Pneumonia occurs if the organisms are inhaled into the lungs and not cleared (again, viral infection, or smoking-induced ciliary paralysis might be contributing factors). The organisms polysaccharide capsule makes it resistant to phagocytosis and if there is no pre-existing anticapsular antibody alveolar macrophages cannot adequately kill the pneumococci. The organism spreads to the blood stream (where it can cause bacteremia) and is carried to the meninges, joint spaces, bones, and peritoneal cavity, and may result in meningitis, brain abscess, septic arthritis, or osteomyelitis.S. pneumoniae has several virulence factors, including the polysaccharide capsule mentioned earlier, that help it evade a hosts immune system. It has pneumococcal surface proteins that inhibit complement-mediated opsonization, and it secretes IgA1 protease that will destroy secretory IgA produced by the body and mediates its attachment to respiratory mucosa.The risk of pneumococcal infection is much increased in persons with impaired IgG synthesis, impaired phagocytosis, or defective clearance of pneumococci. In particular, the absence of a functional spleen, through congenital asplenia, surgical removal of the spleen, or sickle-cell disease predisposes one to a more severe course of infection (overwhelming post-splenectomy infection) and prevention measures are indicatedPeople with a compromised immune system, such as those living with HIV, are also at higher risk of pneumococcal disease. In HIV patients with access to treatment, the risk of invasive pneumoccal disease is 0.2–1% per year and has a fatality rate of 8%.There is an association between pneumococcal pneumonia and influenza.
Diagnosis
Diagnosis of Angiostrongyliasis is complicated due to the difficulty of presenting the angiostrongylus larvae themselves, and will usually be made based on the presence of eosinophilic meningitis and history of exposure to snail hosts. Eosinophilic meningitis is generally characterized as a meningitis with >10 eosinophils/μL in the CSF or at least 10% eosinophils in the total CSF leukocyte count. Occasionally worms found in the cerebrospinal fluid or surgically removed from the eye can be identified in order to diagnose Angiostrongyliasis. Lumbar puncture
Lumbar puncture should always be done in cases of suspected meningitis. In cases of eosinophilc meningitis it will rarely produce worms even when they are present in the CSF, because they tend to cling to the end of nerves. Larvae are present in the CSF in only 1.9-10% of cases. However, as a case of eosinophilic meningitis progresses, intracranial pressure and eosinophil counts should rise. Increased levels of eosinophils in the CSF is a hallmark of the eosinophilic meningitis. Brain imaging
Brain lesions, with invasion of both gray and white matter, can be seen on a CT or MRI. However MRI findings tend to be inconclusive, and usually include nonspecific lesions and ventricular enlargement. Sometimes a hemorrhage, probably produced by migrating worms, is present and of diagnostic value. Serology
In patients with elevated eosinophils, serology can be used to confirm a diagnosis of angiostrongyliasis rather than infection with another parasite.