Scrub typhus is an acute, infectious illness. Globally, more than a billion people are at risk for scrub typhus and an estimated one million cases occur annually. In this part of our COVID coinfection series, we present to you the diagnosis and line of treatment for scrub typhus alongside COVID-19.

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Pathogenesis

The mite Leptotrombidium deliense transmits scrub typhus. Vector mites like to live in well-defined patches of soil with a favourable micro ecosystem (mite islands). Humans become sick when they enter these mite islands and are bitten by the larvae of the mites (chiggers). Scrub Typhus is associated with perivasculitis, an inflammation of the tiny blood vessels. O. tsutsugamushi induces immune cell phagocytosis and then escapes the phagosome. Scrub typhus can spread through endothelial cells and macrophages to many organs, culminating in the development of lethal consequences.

Diagnosis

Scrub typhus may be identified in the laboratory using the following methods:

1. Organism isolation
2. Serology
3. Molecular diagnostics (PCR)

Numerous serological tests such as the Weil-Felix Test (WFT), indirect immunofluorescence (IIF), and enzyme-linked immunosorbent assay (ELISA) are presently available for the identification of rickettsial disorders. Although several approaches have been successfully utilised for rickettsial serodiagnosis, only a select handful are routinely employed by the majority of laboratories. A BSL-3 laboratory is not necessary to conduct serological testing.

ELISA (Enzyme-Linked Immunosorbent Assay): ELISA methods, particularly immunoglobulin M (IgM) capture assays, are arguably the most sensitive tests available for rickettsial diagnosis, and the presence of IgM antibodies indicates recent rickettsial disease infection. Towards the conclusion of the first week following infection with O. tsutsugamushi, a considerable IgM antibody titer is detected, whereas IgG antibodies develop at the end of the second week.

Molecular diagnostics (PCR): Blood is collected in tubes containing EDTA or sodium citrate for PCR. However, blood clots, whole blood, or serum can also be utilised to identify O. tsutsugamushi, R. rickettsii, R. typhi, and R. prowazekii organisms using a polymerase chain reaction (PCR).

Clinical characteristics

Scrub typhus patients may present early or late in the disease's course. Inoculation through chigger bites is frequently painless and unnoticeable. At the site of infection, a tiny, painless papule develops and gradually enlarges. A central necrosis region develops, followed by the production of eschars. At the onset of the fevers, the eschar (if present) is well formed, which may prompt the patient to seek medical assistance.

The incubation period is between 6 and 20 days (average, 10 days). Individuals may get headaches, shivering chills, lymphadenopathy, conjunctival infection, fever, anorexia, and overall lethargy following infection. The fever is frequently between 40 and 40.5°C (104 and 105°F).

Considerations for certain treatment interventions

If scrub typhus is suspected in patients with COVID, Doxycycline (200 mg twice daily in two split doses for 7 days) or Azithromycin (500 mg once a day for 5 days) should be provided. Individual issues should be managed according to established guidelines.

This article is part of our new series on managing COVID-19 coinfections. Stay tuned for a new update every week. To read the previous parts, click COVID-19 & seasonal illness- Protocol for determining co-infection, Managing dengue with COVID-19: Clinical considerations, COVID-19 + Influenza/bacterial co-infection, Malaria and COVID-19 co-infection: Management guidelines & COVID-19 & leptospirosis: How should you treat?