Scrub typhus is caused by Orientia tsutsugamushi, (‘tsutsuga’ means something small and dangerous and
‘mushi’ means insect/mite/creature) which circulates mainly between human and rodents. Clinical signs and symptoms include febrile condition, headache, eschar, lymphadenopathy, muscular pain and gastrointestinal dis- orders which in severe and untreated case may end into fa- tal multiple organ failure1–7. The observation of the eschar is often missed and other symptoms of the disease are not characteristic thus posing the problem of delayed diagno- sis by the clinician. Although, scrub typhus is known since 1889 in Japan, the severe epidemics of scrub typhus in Burma (Myanmar) and Ceylon (Sri Lanka) during World War II intensified the interest of studying about this dis- ease8. Scrub typhus is endemic in a region called ‘tsutsu- gamushi triangle’ which extends from northern Japan and far-eastern Russia in the north, to the territories around the Solomon Sea into northern Australia in the south and to Pakistan and Afghanistan in the west1–2. In India, scrub typhus was first reported from Assam and West Bengal states during World War II9. The disease is being reported in many endemic pockets of different states of India such as Maharashtra, Tamil Nadu, Karnataka, Kerala, Jammu and Kashmir, Uttarakhand, Himachal Pradesh, Rajasthan, West Bengal, Assam, Arunachal Pradesh, Sikkim, Naga- land and Meghalaya1–6.
Vaccination against this scourge faces challeng- ing obstacles such as extensive antigenic diversity and short duration of immune protection following immunity stimulated by naturally acquired scrub typhus infection.
Moreover, immunity to the homologous strain wanes over a period of few years7. In the present situation, early diag- nosis and chemotherapy is the only choice for combating scrub typhus infection and reducing associated mortality.
Diagnosis of scrub typhus is carried out mainly by sero- logical assays, though in recent years, there are specific molecular detection techniques employing amplification of different target genes by polymerase chain reaction.
The immunofluorescence assay (IFA) is considered as
‘gold standard’ for diagnosing rickettsial infections but faces certain demerits like its cost-effectiveness in devel- oping countries and technical expertness. One of the most widely used serological assay, Weil-Felix test suffers from poor sensitivity and specificity. Scrub typhus ELISA, which uses O. tsutsugamushi recombinant p56 kD type- specific antigen of Karp, Kato, Gilliam and TA716 strains has > 90% sensitivity and specificity for detecting specific antibodies10–11. However, the samples are usually exam- ined multiple times for ELISA test thereby causing delay in diagnosis. On the contrary, rapid detection in immuno- chromatographic test format can identify a single sample in short span of time.
The present study was carried out to know the cur- rent status of the prevalence of scrub typhus in Mizoram from clinically suspected patients who were admitted to Synod Hospital, Aizawl, Mizoram by rapid-ICT test kit. A cross-sectional study was conducted from October 2014 to December 2016 on serum samples of patients with un- differentiated fever from different parts of Mizoram ad- mitted to the Synod Hospital, Mizoram. The samples were examined for detection of anti-OrientiaIgM antibody in rapid-ICT test having sensitivity of 98.6% and specific- ity of 98.2% (ImmuneMed scrub typhus rapid test kit, South Korea)12. Clinical samples were collected after tak- ing informed consent from the patients.
A total of 4081 sera samples were examined for the presence of anti-Orientia IgM antibody in the human sub- jects. The result revealed that 6.9% (n = 283) samples were positive in the test kit, irrespective of age and gender. The percentage of seropositivity was higher during the win- ter (November–February) at 13.5% (154/1141) followed by autumn (September–October) at 10.9% (141/1287).
In summer and spring seasons the percentages were comparatively lower at levels of 4.8 and 5.5%, respec- tively. Age wise comparison of the prevalence indicated that 21–30 yr age group were most affected (prevalence
Scrub typhus in Mizoram, India
H. Lalrinkima
1, R. Lalremruata
2, C. Lalchhandama
3, Lalthansanga Khiangte
4, Freddy H.
Siamthara
1, C. Lalnunpuia
1, S.K. Borthakur
1& Gautam Patra
11Department of Parasitology, College of Veterinary Sciences and Animal Husbandry, Central Agricultural University, Aizawl; 2Department of Microbiology, Synod Hospital, Aizawl; 3Department of Toxicology, 4Department of Animal Genetics and Breeding, College of Veterinary Sciences and Animal Husbandry, Central Agricultural University, Aizawl, India
Key words IgM rapid ICT-test kit; India; Mizoram; Scrub typhus; seroprevalence J Vector Borne Dis 54, December 2017, pp. 369–371
J Vector Borne Dis 54, December 2017 370
23.7%) followed by 31–40 yr age group (20.8%). The age groups of 1–10 and 41–50 yr showed least seropositivity (9.2% each). The seropositivity for the age groups, 11–20, 51–60 and ≥60 yr was in between these two extremes, i.e. 13.4, 11.7 and 12.0%, respectively (Fig. 1). The gender-wise comparison showed that males (56.2%) were having higher prevalence rate than females (43.8%), ir- respective of age and season (Table 1).
The overall prevalence of 6.9% in the present study was found to be lower in comparison to the earlier re- ports from different parts of India. The seropositivity of the results reported from the neighbouring states of north- eastern India, i.e. Nagaland, Meghalaya and Arunachal Pradesh by indirect ELISA were 36.55, 53.33 and 40%, respectively6, 13. The comparatively higher incidence of scrub typhus during autumn (11%) and winter (13.5%) in the present study may be due to increased human activities in the agricultural fields and bushes during these seasons, as there is relatively moderate climate in sub-tropical forests and accumulation of post-harvest paddy straw at- tracts rodent population, both contributing as deciding factors for scrub typhus transmission. Similar pattern of the disease occurrence has been reported from southern states of India where higher incidence was recorded in colder season of the year4–5; on the contrary, northern India and other southeast Asian countries encountered the
disease at highest rate during rainy season of the year4,12–13. The demographic characteristic in the seropositivity of scrub typhus varied with age and gender. The study re- sults showed higher seropositivity in two age groups, viz.
21–30 and 31–40 yr; affecting predominantly males cor- roborating with earlier reports3, 14–15. The higher outdoor and agricultural activities by males could be the reason of higher seropositivity of scrub typhus in this gender.
In India, the first case of scrub typhus was reported from Assam and West Bengal9 in the year 1945; and the re-emergence of this scourge was reported in 2010 after a gap of 65 yr17. Since then, there are little documentations about the incidences and seropositivity of scrub typhus from northeast India7, 11. The subtropical rain forest of Northeast India is conducive for vector propagation and at the same time is vulnerable to climate change18. There has been considerable debate as to whether global risk from vector-borne diseases will be impacted by climate change; however, this debate has mostly ignored the bio- logical diversity of vectors and vector-borne diseases19. Therefore, detailed studies on the correlation between the recent resurgence of scrub typhus in northeastern India and the climate change is warranted.
In conclusion, this study briefly describes the sero- prevalence of scrub typhus in Mizoram state of north- eastern India, where during post-monsoon autumn and winter seasons the increased human activities in bushes and agricultural fields have impacted upon the higher rate of scrub typhus incidences. Preventive measures like protective clothings and application of insect repellents along with public awareness about the disease transmis- sion dynamics are important for reducing the disease prevalence.
Conflict of interest: None to declare.
Ethical statement
The study does not involve ethical issues.
ACKNOWLEDGEMENTS
The authors sincerely acknowledge the Director, Synod Hospital, Aizawl for providing necessary data and the Dean, College of Veterinary Sciences and Animal Husbandry, Selesih, Aizawl for providing necessary facilities.
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Correspondence to: Dr H. Lalrinkima, Department of Parasitology, College of Veterinary Sciences & Animal Husbandry, Central Agricultural University, Aizawl, Mizoram–796 014, India.
E-mail: [email protected]
Received: 26 July 2017 Accepted in revised form: 15 November 2017
