Dermatophyte infections are named for the site they affect, and capitis specifically designates the scalp. Tinea capitis is therefore an infection of the scalp by dermatophytes that invade hair follicles, causing scaling and sometimes hair loss. The other sites—hands, feet, and nails—have their own name variants (manuum, pedis, unguium), so they describe infections at those locations rather than the scalp. In short, the scalp is the correct site because capitis means scalp involvement.

In virus taxonomy, groups are arranged from broad to specific to reflect relatedness and shared traits. The order is the broadest level among these ranks, followed by family, then subfamily, then genus, and finally species, which is the most specific unit. This structure makes sense because a single order contains several families that share major characteristics; within a family, subfamilies can group more closely related genera; genera encompass species that are very similar in important ways; and species define a distinct lineage with its own properties. Naming conventions reinforce this hierarchy, with family names ending in -viridae, subfamily in -virinae, genus in -virus, and species typically named as a specific virus.

SARS is caused by a coronavirus. Coronaviruses are enveloped, positive-sense RNA viruses with spike proteins on their surface that give a crown-like appearance. They primarily affect the respiratory tract and can cause a range of illnesses from mild colds to severe pneumonia. The other listed viruses do cause respiratory illness but are not responsible for SARS: rhinovirus is a picornavirus that typically causes common colds; adenovirus is a non-enveloped dsDNA virus with different disease patterns; influenza virus is an orthomyxovirus with segmented negative-sense RNA that causes flu. So the coronavirus is the culprit behind SARS.

Cryptosporidium is the parasite that causes cryptosporidiosis. It’s a tiny protozoan whose life cycle includes hardy oocysts that can survive in water and food, making waterborne and foodborne transmission common. In healthy individuals, infection often leads to watery diarrhea, abdominal cramps, and nausea that usually resolves, but it can be more severe and prolonged in immunocompromised people. Understanding what each organism typically causes helps connect the name to the disease: Giardia intestinalis leads to giardiasis with greasy, malabsorptive stools; Entamoeba histolytica causes amoebic dysentery and can form liver abscesses; Plasmodium falciparum is the agent of malaria with fever cycles and red blood cell invasion. Cryptosporidium specifically points to cryptosporidiosis, matching the clinical picture of watery diarrhea and the parasite’s distinctive oocyst form.