Animal Health (NP 103) Annual Report for 2006
The mission of the Animal Health Program is to conduct basic and applied research on selected diseases of economic importance to the United States livestock and poultry industries. The goals of the research mission are to produce knowledge and technology to reduce economic losses from infectious, genetic, and metabolic diseases of livestock and poultry. Cyril G. Gay, DVM, Ph.D, National Program Leader (NPL), Animal Health and Safety, is currently managing the program. ARS is actively recruiting for another NPL position to take the lead for bacterial and parasitic diseases of livestock and poultry. When the position is filled, Dr. Gay will take the lead on viral and prion diseases.
The Animal Health National Program will be starting a new five-year national program cycle starting Fiscal Year 2007. The Animal Health National Program currently includes 50 core research projects supported by 112 scientists located at 11 research sites throughout the country. The ARS research budget for the Animal Health Program Fiscal Year (FY) 2006 was $59 million (NTL), an increase of 5 percent over last year. Critical to the success of the research conducted at ARS is the ability to build and maintain the infrastructure of our laboratories to ensure the highest level of biosecurity and quality research. Accordingly, we are continuing to upgrade the animal research facilities at the National Animal Disease Center (NADC) in Ames Iowa. Construction of a high containment animal barn began in the fall of 2003 and is progressing. Design of a consolidated laboratory that will be used by NADC and the Animal and Plant Health Inspection Service (APHIS) is progressing.
Several of the scientists in the Animal Health National Program again received accolades this past year. Dr. Janice Miller received the first AVMA Lifetime Excellence in Research Award for achievement in veterinary medical research. Dr. Miller retired in 2003 from the ARS National Animal Disease Center (NADC). During her distinguished career, Dr. Miller discovered the bovine leukemia virus and developed some of the first tests to detect prion diseases such as Scrapie, CWD, and BSE.
Scientists within the National Animal Health Program were very active in their fields Fiscal Year (FY) 2006, with 83 articles published in peer-reviewed scientific journals. Many of the discoveries and findings were published in the popular press to reach our customers and stakeholder, including 7 articles in trade journals and book chapters. Technology transfer activities for the National Animal Health Program included 6 invention disclosures, 8 new Cooperative Research and Development Agreements (CRADA), 44 active Specific Cooperative Agreements (SCA), and 112 Material Transfer Agreements (MTA).
The following section of the report summarizes high impact research results addressing objectives in the current national program action plan.
Animal Health Research Highlights
Genetic Indicators of Leptospiral Evolution
Leptospirosis is one of the most common zoonotic diseases in the world, resulting in high morbidity and mortality in humans and affecting global livestock production. Most infections are caused by either Leptospira borgpetersenii or Leptospira interrogans,
bacteria that vary in their distribution in nature and rely on different modes of transmission. NADC scientists and colleagues in Australia reported this year the complete genomic sequences of two strains of L. borgpetersenii serovar Hardjo that have distinct phenotypes and virulence. These two strains have nearly identical genetic content, with subtle frameshift and point mutations being a common form of genetic variation. Limited regions of synteny (the preserved order of genes between related species and an indicator of divergent evolution) are shared between the large chromosomes of L. borgpetersenii and L. interrogans. Most interestingly, the L. borgpetersenii genome is ~700 kb smaller and has a lower coding density than L. interrogans, indicating it is decaying through a process of insertion sequence-mediated genome reduction. Loss of gene function is not random but is centered on
impairment of environmental sensing and metabolite transport and utilization. These features distinguish L. borgpetersenii from L.interrogans, a species with minimal genetic decay and that survives extended passage in aquatic environments before encountering a mammalian host. This landmark study indicates that L. borgpetersenii is evolving toward dependence on a strict host-to-host transmission cycle. (National Program 103 and Performance Measure 3.2.1)
Bulach, D.M, Zuerner, R.L, Wilson, P., Seemann, T., McGrath, A., Cullen, P.A, Davis, J., Johnson, M., Kuczek, E., Alt, D.P, Peterson-Burch, B., Coppel, R.L., Rood, J.I, Davies, J.K, Adler, B. 2006. Genome reduction in Leptospira borgpetersenii
reflects limited transmission potential. Proceedings of the National Academy of Science (PNAS). Vol. 103, no. 39, pp. 14560–14565.
Genetically Controlled Incubation Period of Chronic Wasting Disease (CWD) in Elk
CWD is a member of the Transmissible Spongiform Encephalopathy (TSE) family of disorders that includes Scrapie, Bovine Spongiform Encephalopathy (BSE), and Creutzfeldt-Jacob disease. CWD has a more limited host range and no evidence to date of a zoonotic potential. CWD is reported in free ranging and farm raised deer and elk in the U.S. and Canada. CWD is a relatively uncharacterized TSE with novel patterns of transmission and agent distribution, as well as providing the considerable challenge of controlling a persistent disease in free ranging wildlife. CWD in North America has resulted in the loss of domestic and foreign markets, restrictions on trade and movement of live animals, and the substantial costs associated with surveillance of hunter-killed animals. ARS scientists working at Washington State University in Pullman, WA, working in collaboration with National Animal Disease Center (NADC) Ames, IA, Colorado State University, and USDA APHIS Veterinary Services and Wildlife Services, documented this year the first association between Prnp codon 132 genotype and incubation time in elk with experimental CWD. This study included the characterization of the disease phenotype in elk homozygous and heterozygous for the highly susceptible Prnp allele, demonstrating that there were no differences in the eventual outcome of the disease, only in the incubation period. This information will be useful for producers and regulatory groups establishing minimum quarantine periods and elk movement requirements and providing guidance to investigators performing pathogenesis trials. (National Program 103 and Performance Measure 3.2.2)
Hamir, A.N., Gidlewski, T., Spraker, T.R., Miller, J.M., Creekmore, L., Crocheck, M., Cline, T., Orourke, K.I. 2006. Preliminary observations of genetic susceptibility of elk (Cervus elaphus nelsoni) to chronic wasting disease by experimental oral inoculation. Journal of Veterinary Diagnostic Investigation. 18(1):110-114.
Abnormal Prion Accumulation Associated with Retinal Pathology in Sheep with Scrapie
A study completed by scientists at the National Animal Disease Center (NADC) in collaboration with Iowa State University demonstrates that the retina responds to the accumulation to abnormal prion protein in a way that may affect visual system function. It could be shown by immunoreactivity of abnormal prions that specific cell populations of the retina were affected in scrapie-infected sheep. This study provides the first report that a prion disease in a natural host accumulates abnormal prions in the retina that is associated with pathology in the absence of overt morphologic changes indicative of retinal degeneration. This study provides additional information on abnormal prion tissue migration but may also provide new opportunities for early detection. (National Program 103 and Performance Measure 3.2.1)
Greenlee, J.J., Hamir, A.N., West Greenlee, M.H.. 2006. Abnormal Prion Accumulation Associated with Retinal Pathology in Experimentally Innoculated Scrapie-Affected Sheep. Vet Pathol. 43:733-739.
Comparative Genomic Analysis of Mycobacterium paratuberculosis (Johne’s) Isolates from Multiple Host Species
Scientists at the National Animal Disease Center (NADC) are capitalizing from the completion of their work sequencing the whole genome of M. paratuberculosis (bovine isolate K10) and are now conducting comparative microbial genomics studies. Unique sequences are being identified to generate diagnostics to study the epidemiology and ecology of M. paratuberculosis. The genomic DNA from a total of 35 M. paratuberculosis isolates was isolated and compared to the sequenced M. paratuberculosis of K10 isolate by competitive hybridization to DNA microarrays. Isolates were obtained from a variety of host species, including cattle, goats, sheep, bison, starlings, and humans. Analyses of the data generated from these studies is revealing that M. paratuberculosis isolates from sheep can be characterized by a series of inserted and deleted gene clusters, while the isolates obtained from other host species are highly similar to the sequenced isolate M. paratuberculosis K10. These findings will allow us to develop a more comprehensive understanding of the genetic diversity present among M. paratuberculosis isolates and may answer questions of transmission of M. paratuberculosis from one species to another, along with environmental and host pressures on the evolution of the microorganism. (National Program 103 and Performance Measure 3.2.1)
Marsh, I.B., Bannantine, J.P., Paustian, M., Tizard, M.L., Kapur, V., Whittington, R.J. 2006. Genomic Comparison of Mycobacterium avium subsp. paratuberculosis Sheep and Cattle Strains by Microarray Hybridization. Journal of Bacteriology. 188(6): 2290-2293.
Stabel, J.R., Bannantine, J.P. 2005. Development of a Nested PCR Method Targeting a Unique Multicopy Element, ISMap02, for Detection of Mycobacterium avium subsp. paratuberculosis in Fecal Samples. Journal of Clinical Microbiology. 43(9):4744-4750.
Inactivated Avian Influenza Vaccines Provide Protection Against Asian H5N1
Currently available killed adjuvanted H5 vaccines, including those in the U.S. National Veterinary Stockpile, were shown to provide protection to chickens after challenge from Asian H5N1 high pathogenicity (HP) avian influenza (AI) viruses. Killed AI vaccines have been used in Asia for the past 4 years to control H5N1 HPAI, but there are concerns that changes in the virus (caused by antigenic drift) may make these vaccines less protective. ARS scientists at the Southeast Poultry Research Laboratory in Athens, GA, determined that several H5 vaccines that have been used or are commercially available were still protective against a 2006 H5N1 HPAI virus isolated from a chicken in Hong Kong. The vaccine protected chickens from clinical signs and death when challenged with high dose of the 2006 H5N1 HPAI virus. In addition, the vaccine reduced the growth of the challenge virus in vaccinated chickens with no detectible shedding from the intestines and reduced shedding from the respiratory tract. These data indicate the H5 killed AI vaccines available for poultry provided excellent protection from the 2006 Hong Kong strains of H5N1 HPAI virus. (National Program 103 and Performance Measure 3.2.3)
Swayne, D.E., Lee, C.W., Spackman, E. 2006. Inactivated North American and European H5N2 avian influenza virus vaccines protect chickens from Asian H5N1 high pathogenicity avian influenza virus. Avian Pathology. 35(2):141-146.
Understanding the Role of Hypocalcemia in Dairy Cows and Disease Susceptibility
Hypocalcemia is common in periparturient dairy cows and is associated with decreased intracellular calcium stores in peripheral blood mononuclear cells (PBMC). ARS scientists at the National Animal Disease Center (NADC) completed studies that suggest this is the cause of a blunted intracellular calcium (Ca) release response to an immune cell activation signal. It is concluded that intracellular Ca stores decrease in PBMC before parturition and development of hypocalcemia. This suggests that systemic calcium stress precedes measurable hypocalcemia, particularly in cows that will develop milk fever. Therefore, PBMC intracellular Ca stores are a more sensitive measure of calcium stresses in transition cow. This decrease in PBMC intracellular Ca stores before parturition and the development of hypocalcemia contributes to periparturient immune suppression, supporting a link between decreased Ca and the immune system. The impact of this research is a more complete understanding of the role hypocalcemia plays in the complications of a hypocalcemic episode, such as increased disease susceptibility (National Program 103 and Performance Measure 3.2.2)
Kimura, K., Reinhardt, T.A., Goff, J.P. 2006. Parturition and hypocalcemia blunts calcium signals in immune cells of dairy cattle. Journal of Dairy Science. 89(7):2588-2595.
In vitro Model for Determining the Virulence of BVDV Strains
Different strains of Bovine Viral Diarrhea Virus (BVDV) cause different disease syndromes. Some cause very severe clinical disease and some cause very mild clinical disease. To date, the only way to determine if a virus caused severe disease (i.e. was a virulent virus) or caused mild disease (i.e. was an avirulent virus) was to infect animals with the virus and observe the results. This limited the research that could be done to determine why some viruses were virulent and others avirulent. Scientists at the National Animal Disease Center (NADC) developed a model that uses cultured cells rather that live animals to differentiate between virulent and avirulent viruses. The impact is that the use of this model may reduce the need to use live animals and will significantly cut the cost and difficulty of studying virulence in BVDV strains. Preliminary results generated with this model, indicate that BVDV virulence is associated with the death of cells associated with the immune system. (National Program 103 and Performance Measure 3.2.1)
Ridpath, J.F., Bendfeldt, S., Neill, J.D., Liebler-Tenorio, E. 2006. Lymphocytopathogenic activity in vitro correlates with high virulence in vivo for BVDV type 2 strains: criteria for a third biotype of BVDV. Virus Research. 118(1-2):62-69.