Recipient Organization
UNIVERSITY OF FLORIDA
G022 MCCARTY HALL
GAINESVILLE,FL 32611
Performing Department
College of Veterinary Medicine
Non Technical Summary
It is important to keep foreign animal diseases out of the U.S. One disease carried by ticks and present on several Caribbean islands is known as "heartwater". This disease causes high mortalities in sheep, goats and cattle. There is an infectious agent already present in the U.S. known as the Panola Mountain Ehrlichia or PME (because of its discovery in Panola Mountain State Park, Georgia), which is closely related to the organism causing heartwater disease. PME causes a much less severe disease than the agent of heartwater but the two infections can be confused using current diagnostic assays. We propose to isolate and characterize PME and develop better assays to distinguish these two organisms.
Animal Health Component
30%
Research Effort Categories
Basic
70%
Applied
30%
Developmental
(N/A)
Goals / Objectives
Ehrlichia ruminantium is a Gram-negative rickettsia that is the agent of heartwater disease in Africa and the Caribbean. Heartwater disease causes high mortalities in sheep, goats and cattle. There is a risk of introduction of the disease into the U.S. via infected ticks carried on imported animals or birds or in infected carrier animals. Once introduced, the disease would be difficult to eliminate because the organism can infect native U.S. species of Amblyomma ticks and wild ruminants. Both the ticks and wild ruminants could act as reservoirs for further infection of domestic livestock, with devastating economic consequences. Recently, a novel tick-borne ehrlichial agent has been identified in U.S. ticks which is closely related to the agent of heartwater disease. The agent is known as the Panola Mountain Ehrlichia or PME agent because it was first identified in adult Amblyomma americanum ticks collected from the Panola Mountain State Park, near Atlanta, Georgia. Later, PME was identified in ticks collected from 10 U.S. states between 1998 and 2006 and is thought to have been present but not recognized in the U.S. rather than recently introduced. We propose here to characterize the PME agent in order to better define its relationship with E. ruminantium and to develop improved diagnostic methods to clearly differentiate these two pathogens.
Project Methods
The specific aims are: 1. Isolate and culture Florida strains of PME. Currently, PME has been detected in A. americanum ticks from Florida, but there is no culture method available or, indeed, a source to infect animals and determine pathogenicity. We propose to collect questing nymphal and adult ticks from areas where PME has been detected previously. Stabilates will be prepared from ticks and aliquots examined by PCR to determine the presence of PME infection. We will infect goats by live tick feeding or with known PME-infected tick stabilates and infected blood and tissues will be used to develop culture methods. 2. Compare the host cell, tissue distribution, and pathogenesis of the PME and E. ruminantium. Understanding the pathophysiology of the disease caused by PME is critical in being able to culture the organism as well as differentiate it from the disease caused by E. ruminantium. The tissues from infected goats will be examined via histopathology and PCR to better characterize PME infection and determine which cell types and tissues are infected with the organism as well as characterizing the pathology of the disease. 3. Determine cross-reactions in the goats between PME and Ehrlichia ruminantium. Cross-reactions between these two agents are important for two reasons. Firstly, prior persistent infection with PME may affect the course of disease caused by E. ruminantium. Secondly, we need to develop high-throughput DNA-based and serological tests such as real-time PCR and specific ELISAs to differentiate these two agents. We will conduct sequential infections with PME and E. ruminantium with our collaborators in Ross University. 4. Develop specific and convenient diagnostic tests to differentiate PME from E. ruminantium. Current diagnostic tests previously developed for Ehrlichia chaffeensis, Ehrlichia canis, E. ruminantium and PME will be modified for rapid and specific differentiation of the PME agent. DNA-based assays will be developed from genetic analysis based on comparing the Florida strain of PME with E. ruminantium. Using immune sera from experimentally infected animals and clinical cases, we will identify and characterize antigens that have the potential for species-specific identification of infected animals.