Asplenia increases susceptibility to infection with which group of pathogens?

• A. Encapsulated bacteria (e.g., Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis)
• B. Fungal pathogens
• C. Nonenveloped viruses
• D. Obligate intracellular bacteria

Answer: (A)

The spleen plays a key role in clearing bloodstream infections caused by bacteria with polysaccharide capsules. It contains marginal zone B cells that produce IgM against these polysaccharide capsules and splenic macrophages that efficiently opsonize and remove encapsulated organisms from the blood. When the spleen is absent or not functioning, this opsonization-driven clearance is impaired, so encapsulated bacteria are able to cause invasive infections more readily. Examples like Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis reflect this vulnerability. Other pathogen types, such as fungi or nonenveloped viruses, aren’t as dependent on splenic opsonization, and obligate intracellular bacteria are controlled mainly by cell-mediated immunity, not by splenic clearance. So asplenia most strongly increases susceptibility to encapsulated bacteria.