Location: Virus and Prion Research
2023 Annual Report
Accomplishments
1. Streptococcus suis isolates obtained from within the U.S. did not harbor genes encoding the capacity to cause disease in humans. Most genomic sequence data needed to evaluate any potential risks attributed to S. suis is derived from isolates obtained outside the U.S. To help fill this gap, ARS researchers in Ames, Iowa, applied genome sequencing methods to examine the genetic makeup of S. suis isolates obtained within the U.S. These isolates were found to be genetically different from each other, indicating that they can give and receive genetic material from other bacteria. These isolates were also found to contain a high number of antimicrobial resistance genes, however, no genes encoding the capacity to cause disease in humans were found in these isolates. Collectively, this data provides a blueprint for addressing public and animal health concerns relating to the severity of disease caused by S. suis for producers, veterinarians, and public health officials.
2. Immunity to the key component of the outermost part of bacterial cell wall is not essential for protection against all Glaesserella parasuis strains. Glaesserella parasuis causes severe disease and death in pigs. It is a significant economic burden for pork producers. Producers control G. parasuis with vaccines, but research indicates vaccines may provide protection against only a single strain or capsule type (serotype). Capsule is a polysaccharide coating that surrounds bacteria and provides protection from the host immune system. To understand the role of capsule directed immunity in preventing G. parasuis disease, ARS researchers in Ames, Iowa, investigated the use of a G. parasuis mutant strain that does not produce a capsule as an inactivated vaccine. The capsule mutant vaccine was compared with a vaccine made from the wildtype strain (serotype 5). The capsule mutant protected pigs against the wildtype strain and multiple heterologous serotypes of G. parasuis including type 1, 4 and 13. However, when animals were challenged with a highly pathogenic serotype 5 strain, capsule specific protection was required for protection. These results are important to inform producers and veterinarians on the importance of strain selection for G. parasuis vaccines, especially for highly pathogenic isolates. This understanding will improve vaccine selection and reduce losses due to G. parasuis.
3. Bordetella bronchiseptica infection causes increases in the prevalence of other respiratory pathogens in swine. B. bronchiseptica causes respiratory infections in pigs, including pneumonia and atrophic rhinitis. It colonizes the nasal cavity and can alter the bacteria present (microbiota). To better understand the interactions between B. bronchiseptica and the normal microbiota of the nasal cavity, ARS researchers in Ames, Iowa, exposed pigs to B. bronchiseptica and compared the nasal microbiota between exposed and non-exposed pigs. This data shows the impact of B. bronchiseptica infection on the normal microbiota of the nasal cavity. Increases in respiratory pathogens following B. bronchiseptica exposure may contribute to the development of more complicated respiratory disease. This work contributes to the general understanding of the complex nature of respiratory infections in pigs and provides important information about interactions between B. bronchiseptica and other respiratory pathogens. This understanding will improve vaccine development and mitigation strategies for reducing economic losses due to B. bronchiseptica infection.
4. Bordetella bronchiseptica infection causes increased colonization but not disease with Streptococcus suis. B. bronchiseptica causes pneumonia in pigs and contributes to complex respiratory infections called porcine respiratory disease complex (PRDC). Coinfection with B. bronchiseptica increases the severity of disease with other respiratory pathogens. B. bronchiseptica infection can also increase nasal colonization with other pathogenic bacteria. S. suis is a systemic pathogen of pigs but also contributes to PRDC. To evaluate the interactions between B. bronchiseptica and S. suis, ARS researchers in Ames, Iowa, assessed colonization and disease in pigs exposed to B. bronchiseptica, S. suis, or both. Nasal colonization with S. suis was increased by coinfection with B. bronchiseptica; however, there was no increase in S. suis associated disease. Though no increase in disease was observed, increased colonization could have important implications when animals are stressed or immunocompromised, such as at weaning or during transport. This work provides important information on bacterial-bacterial interactions in the swine upper respiratory tract and contributes to the understanding of the role of B. bronchiseptica in PRDC as both a primary agent and contributor to more complicated infections is key information needed to develop vaccines needed to reduce losses due to B. bronchiseptica infection.
Review Publications
Hau, S.J., Buckley, A.C., Brockmeier, S. 2022. Rapid application of long-acting ceftiofur can prevent death losses associated with Streptococcus equi subspecies zooepidemicus in pigs. Swine Health and Production. 30(5):292-297. https://doi.org/10.54846/jshap/1298.
Nicholson, T.L., Bayles, D.O. 2022. Comparative virulence and antimicrobial resistance distribution of streptococcus suis isolates obtained from the United States. Frontiers in Microbiology. 13. https://doi.org/10.3389/fmicb.2022.1043529.
Hau, S.J., Nielsen, D.W., Mou, K.T., Alt, D.P., Kellner, S., Brockmeier, S. 2023. Resilience of swine nasal microbiota to influenza A virus challenge in a longitudinal study. BMC Veterinary Research. 54:Article 38. https://doi.org/10.1186/s13567-023-01167-9.
Nicholson, T.L., Shore, S. 2022. Genome sequences of Streptococcus suis isolates obtained from pigs in the United States between 2015 and 2017. Microbiology Resource Announcements. 11(8):e01067-21. https://doi.org/10.1128/mra.01067-21.
