A research laboratory is studying the pathogenesis of respiratory syncytial virus (RSV) infection in infants.
They find that a specific viral surface glycoprotein is primarily responsible for attachment to host cells. This glycoprotein is:

A patient who received a solid organ transplant develops a pneumonia. Bronchoalveolar lavage fluid is positive for a single-stranded RNA virus that can cause giant cell formation with intranuclear and intracytoplasmic inclusions. The MOST likely causative agent is:

A patient returning from a mission trip to Africa presents with fever, headache, and a characteristic relapsing pattern of symptoms. Peripheral blood smear reveals the presence of extracellular flagellated protozoa. The MOST likely diagnosis is African trypanosomiasis caused by:

A patient with severe combined immunodeficiency (SCID) develops a progressive respiratory illness.
Bronchoalveolar lavage fluid is examined using direct fluorescent antibody (DFA) staining, which reveals numerous cysts of Pneumocystis jirovecii. The cysts appear:

A clinical laboratory receives a cerebrospinal fluid (CSF) sample from a 65-year-old patient presenting with fever, headache, and nuchal rigidity. Gram stain reveals Gram-positive cocci in pairs and short chains. Culture on blood agar grows alpha-hemolytic colonies that are optochin-susceptible and bile soluble. Which organism is most likely identified?