A young man who works on a ranch and lives in the log bunkhouse experiences sudden fever with muscle aches. A few days later he begins to cough and have difficulty breathing, and goes to an urgent care clinic. His blood pressure is low. A blood sample reveals a low platelet count. A Gram stain of a sputum sample shows only a few small bacteria present. Which of the following is the most likely infecting agent? A) Bacillus anthracis
B) Hantavirus
C) Histoplasma capsulatum
D) influenza
E) Mycoplasma pneumonia

The correct answer is: B) Hantavirus.

Explanation:

Hantavirus is an infectious disease caused by a family of viruses that exist in rodents such as rats. These viruses can either cause Hantavirus Pulmonary Syndrome (HPS), especially in the Americas; or Hemorrhagic Fever with Renal Syndrome (HFRS), which is most common in Europe and Asia.

The young man described has symptoms that match the common symptoms of Hantavirus Pulmonary Syndrome, such as fever and muscle aches (known as the 'early symptoms'), as also coughing and having difficulty breathing (known as the 'late symptoms'). Some of these symptoms can easily be confused with Influenza, but the shortness of breath and the fact that the patient has a history of working and living in a rural environment suggest Hantavirus.

HPS also produces a low platelet count and high white cell count.

Infection by Bacillus anthracis is uncommon, plus the lack of symptoms that match the disease (such as a sore throat) and the existence of muscle aches in the patient (which does not match Anthrax) can help discard this option.

Histoplasma capsulatum is a fungus that can cause lung infection when its spores are inhaled. Its symptoms are similar to HPS but with the addition of red bumps in the legs and joint pain, not muscle aches.

Mycoplasma pneumonia is a bacteria that produces pneumonia. Most of its symptoms match the patient except for the lack of a sore throat.