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Protecting Animal Health through Disease Detection, Prevention, and Control

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The ARS animal health research program protects and ensures the safety of the nation’s agriculture and food supply through improved disease detection, prevention, and control. With support from the ARS Office of International Research Engagement and Cooperation, ARS leads and coordinates global alliances to prevent, control, and—when possible—eradicate diseases such as foot-and-mouth disease and African swine fever. The following accomplishments highlight ARS advances in animal health research in FY 2020.

Development of a safe and effective African swine fever virus vaccine. African swine fever (ASF) is a devastating and highly lethal disease of pigs for which there are no commercial vaccines. One of the most significant knowledge gaps that has hindered scientists from developing a safe and effective ASF vaccine is the lack of genomics information on the function of the virus’s 150 genes. ARS scientists at Orient Point, NY, successfully developed genetic engineering techniques that systematically delete genes from the ASF viral genome to determine their function. Pathogenicity studies in pigs with these altered viruses led to the discovery of essential genes for ASF viral replication, host immune evasion, and determinants of virulence. Gene identification provides potential targets for a rational design of safe and efficacious gene-deleted vaccines. The most recent vaccine candidate is the discovery of a genetically engineered gene-deleted live attenuated vaccine strain called ASFV-G-delta I177L. This vaccine strain was shown to be safe and effective and exceeded the performance of other ASF vaccine candidates. For the first time, the ASFV-G-delta I177L vaccine was shown to fully protect pigs against ASF with a low dose of vaccine virus. The safety characteristics of the vaccine include no adverse events even when high doses of the vaccine were administered to pigs. A patent covering the development ASFV-G-delta I177L was filed and several commercial partners initiated the process of licensing ASFV-G-delta I177L. ARS scientists have established an agreement with one of these companies to initiate the commercial development of the vaccine.

Predicting susceptibility of different species to infection with SARS-CoV-2. Viruses need to enter a cell to replicate and cause infection. Viral entry begins with attachment between a virus protein and a cell receptor(s), which allows the virus to enter the cell. Once inside the cell, the virus initiates replication and starts the race between host immunity and infection. For coronaviruses, the spike protein on the viral surface is responsible for cell receptor binding and cell entry. Several groups report that SARS-CoV-2 uses the angiotensin-converting enzyme 2 (ACE2) as the primary receptor for cell attachment. The susceptibility of both wild and domestic animals to SARS-CoV-2 and the potential for its zoonotic transmission is a public health concern. Assessing the potential for zoonotic transmission includes: (1) screening to identify the animal species that was infected originally and passed SARS-CoV-2 to humans; (2) determining if animal hosts can amplify SARS-CoV-2, which could increase its infectious potential; and (3) determining the current risk of infected people passing the virus to animals, particularly domestic species. The latter could result in an amplifying zoonotic cycle of human to animal to human transmission that could worsen SARS-CoV-2 evolution and prevalence. ARS researchers in Ames, IA, evaluated cross-species ACE2 genetic diversity in expression and functionality to determine susceptible tissue types and susceptibility of different animal species to SARS-CoV-2. The analysis predicted the limited potential of livestock transmission of SARS-CoV-2. Results also revealed that evolutionary changes in the genetic sequence of ACE2 receptors in domestic animals, including dogs, pigs, cattle, and goats, may have resulted in restricting SARS-CoV-2 infections.

Duration of foot-and-mouth disease contagion in infected live pigs and carcasses. Data-driven modeling of high-consequence foreign animal disease outbreaks is a critical component of veterinary preparedness. However, research and data are needed to address knowledge gaps in disease dynamics and modeling. ARS scientists in Orient Point, NY, conducted a study to address two major gaps in knowledge of foot-and-mouth disease virus (FMDV) pathogenesis in pigs: 1) the duration of the infectious period; and 2) the viability of FMDV in decaying carcasses. ARS scientists demonstrated that infected pigs transmitted disease at 10 days post infection (dpi), but not at 15 dpi. Assuming a latent period of 1 day, this results in a conservative estimate of 9 days infectious duration, which is considerably longer than suggested by previous research conducted with cattle. The residual airborne contagion diminished within 2 days of removal of infected pigs from isolation rooms. Furthermore, FMDV in muscle was inactivated within 7 days in carcasses stored at 4oC. By contrast, FMDV infectivity in vesicles harvested from intact carcasses stored under similar conditions remained remarkably high until the study termination at 11 weeks post-mortem. This information may be used to update models used for foot-and-mouth disease outbreak simulations involving areas of substantial pig production and emphasizes that infected carcasses can be a potential source of virus contamination and must be handled properly to prevent FMDV transmission.

Validation of an international standard for testing bovine tuberculosis. Bovine tuberculosis, caused by the bacterium Mycobacterium bovis, is a global problem impacting international and domestic trade. Harmonization and acceptance of diagnostic tests for bovine tuberculosis are important production and trade issues. ARS scientists in Ames, IA, worked internationally with other bovine tuberculosis research labs and the World Organization for Animal Health to evaluate and validate a new international standard tuberculin, a sterile protein extract of M. bovis that is used for skin testing cattle for bovine tuberculosis. This new standard creates a global organized system to ensure uniform testing worldwide. These findings will benefit regulatory agencies, veterinarians, and livestock producers involved with maintaining the tuberculosis-free status for the United States.