Research Programs and Projects at this Location : USDA ARS

ARS Home » Pacific West Area » Pullman, Washington » Animal Disease Research Unit » Research » Research Project #441168

Research Project: Control Strategies for Bovine Babesiosis

Location: Animal Disease Research Unit

2024 Annual Report

Objectives
This project aims to develop a risk mitigation plan to reduce threats associated with bovine babesiosis for the U.S. livestock industry. To develop bovine babesiosis control strategies, there are significant knowledge gaps regarding Babesia-mammalian-tick host interactions that need to be addressed. These gaps include a lack of understanding of Babesia stage-specific protein expression, limited knowledge regarding drug therapy efficacy and safety, and genetic conservation among geographically distinct Babesia isolates. Additionally, little progress has been made on characterizing the mechanisms regulating a protective immune response to bovine babesiosis, understanding the risk of introducing pathogens into disease-free regions by wildlife, and rapidly changing environmental factors. This plan will address these knowledge gaps by developing diagnostic assays for detecting cattle infected with Babesia spp., discovery and testing of potential Babesia antigen targets expressed by the parasite during its development within cattle or tick vectors, development of efficacious and safe treatment regimens to control babesiosis, characterizing the immune response to Babesia and identification of targets that can be used to develop a vaccine, and developing mathematical models to predict the spread of bovine babesiosis parasites into U.S. herds. This project will address the following objectives. Objective 1: Develop intervention strategies to minimize the impact of bovine babesiosis outbreaks, to include vaccine and therapeutic development to prevent clinical disease or block transmission of bovine babesiosis. Sub-objective 1A: Improve molecular and serologic diagnostic assays for bovine babesiosis. Sub-objective 1B: Evaluate the capacity of bovine antibodies against Babesia gamete and kinete surface antigens to minimize the impact of bovine babesiosis outbreaks. Sub-objective 1C: Assess the efficacy of chemotherapeutic approaches to eliminate Babesia pathogens and disrupt transmission. Objective 2: Characterize the immune response to infection with Babesia bovis, to include identifying targets that can be used as correlates of protection and examining age-specific differences. Sub-objective 2A: Investigate age-specific immune response differences to acute Babesia bovis infection between naïve young calves and adult cattle. Sub-objective 2B: Identify Babesia bovis proteins required to induce an immune response that mitigates disease severity. Objective 3: Develop predictive models of potential Babesia disease spread in the United States to assist in mitigating potential future outbreaks. Sub-objective 3A: Develop prediction models of potential Babesia parasite spread into the United States.

Approach
Objective 1: Develop intervention strategies to minimize the impact of bovine babesiosis outbreaks, to include vaccine and therapeutic development to prevent clinical disease or block transmission of bovine babesiosis. Goals: The research will focus on developing strategies for mitigating or preventing bovine babesiosis outbreaks. Specifically, 1) develop cost-effective diagnostic assays for detecting cattle infected with B. bovis and/or B. bigemina, which are major threats to the U.S. cattle industry, 2) evaluate bovine antibodies against Babesia tick stage-specific parasites for their capacity to prevent transmission and reduce acute disease, and 3) identify efficient drug(s) to clear infection to minimize the impact of bovine babesiosis outbreaks. Objective 2: Characterize the immune response to infection with Babesia bovis, to include identifying targets that can be used as correlates of protection and examining age-specific differences. Goals: The research will focus on a comprehensive characterization of the immune response of calves to infection with B. bovis and defining cytokines/chemokines associated with reduced disease severity. Also, Babesia surface proteins will be identified and utilized to understand immune mechanisms responsible for controlling Babesia infection within the mammalian host. The outcome will provide a strong foundation for future Babesia subunit vaccine development. Objective 3: Develop predictive models of potential Babesia disease spread in the United States to assist in mitigating potential future outbreaks. Goal: The research focus will be to develop and validate models that better predict areas at risk of Babesia parasite introduction into the United States.

Progress Report
This report documents FY 2024 progress for project 2020-22620-023-000D, “Control Strategies for Bovine Babesiosis”, which began in October 2021. In support of Objective 1, research has progressed on all sub-objectives. For Sub-objective 1A, molecular diagnostic assays, including conventional and quantitative polymerase chain reactions (PCRs), were developed to detect parasites in infected animals during chronic infection. These diagnostic methods were utilized to assess babesiosis in an endemic area. Additionally, proteins were expressed to determine if antibodies from infected animals react with the recombinant version of the proteins. Sera samples from long-term Babesia-infected animals were collected to demonstrate antibody reactivity to the candidate recombinant proteins. For Sub-objective 1B, cattle were immunized with proteins or a recombinant protein, and then infected with Babesia while ticks were applied to feed during the infection. The results showed that antibodies from immunized animals prevented tick infection and, consequently, the transmission of the parasite to susceptible animals. For Sub-objective 1C, novel babesicidal drugs were evaluated under in vitro conditions to determine their efficacy against Babesia parasite growth. The results showed no parasites were found after drug treatment, indicating that the drugs used in vitro conditions acted as effective babesiacidals. In support of Objective 2, progress has been made in all sub-objectives. For Sub-objective 2A, both adults and young animals were vaccinated and then exposed to virulent Babesia strains. The results indicated that vaccinated animals were protected against the disease, and all survived the challenge with virulent stain of the parasites. Blood samples were taken from vaccinated and challenged animals to identify the cytokines critical for controlling the manifestation of the disease. Regarding Sub-objective 2B, parasite proteins were identified and grouped as potential vaccine candidates. Recombinant proteins were produced, immunologically characterized, and tested in bovine vaccination trials to determine if immunization against Babesia recombinant proteins can protect against the disease. A conserved surface exposed B-cell epitope was recognized by antibodies in sera from protected bovines. In support of Objective 3, progress has been made on Sub-objective 3A by collecting additional data sets and initiating modeling to predict the potential spread of ticks and parasites. Data were collected regarding distribution of wildlife hosts, such as white-tailed deer and nilgai, known to harbor cattle fever ticks in Texas, to determine the potential exposure of cattle to ticks at the wildlife-livestock interface. Furthermore, data were collected to identify factors such as climate change and weather patterns that may affect wildlife distributions. Additionally, humidity and temperature data were collected to assess their impact on animal and tick distribution. Data on historical cattle fever tick infestations in Texas have also been collected.

Accomplishments
1. Identification of conserved babesia proteins that can serve as vaccine targets to block tick transmission. Ticks efficiently transmit Babesia parasites that cause significant economic loss for the cattle industry in much of the world. Babesia parasites pose a big risk for U.S. cattle and are transmitted by the tick vector, Rhipicephalus microplus. During tick infection, Babesia parasites transform into distinct life stages and undergo sexual reproduction, a process required for ongoing tick transmission. ARS researchers in Pullman, Washington, discovered species conserved proteins that may be essential for the parasite lifecycle and subsequent transmission and can be the targets of protective immune responses. These conserved proteins will serve as robust candidates for vaccine development that can disrupt the parasite lifecycle in the tick and thus prevent transmission of Babesia parasites in endemic areas of the world.

2. Nilgai antelope are not susceptible to Babesia parasites. Determining the susceptibility of nilgai to Babesia parasites is crucial for assessing the risk of bovine babesiosis entering the United States. These parasites can cause mortality rates of up to 90% in cattle that have not been previously exposed to them. ARS researchers in Pullman, Washington, conducted tests to see if Babesia parasites were present in cattle or in nilgai after challenging with live parasites. The results showed that nilgai did not exhibit signs of infection by molecular tests when exposed to Babesia parasites. Given their potential to spread ticks over long distances in the United States, controlling ticks on nilgai is a top priority. These findings will assist the Texas Animal Health Commission in developing a more effective strategy to prevent babesiosis from entering the United States.

3. Development and application of an in vitro tick feeding system to study tick borne diseases. Ticks are known for transmitting most arthropod-borne diseases to livestock globally. Due to climate change, ticks have expanded into regions that were once considered tick-free, interacting with wildlife, livestock, and humans, leading to the spread of tick-borne pathogens. Traditionally, researchers have relied on animal models to understand tick biology and pathogen transmission, which has limitations including reproducibility of experiments, individual animal variation, and the requirement for large numbers of animals. To address these challenges, ARS researchers in Pullman, Washington, have developed a novel in vitro tick-feeding system, which will contribute to the replacement, reduction, and refinement of animals used in research, allowing for the development of more effective strategies for controlling ticks and the pathogens they transmit. This advancement is of great significance in medical and veterinary research.

U.S. DEPARTMENT OF AGRICULTURE

Animal Disease Research Unit: Pullman, WA