The oldest known vector-borne disease turned up in Chile

Scrub typhus is the oldest known vector-borne infection. Until recently it
was almost exclusively reported from the "tsutsugamushi triangle" within
the Asia-Pacific region, where Orientia tsutsugamushi causes roughly **1
million cases a year** with a **case fatality rate of about 7% if not
adequately treated.**

Then it was found in southern Chile — across almost 1,240 miles (2,000 km)
from the Biobío Region down to Tierra del Fuego — caused by **a novel species,
Candidatus Orientia chiloensis**, and carried by **larval trombiculid mites
of the genus Herpetacarus** (chiggers).

The outbreak

14 January – 14 February 2023: 36 suspected cases in the **Los Lagos
Region**. A suspected case met at least two of three criteria: **acute febrile
illness**, a generalised maculopapular rash, and the presence of a
necrotic lesion (eschar).

22 (79%) were acquired at the patient's own home; six (21%) while
travelling within the region.

The diagnostic breakdown is the practical lesson: **more than half the
confirmations came from the eschar and nothing else.** A clinician who takes
blood and does not sample the necrotic lesion would have missed 16 of 28.

Why it rose, honestly

Understanding the increase requires further eco-epidemiological studies.
The report offers three candidates and does not choose between them:

• Seasonality — **97% of Chilean cases to date have occurred during the
  austral summer, December–March**, and this was January–February
• More outdoor activity after two years of pandemic restrictions
• Growing awareness, producing more testing and reporting

The third would make part of the 450% an artefact of looking. That is worth
saying plainly rather than leaving as an implication.

Why it gets missed

**Because of its nonspecific clinical characteristics, scrub typhus might be
easily overlooked, and diagnosis requires a high index of suspicion.** Fever
and a rash are the beginning of a very long list.

Rapid diagnosis and treatment are crucial to avoid severe disease and
complications: pneumonia, renal failure, meningoencephalitis. **If
infection is suspected, treatment with doxycycline should be started without
delay** — before confirmation, because the confirmation takes longer than the
disease allows.

The part aimed at doctors nowhere near Chile

**Exposure to trombiculid mites is associated with outdoor activities and
affects not only rural residents but travellers on camping and trekking
trips.** With ecotourism growing in southern Chile, the report's audience
is explicitly **physicians worldwide who see ill travellers returning from the
region** — people who will present in a clinic that has never seen a case.

There is no vaccine. Prevention is exposure avoidance: **avoid contact
with low vegetation and soil**, wear long sleeves and trousers, **treat
boots and clothing with 0.5% permethrin**, and use **repellents containing
DEET or another EPA-registered active ingredient effective against chiggers**
on exposed skin and clothing.

Source: Centers for Disease Control and Prevention, MMWR.