Scrub Typhus and its co-infection with Leptospirosis at a tertiary care hospital in Uttar Pradesh

Introduction

The vector-borne disease Scrub Typhus, the aetiological agent being the obligate intracellular bacterium Orientia tsutsugamushi, is transmitted to humans by the bite of the infected larval mite of genus Leptotrombidium. ¹ Gilliam, Karp, and Kato are the three primary prototype strains. ² The disease is characterized by an acute febrile illness with or without eschar formation at the site of inoculation. It can progress to encephalitis or acute respiratory distress syndrome. The disease, once considered to be underdiagnosed, has taken its place in the list of leading causes of Acute Encephalitis Syndrome (AES) ³ owing to improved diagnostic facilities, particularly in India. The fact that cases may also be increasing simultaneously cannot be ruled out. The positive side of the story is that the disease is still manageable with dapsone, with recent studies showing doxycycline resistance as a misconception.

Leptospirosis is another bacterial infectious disease caused by Leptospira interrogans and transmitted through animal (rodent, cat, pig, dog) urine. The disease, previously considered rare, is now being reported with increasing frequency. It is well characterized by hepato-renal dysfunction, meningitis, and respiratory distress apart from usual features including fever, headache, or myalgia. Various diagnostic methods include microscopic agglutination test, Enzyme-Linked Immunosorbent Assay (ELISA), and Polymerase Chain Reaction (PCR). Penicillin, doxycycline, and amoxicillin are the commonly prescribed antibiotic for this zoonotic infection.

Methods

Our study was conducted at the Department of Microbiology, King George's Medical University (KGMU) located at Lucknow, Uttar Pradesh, India. Subjects of all age groups were included. A total of 1743 blood samples collected from suspected patients with acute febrile illness were analyzed from Jan till Dec 2019. Data were collected retrospectively on cases of Scrub Typhus and their correlation with Leptospirosis in consecutive patients (both out- and in-patient) presenting to KGMU during the study period. Serological testing of Scrub Typhus was performed by the demonstration of IgM antibodies to 56 kDa antigen of O. tsutsugamushi, using a commercial kit IgM ELISA (Scrub Typhus Detect™, InBios International Inc., Seattle, Washington, USA). The cut-off used for the IgM ELISA was an optical density (OD) of 0.5. For the detection of anti-Leptospira IgM antibodies, a Panbio Leptospira IgM ELISA kit was used.

Results

Out of the total of 1743, 361 (20.7%) were clinically and microbiologically confirmed Scrub Typhus cases, aged between 8 months and 90 years and there was a slight predominance of the disease in men than women (M/F = 1.09: 1) as shown in Table 1. Maximum cases of Scrub Typhus were reported in the months of October-November as depicted in Figure 1.

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Figure 1.

Seasonal distribution of Scrub Typhus cases from Jan 2019 to December 2019.

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Table 1.

Age (years) and genderwise distribution of Scrub Typhus cases.

Age(yrs)		0–10	11–20	21–30	31–40	41–50	51–60	61–70	71–80	81–90
Gender (No. of cases)	Males (188)	15	51	34	29	29	14	10	5	1
	Females (173)	12	30	40	41	26	15	7	1	1
Total	361	27	81	74	70	55	29	17	6	2

We found 23 such samples in which anti-Leptospira, as well as anti-Orientia tsutsugamushi IgM antibodies, were detected when 275 samples were screened for both.

Discussion

Scrub Typhus as a cause of AES in endemic areas was found in c. 20% of cases ³ ; this neglected yet treatable disease should be considered, especially during the season of predominance. During the months of October-November, there is spurt in the growth of scrub vegetation that creates a favourable environment for the chigger mite population, whose bite brings the infection. ⁴ Our findings suggest that the disease is spreading widely in the community especially in the district of Uttar Pradesh; thus the battle against this disease will inevitably continue for some years to come. Co-infection of Scrub Typhus and Leptospirosis is increasingly being reported from different parts of the world. The highest distribution of Leptospirosis is in India, Brazil, Malaysia, and Thailand.^7-9 The mortality rate reaches 30% for both diseases if left untreated.⁷ A similar epidemiological pattern including shared risk factors such as outdoor activities, common seasonal spread and reservoir such as rodents, must highlight the possibility of this lethal combination.¹⁰