Experience Journal

Background: The animal welfare and production consequences of gastrointestinal nematode infections, namely Nematodirus battus, on sheep are compelling. The control of gastrointestinal infections has been heavily reliant on the administration of anthelmintics since their introduction into mainstream use in 1960. However, their frequent and often excessive use has resulted in anthelmintic resistance being reported extensively in several gastrointestinal nematode species. The prevalence of anthelmintic resistance as well as the increase in the number of cases of multiple-drug resistance in nematode populations now poses substantial hindrance on the viability of sheep production systems. However, despite the threat N. battus poses …

Infection And Transmission Determinants Of Flea-Borne Rickettsioses, Hanna J. Laukaitis

Graduate Theses and Dissertations (2019 - present)

The genus Rickettsia is comprised of Gram-negative, obligate intracellular bacteria that are spread by hematophagous arthropods. Elucidating the factors conferring rickettsial virulence has perplexed investigators for decades, complicated by the lack of efficient genetic tools necessary to uncover rickettsial- and vector-specific factors contributing to persistence. The advent of transposon mutagenesis has enabled the field to make vast developments in uncovering novel rickettsial mechanisms utilized in various host backgrounds. Thus, the aim of this study was to generate Rickettsia felis transposon mutants and characterize novel phenotypes associated with genetic disruption in an arthropod background. Distribution of rickettsiae is reliant on the …

Stepping-Stones And Mediators Of Pandemic Expansion: A Context For Humans As Ecological Super-Spreaders, Eric P. Hoberg, Walter A. Boeger, Daniel R. Brooks, Valeria Trivellone, Salvatore J. Agosta

MANTER: Journal of Parasite Biodiversity

Humans represent ecological super-spreaders in the dissemination and introduction of pathogens. These processes, consistent with the dynamics of the Stockholm paradigm, are exemplified in the origin and globalized distributions of SARS-CoV-2 since initial recognition in central Asia during 2019 and 2020. SARS-like viruses are not widespread in mammals but appear widespread in chiropterans. Bats are isolated ecologically from most other assemblages of mammals in terrestrial systems. Humans may be the stepping-stone hosts for broad global dissemination and wider infection (given the opportunity) among diverse assemblages of mammals in which host and viral capacity are compatible. Human globalization mediated insertion in …

Larval Habitats, Species Composition And Distribution Of Malaria Vectors In Regions With Autochthonous And Imported Malaria In Roraima State, Brazil, Nathália Coelho Vargas De Almeida, Jaime Louzada, Maycon Sebastião Alberto Santos Neves, Thiago M. Carvalho, Júlio Castro‑Alves, Teresa Fernandes Silva‑Do‑Nascimento, Ananias A. Escalante, Joseli Oliveira‑Ferreira

Harold W. Manter Laboratory of Parasitology: Library Materials

Background: Malaria control requires local action. Assessing the vector diversity and abundance provides information on the local malariogenic potential or risk of transmission. This study aimed to determine the Anopheles species composition, habitats, seasonal occurrence, and distribution in areas with autochthonous and imported malaria cases in Roraima State.

Methods: A longitudinal study was conducted from January 2017 to October 2018, sampling larvae and adult mosquitoes in three municipalities of Roraima State: Boa Vista, Pacaraima and São João da Baliza. These areas have different risks of malaria importation. Four to six mosquito larval habitats were selected for larval sampling …

Comparison Of Percutaneous Vs Oral Infection Of Hamsters With The Hookworm Ancylostoma Ceylanicum: Parasite Development, Pathology And Primary Immune Response, Richard D. Bungiro, Lisa M. Harrison, Blaise Dondji, Michael Cappello

Biology Faculty Scholarship

Background

Hundreds of millions of people in poor countries continue to suffer from disease caused by bloodfeeding hookworms. While mice and rats are not reliably permissive hosts for any human hookworm species, adult Golden Syrian hamsters are fully permissive for the human and animal pathogen Ancylostoma ceylanicum. Similar to humans, hamsters may be infected with A. ceylanicum third-stage larvae orally or percutaneously. Oral infection typically leads to consistent worm yields in hamsters but may not accurately reflect the clinical and immunological manifestations of human infection resulting from skin penetration.

Methodology/Principal findings

In this study we compared host responses …

Rickettsial Pathogen Perturbs Tick Circadian Gene To Infect The Vertebrate Host, Supreet Khanal, Vikas Taank, John F. Anderson, Hameeda Sultana, Girish Neelakanta

Biological Sciences Faculty Publications

Ixodes scapularis is a medically important tick that transmits several microbes to humans, including rickettsial pathogen Anaplasma phagocytophilum. In nature, these ticks encounter several abiotic factors including changes in temperature, humidity, and light. Many organisms use endogenously generated circadian pathways to encounter abiotic factors. In this study, we provide evidence for the first time to show that A. phagocytophilum modulates the arthropod circadian gene for its transmission to the vertebrate host. We noted a circadian oscillation in the expression of arthropod clock, bmal1, period and timeless genes when ticks or tick cells were exposed to alternate 12 h …

Malaria Resilience In South America: Epidemiology, Vector Biology, And Immunology Insights From The Amazonian International Center Of Excellence In Malaria Research Network In Peru And Brazil, Kathrine Torres, Marcelo U. Ferreira, Marcia C. Castro, Ananias A. Escalante, Jan E. Conn, Elizabeth Villasis, Maisa Da Silva Araujo, Gregorio Almeida, Priscila T. Rodrigues, Rodrigo M. Corder, Anderson R.J. Fernandes, Priscila R. Calil, Winni A. Ladeia, Stefano S. Garcia-Castillo, Joaquin Gomez, Lis Ribeiro Do Valle Antonelli, Ricardo T. Gazzinelli, Douglas T. Golenbock, Alejandro Llanos-Cuentas, Dionicia Gamboa, Joseph M. Vinetz

Harold W. Manter Laboratory of Parasitology: Library Materials

The 1990s saw the rapid reemergence of malaria in Amazonia, where it remains an important public health priority in South America. The Amazonian International Center of Excellence in Malaria Research (ICEMR) was designed to take a multidisciplinary approach toward identifying novel malaria control and elimination strategies. Based on geographically and epidemiologically distinct sites in the Northeastern Peruvian and Western Brazilian Amazon regions, synergistic projects integrate malaria epidemiology, vector biology, and immunology. The Amazonian ICEMR’s overarching goal is to understand how human behavior and other sociodemographic features of human reservoirs of transmission— predominantly asymptomatically parasitemic people—interact with the major Amazonian malaria …

Genomic Approaches To Uncovering The Coevolutionary History Of Parasitic Lice [Review], Kevin P. Johnson

Harold W. Manter Laboratory of Parasitology: Library Materials

Next-generation sequencing technologies are revolutionizing the fields of genomics, phylogenetics, and population genetics. These new genomic approaches have been extensively applied to a major group of parasites, the lice (Insecta: Phthiraptera) of birds and mammals. Two louse genomes have been assembled and annotated to date, and these have opened up new resources for the study of louse biology. Whole genome sequencing has been used to assemble large phylogenomic datasets for lice, incorporating sequences of thousands of genes. These datasets have provided highly supported trees at all taxonomic levels, ranging from relationships among the major groups of lice to those among …

Investigation Of Histomoniasis Prevention In Poultry, Lesleigh Beer

Graduate Theses and Dissertations

Histomonas meleagridis is the etiological agent of histomoniasis, also commonly known as blackhead disease. This protozoal disease of poultry is detrimental to turkeys with flock mortalities often reaching 80-100%, although other gallinaceous birds are susceptible. Since the voluntary removal of nitarsone in 2015, the poultry industry is suffering with no approved prophylactics, therapeutics, or vaccines for this disease. The objectives of this dissertation were to evaluate multiple methods for prevention or control of histomoniasis, including dietary chemoprophylaxis and vaccination. Specifically, this research evaluated quinine as a chemoprophylactic candidate (Chapter 3) or live-attenuated H. meleagridis as vaccine candidates (Chapter 4) in …

Complexity Of Malaria Transmission Dynamics In The Brazilian Atlantic Forest, Ana Maria Ribeiro De Castro Duarte, Licia Natal Fernandes, Fabiana Santos Silva, Igor Lucoves Sicchi, Luis Filipe Mucci, Izilda Curado, Aristides Ferrnandes, Antônio Ralph Medeiros-Sousa, Walter Ceretti-Junior, Mauro Toledo Marrelli, Eduardo Evangelista, Renildo Teixeira, Juliana Laurito Summa, Marcello Schiavo Nardi, Margoth Ramos Garnica, Ana Carolina Loss, Julyana Cerqueira Buery, Crispim Cerutti Jr., M. Andreína Pacheco, Ananias A. Escalante, Maria Anice Mureb Sallum, Gabriel Zorello Laporta

Harold W. Manter Laboratory of Parasitology: Library Materials

Plasmodium malariae and Plasmodium vivax are protozoan parasites that can cause malaria in humans. They are genetically indistinguishable from, respectively, Plasmodium brasilianum and Plasmodium simium, that is, parasites infecting New World non-human primates in South America. In the tropical rainforests of the Brazilian Atlantic coast, it has long been hypothesized that P. brasilianum and P. simium in platyrrhine primates originated from P. malariae and P. vivax in humans. A recent hypothesis proposed the inclusion of Plasmodium falciparum into the transmission dynamics between humans and non-human primates in the Brazilian Atlantic tropical rainforest. Herein, we assess the occurrence of human …

Malaria In Southern Venezuela: The Hottest Hotspot In Latin America, Maria Eugenia Grillet, Jorge E. Moreno, Juan V. Hernández-Villena, Maria F. Vincenti-González, Oscar Noya, Adriana Tami, Alberto Paniz-Mondolfi, Martin Llewellyn, Rachel Lowe, Ananias A. Escalante, Jan E. Conn

Harold W. Manter Laboratory of Parasitology: Library Materials

Malaria elimination in Latin America is becoming an elusive goal. Malaria cases reached a historical ~1 million in 2017 and 2018, with Venezuela contributing 53% and 51% of those cases, respectively. Historically, malaria incidence in southern Venezuela has accounted for most of the country’s total number of cases. The efficient deployment of disease prevention measures and prediction of disease spread to new regions requires an in-depth understanding of spatial heterogeneity on malaria transmission dynamics. Herein, we characterized the spatial epidemiology of malaria in southern Venezuela from 2007 through 2017 and described the extent to which malaria distribution has changed country-wide …

Dirofilaria Immitis Prevalence In Canis Latrans In Kentucky, Melanie Ann Brandon

Murray State Theses and Dissertations

Dirofilaria immitis (canine heartworm) was found in forty-two (42) of the two hundred seventy-five (275) Canis latrans (coyote) necropsied in the state of Kentucky from November 27, 2019 through March 3, 2021. Thirty-five (35) of the positive cases were from western Kentucky region with the other seven spread across the state. With this group of coyotes, one hundred fifty-eight (158) were male and the other one hundred six-teen (116) were female. The estimated age ranged from a pup to senior dogs. A little over forty percent of the dogs were obtained through coyote/predator tournaments; the remaining were acquired from pest …

Occurrence Of Pulmonary Arteritis With Lungworm Infections In Gray Seals From New England, 2013-2020, Jillian R. Broadhurst, Inga Sidor Dvm, Ms, Dacvp

Honors Theses and Capstones

Gray seals (Halichoerus grypus) are a common pinniped species in New England coastal waters. Parasitic infection is an important cause of mortality for this species, and lungworm species are frequently implicated in cases of respiratory infection, especially in pups and weanling seals. The most common of these is Otostrongylus circumlitus, a large nematode found in the bronchi and bronchioles of affected seals. The full life cycle is unknown but its presence in lungs and sometimes pulmonary arteries suggests that migration via arterial circulation occurs. Signs and microscopic findings are widely variable; our cases included dyspnea, bloody mucoid …

Microbiomes Of Blood-Feeding Arthropods: Genes Coding For Essential Nutrients And Relation To Vector Fitness And Pathogenic Infections. A Review, Daniel E. Sonenshine, Philip E. Stewart

Biological Sciences Faculty Publications

Blood-feeding arthropods support a diverse array of symbiotic microbes, some of which facilitate host growth and development whereas others are detrimental to vector-borne pathogens. We found a common core constituency among the microbiota of 16 different arthropod blood-sucking disease vectors, including Bacillaceae, Rickettsiaceae, Anaplasmataceae, Sphingomonadaceae, Enterobacteriaceae, Pseudomonadaceae, Moraxellaceae and Staphylococcaceae. By comparing 21 genomes of common bacterial symbionts in blood-feeding vectors versus non-blooding insects, we found that certain enteric bacteria benefit their hosts by upregulating numerous genes coding for essential nutrients. Bacteria of blood-sucking vectors expressed significantly more genes (p < 0.001) coding for these essential nutrients than those of non-blooding insects. Moreover, compared to endosymbionts, the genomes of enteric bacteria also contained significantly more genes (p < 0.001) that code for the synthesis of essential amino acids and proteins that detoxify reactive oxygen species. In contrast, microbes in non-blood-feeding insects expressed few gene families coding for these nutrient categories. We also discuss specific midgut bacteria essential for the normal development of pathogens (e.g., Leishmania) versus …

Trends And Opportunities In Tick-Borne Disease Geography, Catherine A. Lippi, Sadie J. Ryan, Alexis L. White, Holly D. Gaff, Colin J. Carlson

Biological Sciences Faculty Publications

Tick-borne diseases are a growing problem in many parts of the world, and their surveillance and control touch on challenging issues in medical entomology, agricultural health, veterinary medicine, and biosecurity. Spatial approaches can be used to synthesize the data generated by integrative One Health surveillance systems, and help stakeholders, managers, and medical geographers understand the current and future distribution of risk. Here, we performed a systematic review of over 8,000 studies and identified a total of 303 scientific publications that map tick-borne diseases using data on vectors, pathogens, and hosts (including wildlife, livestock, and human cases). We find that the …

Tetraspanins As Potential Therapeutic Candidates For Targeting Flaviviruses, Waqas Ahmed, Girish Neelakanta, Hameeda Sultana

Biological Sciences Faculty Publications

Tetraspanin family of proteins participates in numerous fundamental signaling pathways involved in viral transmission, virus-specific immunity, and virus-mediated vesicular trafficking. Studies in the identification of novel therapeutic candidates and strategies to target West Nile virus, dengue and Zika viruses are highly warranted due to the failure in development of vaccines. Recent evidences have shown that the widely distributed tetraspanin proteins may provide a platform for the development of novel therapeutic approaches. In this review, we discuss the diversified and important functions of tetraspanins in exosome/extracellular vesicle biology, virus-host interactions, virus-mediated vesicular trafficking, modulation of immune mechanism(s), and their possible role(s) …

Complete Genome Sequence Of Rickettsia Parkeri Strain Black Gap, Sandor E. Karpathy, Christopher D. Paddock, Stephanie L. Grizzard, Dhwani Batra, Lori A. Rowe, David T. Gauthier

Biological Sciences Faculty Publications

A unique genotype of Rickettsia parkeri, designated R. parkeri strain Black Gap, has thus far been associated exclusively with the North American tick, Dermacentor parumapertus. The compete genome consists of a single circular chromosome with 1,329,522 bp and a G+C content of 32.5%.

Tick Ecdysteroid Hormone, Global Microbiota/Rickettsia Signaling In The Ovary Versus Carcass During Vitellogenesis In Part-Fed (Virgin) American Dog Ticks, Dermacentor Variabilis, Loganathan Ponnusamy, Haley Sutton, Robert D. Mitchell Iii, Daniel E. Sonenshine, Charles S. Apperson, Richard Michael Roe

Biological Sciences Faculty Publications

The transovarial transmission of tick-borne bacterial pathogens is an important mechanism for their maintenance in natural populations and transmission, causing disease in humans and animals. The mechanism for this transmission and the possible role of tick hormones facilitating this process have never been studied. Injections of physiological levels of the tick hormone, 20-hydroxyecdysone (20E), into part-fed (virgin) adult females of the American dog tick, Dermacentor variabilis, attached to the host caused a reduction in density of Rickettsia montanensis in the carcass and an increase in the ovaries compared to buffer-injected controls. This injection initiates yolk protein synthesis and uptake …