= Solution
\b[<Typhus> and <typhoid fever> are distinct infections, despite their overlapping fever, prostration and delirium.] In the British historical comparison, typhus chiefly means epidemic louse-borne <typhus>, not every disease now called a typhus fever.
Classical <typhus> often begins relatively abruptly with severe headache, fever, prostration and a conspicuously ill mental state. Its eruption is commonly a more extensive dusky maculopapular rash on the <anatomical trunk> and limbs and may become petechial. Crowded conditions and infestation with body lice support the epidemiological distinction. Modern knowledge identifies <Rickettsia prowazekii> and transmission involving infected louse material. Injury to small-vessel <endothelium> helps explain the widespread illness; it is not chiefly a local ulcerating disease of the ileal lymphoid tissue.<Clinical Overview of Epidemic Typhus by CDC>[Transmission; clinical characteristics; rash and small-vessel injury]{ref}
<Typhoid fever> more often develops insidiously, with persistent fever, headache and progressive weakness, together with abdominal discomfort, distension and either constipation or <diarrhoea>. Sparse, transient rose spots may occur on the <anatomical trunk>. Splenic enlargement and intestinal complications are important. The characteristic pathological process involves intestinal lymphoid tissue, especially <Peyer's patches> in the terminal <ileum>, with enlargement, <necrosis> and ulceration. Severe ulcers can bleed or perforate.<Typhoid Fever in StatPearls>[Pathophysiology and histopathology: intestinal lymphoid lesions and complications]{ref}
Modern causation separates <typhoid fever>, due to <Salmonella Typhi>, from louse-borne <typhus>. <Typhoid fever> spreads through food or water contaminated by human excreta, including material from carriers; it is not acquired merely because an air space is crowded. A prolonged course, abdominal findings and intestinal haemorrhage favour it, whereas abrupt severe illness with a widespread dusky rash and louse exposure favour <typhus>.<Typhoid and Paratyphoid Fever in the CDC Yellow Book>[Infectious agent; transmission; clinical presentation and complications]{ref}
Neither the rash nor the bowel habit is invariable, and the old contrast between an approximately two-week typhus and a longer enteric illness is a tendency, not a diagnostic clock. An absent rose spot does not exclude <typhoid fever>, and an absent rash does not exclude <typhus>. Modern confirmation uses organism-appropriate investigations, including <blood culture> for enteric fever and appropriate serological or molecular testing for <typhus>. The important historical achievement is the separation of the syndromes; the later microbiological explanation should not be projected into every 1864 diagnostic account.
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