IMMUNITY FACTORS IN PNEUMOCOCCUS INFECTION IN THE DOG

Area of Science:

• Microbiology
• Immunology
• Pathology

Background:

• Intravenous inoculation of virulent pneumococci causes septicemia and meningitis in dogs.
• Pneumococci initially disappear from circulation but reappear 24-48 hours later.

Purpose of the Study:

• To investigate the mechanism of pneumococcal reinvasion of the bloodstream.
• To understand the role of host antibodies in pneumococcal infections.
• To explore the factors influencing the course and outcome of pneumococcal septicemia and meningitis.

Main Methods:

• Intravenous inoculation of dogs with virulent pneumococci.
• Monitoring pneumococcal levels in circulation over time.
• Reinoculation experiments during different stages of infection.
• In vitro testing of pneumococcal resistance to immune sera (agglutinins and opsonins).
• Observation of phagocytosis in relation to disease severity.

Main Results:

• Pneumococci initially cleared via agglutination and sequestration in organs.
• Reinvading pneumococci exhibit resistance to existing antibodies, suggesting adaptation rather than antibody exhaustion.
• Reinoculation during septicemic crisis leads to more rapid antibody-mediated clearance.
• Antibodies are active in vivo during crisis, preceding in vitro detectable changes.
• Pneumococci isolated during convalescence are more susceptible to immune sera.
• Phagocytosis is inversely correlated with meningitis severity.

Conclusions:

• Pneumococcal reinvasion is attributed to acquired resistance to host antibodies.
• In vivo antibody activity can precede in vitro detection.
• The adaptation of pathogens to host conditions may explain incubation periods.
• Transmission during the ascending stage of infection can lead to epidemics due to pathogen adaptation.
• Weakening of the infectious agent by acquired antibodies during convalescence contributes to epidemic subsidence.