Review Question - QID 108810

The most likely diagnosis in this patient is rabies. Rabies is a (-) single-strand RNA virus.

In this patient with malaise, agitation, photophobia, fever, and a history spelunking, rabies should be high on the differential diagnosis. Rabies is a virus that is transmitted via bat, raccoon, and dog bites. After the initial bite, the virus binds to post-synaptic acetylcholine receptors before traveling via retrograde transport from the peripheral nervous system to the central nervous system. It has a long incubation period (weeks to months) before symptom onset. Rabies is an enveloped (-) single-stranded sense RNA bullet-shaped virus of the rhabdovirus family. Due to their complex structure, (-) single-stranded RNA viruses are able to evade the host innate immune response. That partly explains why single-stranded RNA viruses such as rabies, Ebola virus, Marburg virus, hantavirus, influenza, measles, and mumps often cause severe, life-threatening infections.

Illustration A demonstrates the characteristic appearance of Negri bodies, which are pathognomonic of rabies. Negri bodies are collections of virions within the cytoplasm of a neuron and can be identified on examination of tissue from a brain biopsy. On histology, they resemble eosinophilic inclusion bodies. Negri bodies are most commonly found in the hippocampus and cerebellum.

Incorrect Answers:
Answer 2: (+) single-stranded RNA viruses include members of the picornavirus, calicivirus, togavirus, flavivirus, coronavirus, retrovirus, and hepevirus families. These viruses cause a wide array of diseases ranging from the common cold to meningitis, encephalitis, poliomyelitis, hepatitis, and human immunodeficiency virus (HIV).

Answer 3: Double-stranded RNA viruses include rotavirus, a member of the reovirus family. Rotavirus is the most common cause of diarrheal disease among infants and young children. It typically presents with fever, watery diarrhea, nausea, and vomiting.

Answer 4: Non-enveloped DNA viruses include members of the adenovirus, papillomavirus, polyomavirus, and parvovirus families. These viruses cause a variety of diseases. For example, adenovirus is known to cause conjunctivitis, tonsillitis, bronchitis, gastroenteritis, meningitis, and encephalitis.

Answer 5: Enveloped DNA viruses include members of the herpesvirus, hepadnavirus, and poxvirus families. These virus families are very diverse and cause a wide-ranging array of diseases including orolabial and genital herpes, shingles, mononucleosis, hepatitis, smallpox, and molluscum contagiosum.

Bullet Summary:
Rabies presents with fever, hydrophobia, seizures, and other CNS symptoms following a bite from an infected dog, raccoon, or bat. The rabies virus is a (-) single-stranded RNA virus.