Occurrence of Orientia tsutsugamushi, the Etiological Agent of Scrub Typhus in Animal Hosts and Mite Vectors in Areas Reporting Human Cases of Acute Encephalitis Syndrome in the Gorakhpur Region of Uttar Pradesh, India

Abstract

Outbreaks of acute encephalitis syndrome (AES) with high fatality and disability, are reported every year in the Gorakhpur region of Uttar Pradesh, India, with the etiology of >60% of the cases being attributed to scrub typhus. In the present study, the prevalence of Orientia tsutsugamushi, the etiological agent of scrub typhus, was investigated among animal hosts and their ectoparasitic trombiculid mites prevalent in AES-reported areas of Gorakhpur. A total of 154 rodents/shrews were collected using 777 Sherman traps set in 12 study villages, and the overall trap rate was 19.8%. In total, 2726 trombiculid mites belonging to 12 species were collected from 154 rodents/shrews trapped. The shrew mouse Suncus murinus was the predominant animal species (78.6%) collected. The principal vector mite Leptotrombidium deliense was the predominant species (82.7%), and its index was 14.6 per animal. Of 114 rodent/shrew sera samples screened through the Weil-Felix test, 57% were positive for antibodies against O. tsutsugamushi. Of 128 blood samples tested by polymerase chain reaction (PCR), one rodent sample was positive for the gene encoding 56 kDa protein and 25 for 60 kDa. Among 2726 mite samples tested as 315 pools through nested PCR, seven pools were positive for 56 kDa gene. Phylogenetic analysis confirmed circulation of Gilliam, Karp, and TA678 serotypes of O. tsutsugamushi in Gorakhpur. The study clearly demonstrated natural infection of O. tsutsugamushi in both small-animal hosts and vector mites in the AES-reporting villages of Gorakhpur, which confirms transmission of the scrub typhus pathogen in this region. The high infestation rate of L. deliense with O. tsutsugamushi infection indicates that the people living in the rural villages of Gorakhpur are at risk of infection with scrub typhus, which might lead to AES.

Genetic diversity of Orientia tsutsugamushi strains from patients in north India

“…Jain et al in a recent study from north India also reported a predominance of Gilliam-like strains (Jain et al, 2018b). Studies from small animals and mites from central India have also found that Karp and Gilliam predominate (Sadanandane et al, 2018).…”

Investigations of seasonal outbreaks of acute encephalitis syndrome due to Orientia tsutsugamushi in Gorakhpur region, India

“…More than 80 per cent trapped shrew/rodent were infested with trombiculid mites, with Leptotrombidium deliense Walch as the predominant species. The overall chigger index, defined as the proportion of shrews/rodents having trombiculid mite infestation, was highest for S. murinus (21.3%) 18 .…”

“…Although the clinical and laboratory findings among AES and AFI patients indicated the role of O. tsutsugamushi infection, evidence of the presence of the pathogen in animal hosts and vector mites was considered confirmatory to its transmission to humans. A cross-sectional survey of trombiculid mites was carried out during July and October 2015, in randomly selected villages in Gorakhpur with recent report of AES cases 18 . In the selected villages Sherman live traps were set in peri-domestic areas to catch rodents/shrews.…”

“…Molecular diagnosis of the scrub typhus was targeted for two different gene fragments, groEL and 56 kDa type-specific antigen (TSA) of O. tsutsugamushi , by conventional PCR and nested PCR, respectively for rodent/shrew blood samples. Detection of gene encoding 56 kDa protein, which amplifies 483 bp segments, was carried out by nested PCR for mite samples 18 .…”

“…Phylogenetic analysis confirmed circulation of Gilliam, Karp, and TA678 serotypes of O. tsutsugamushi in Gorakhpur. This study provided information on the relative abundance of small animal hosts, chigger mite vectors, and the prevalence of the scrub typhus pathogen, O. tsutsugamushi , in the animal and vector hosts 18 .…”