The pathogenesis of Rhodococcus equi pneumonia in foals.
Abstract: The pathogenesis of Rhodococcus equi pneumonia in foals is reviewed. The main routes of infection are respiratory and alimentary. The latter is probably the chief route of exposure in all foals and probably leads to development of specific immunity. Susceptible foals, those whose maternal immunity wanes before generation of their own immune response, readily develop disease if exposed aerogenously to sufficient numbers of R. equi. Management and environmental circumstances have a major role to play in determining the magnitude of this challenge and, therefore, in the prevalence of the disease. Infection of a naive foal leads to severe, suppurative bronchopneumonia with suppurative lymphadenitis of regional nodes and, in approximately 50% of animals, to necrotizing enterocolitis. The foal is uniquely susceptible to R. equi pneumonia; comparable experimental infections do not produce progressive destructive pulmonary lesions in other animal species. In the naive foal lung, R. equi behaves as a facultative intracellular pathogen, avoiding destruction within the alveolar macrophage by inhibiting phagolysosome fusion and possibly by causing lysosomal degranulation. The role of putative virulence factors, such as equi factor, remains to be elucidated.
Publication Date: 1987-08-01 PubMed ID: 3314108DOI: 10.1016/0378-1135(87)90109-xGoogle Scholar: Lookup
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Summary
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This research article explores the process and causes of pneumonia caused by the bacterium Rhodococcus equi in young horses, or foals. Both respiratory and alimentary infection routes are discussed, with alimentary exposure identified as likely leading to disease resistance. The study also reveals the significant impact of environmental conditions and the roles of immunity, as well as specific disease characteristics and the unique susceptibility of foals to this type of pneumonia.
Routes of Infection
- The article identifies two primary pathways by which the bacterium Rhodococcus equi can infect foals: respiratory and alimentary (relating to the function of nutrition).
- Though both infection routes contribute to the overall problem, the alimentary route is deemed to be the main exposure pathway. This route, as the article suggests, appears to lead also to the development of specific immunity in affected foals.
Role of Immunity and Infectious Exposure
- Foals whose maternal immunity lessens before they have developed their own immune response are more likely to develop disease, especially if they are exposed to enough R. equi bacteria through the air (aerogenously).
- The paper stresses the substantial role that management, environment and exposure to the bacteria play, highlighting these factors as significant determiners of the disease’s prevalence.
Presentation and Impact of the Disease
- R. equi pneumonia is of particular concern in foals, who are uniquely susceptible. In contrast, similar experimental infections do not cause the same level of progressive lung damage in other animal species.
- When a foal with no prior exposure (a naive foal) is infected, severe bronchopneumonia develops, along with lymph node inflammation. In half of the cases, this leads to necrotizing enterocolitis, which is a devastating intestinal disease that often leads to death.
The Behaviour of R. equi Bacteria in Foals
- Within a naive foal lung, the R. equi bacteria acts as a facultative intracellular pathogen, meaning it has the ability to live both inside and outside of host cells. In this capacity, it avoids destruction within the lungs’ immune cells by blocking the fusion of phagosomes and lysosomes, crucial compartments within a cell that degrade pathogens.
- Further research is yet to determine the roles of putative virulence factors (molecules which increase the bacteria’s capacity to cause a disease), such as the equi factor.
Cite This Article
APA
Yager JA.
(1987).
The pathogenesis of Rhodococcus equi pneumonia in foals.
Vet Microbiol, 14(3), 225-232.
https://doi.org/10.1016/0378-1135(87)90109-x Publication
Researcher Affiliations
- Department of Pathology, Ontario Veterinary College, University of Guelph, Ontario, Canada.
MeSH Terms
- Actinomycetales Infections / etiology
- Actinomycetales Infections / veterinary
- Animals
- Animals, Newborn
- Horse Diseases / etiology
- Horse Diseases / microbiology
- Horses
- Pneumonia / etiology
- Pneumonia / microbiology
- Pneumonia / veterinary
- Rhodococcus
Citations
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