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Gorakhpur division consisting of Gorakhpur and neighboring districts Deoria, Kushinagar and Maharajganj in Uttar Pradesh, India, have been witnessing seasonal outbreaks of acute encephalitis syndrome (AES) among children for the last three decades. Investigations conducted during 2005 identified Japanese encephalitis (JE) virus as an aetiology of AES. With the introduction of JE vaccination and other control strategies, the incidence of JE in the region declined, however, outbreaks of acute febrile illness with neurological manifestations continued to occur. Subsequent investigations identified Orientia tsutsugamushi, as the major aetiology of AES outbreaks in the region. This review details clinical, epidemiological, animal and entomological investigations conducted for AES due to O. tsutsugamushi during 2015 and 2017 in Gorakhpur region. Surveillance of acute febrile illness among children attending peripheral health facilities identified scrub typhus as an important aetiology of febrile illness during monsoon and post-monsoon months. Population-based serosurveys indicated high endemicity of scrub typhus. Entomological studies demonstrated natural infection of O. tsutsugamushi in small animal hosts and vector mites. Children acquired this infection through recent exposure to outdoor environment, while playing, or visiting fields or defecating in open fields. A few of the children with scrub typhus progress to develop CNS manifestations. Hence, early administration of appropriate antibiotics is crucial in preventing progression of AFI due to scrub typhus to AES. The investigations conducted by the multi-disciplinary team helped understand the transmission dynamics of scrub typhus in Gorakhpur division and recommend strategies for its control., Competing Interests: None

Seasonal outbreaks of acute encephalitis syndrome (AES) with high case fatality have been occurring in Gorakhpur division in Eastern Uttar Pradesh, India, for more than three decades. Japanese encephalitis virus (JEV) accounted for <10% of AES cases, while the etiology of the remaining cases remained largely unknown. Investigations conducted during the 2014 and 2015 outbreaks indicated Orientia tsutsugamushi (Haruo Hayashi 1920) (Norio Ogata 1929) Tamura et al. 1995 (Rickettsiales: Rickettsiaceae) as the etiology in about 60% of AES cases. Hospital-based surveillance studies indicated that about one-fifth of the patients with acute febrile illness were due to scrub typhus. Further studies are required to identify the etiology of about a third of AES cases that test negative for scrub typhus, JEV, or dengue.

Seasonal outbreaks of acute encephalitis syndrome (AES) with high mortality occur every year in Gorakhpur region of Uttar Pradesh, India. Earlier studies indicated the role of scrub typhus as the important etiology of AES in the region. AES cases were hospitalized late in the course of their illness. We established surveillance for acute febrile illness (AFI) (fever ≥ 4 days duration) in peripheral health facilities in Gorakhpur district to understand the relative contribution of scrub typhus. Of the 224 patients enrolled during the 3-month period corresponding to the peak of AES cases in the region, about one-fifth had immunoglobulin M (IgM) antibodies against Orientia tsutsugamushi . Dengue and leptospira accounted for 8% and 3% of febrile illness cases. Treating patients with AFI attending the peripheral health facilities with doxycycline could prevent development of AES and thereby reduce deaths due to AES in Gorakhpur region.