Scrub typhus or bush typhus or chigger – borne typhus is a leading cause of undifferentiated febrile illness caused by the intracellular gram negative bacteria orientia tsutsugamushi of family rickettsiaceae first isolated and identified in 1930 in japan. Iin countries like india, indonesia, thailand, nepal, sri lanka, maldives and myanmar, scrub typhus remains endemic. in india scrub typhus has been steadily increasing and is reported from almost all states in the last few years.

Epidemics have been reported from pondicherry, andhra pradesh and southern states, uttarakhand and other states in north india.

Urbanization and increased diversion of forest land for agricultural use and climate change have impacted the epidemiology, steering the disease transmission upward.

The vectors of scrub typhus are trombiculid mites of the genus leptotrombidium deliensis. these mites inhabit in the soil and shrubs or bushes where the microecosystem is favourable( mite islands).humans are infected when they are bitten by the mite larvae(chiggers).

The bite of amite leaves a characteristic eschar at the site of bite which gives a clinician some diagnostic finding but some times this finding may be missed and other signs and symptoms may be not specific to this disease leads to delayed diagnosis and treatment.

In this study we had collected some of the eschar findings with patient consent.

The incubation periodof this disease is 1-3weeks, patients develop a characteristic eschar at the site of the chigger bite, with regional lymphedenopathy and maculopapular rash. the disease sets in with fever, headache, muscle pain, nausea and vomiting.

Encephalitis and pneumonia may be seen in severe cases, other complications are acute kidney injury, hepatitis, acute respiratory distress syndrome, myocarditis and septic shock.

Systemic review on the burden of scrub typhus in india which is in the “tsutsugamushi triangle” (from tsutsuga meaning dangerous and mushi meaning insect or mite). this is found only in areas with a suitable climate, plenty of moisture, and scrub vegetation, revealed that scrub typhus accounts for at least 25.3% among individuals with acute undifferentiated febrile illness (aufi).

Despite being one of the commonest pathogens of the cause of such commonly encountered illness, it remains a neglected disease in terms of research and formulation of health care policies, due to the lack of proper laboratory confirmation tests, it remains a neglected disease in a developing country like india.failure of early diagnoses leads to morbidity and mortality in these patients, early antibiotic treatment can prevent this. hence, the present study was planned to understand the seroprevalence of scrub typhus among patients presenting with febrile illness.

The diagnostic tests for scrub typhus includes culture and serology.

culture requires biosafety cabinet iii, in available serological tests weil felix test is the one which is easy and cheap but the results are unreliable and it lacks sensitivity. other test available are indirect immunoflourescence test the gold standard test beyond affordability and need expertise to read the test results, the other one is elisa for detection of igm antibodies which has good specificity and sensitivity.

This study was carried out to know the seroprevalence of scrub typhus in clinically suspected cases.

clinical presentation of patients

clinical features                                 no of patients

• This study was prospective observational study, study performed at state vrdl at department of microbiology, guntur medical college/government general hospital, guntur from june 2023 to january 2024. Permission taken from institutional ethicsAll the patients attending the outpatient department and in patients suspected of pyrexia of unknown origin (puo) were included in the study.

     Exclusion criteria was confirmed cases for other febrile illnesses like malaria, typhoid, dengue,           

     chikungunya, leptospirosis.

Five ml of venous blood was collected in a plain vial without anticoagulant and serum was separated after centrifugation at 3,000 rpm for 5 min. this serum was used for further testing by elisa for igm antibodies.

Scrub typhus igm microlisa is designed for in vitro qualitative detection of scrub typhus igm antibodies in human serum or plasma and is used as a screening test for testing of collected blood samples suspected for scrub typhus infection.

Scrub typhus igm microlisa method

*Principle:* indirect elisa: specimens with igm antibodies to scrub typhus bind to coated antigen. after washing, hrp-conjugated anti-human igm binds. substrate solution develops color proportional to igm antibodies present.

• *Kit presentation:* 96 test

This elisa kit offers a comprehensive solution for qualitative detection of scrub typhus igm antibodies, with detailed instructions for proper handling and interpretation of results.

• Scrub typhus igm microlisa is designed for in vitro qualitative detection of scrub typhus igm antibodies in human serum or plasma and is used as a screening test for testing of collected blood samples suspected for scrub typhus infection.

 Principle:

• scrub typhus igm microlisa test is an enzyme immunoassay based on “indirect elisa”. recombinant protein

representing immunodominant epitopes of scrub typhus are coated onto microtiter wells.

• specimens and controls are added to the microtiter wells and igm antibodies to scrub typhus if present in the specimen, will bind to the specific scrub typhus antigen absorbed onto the surface of the wells.
• the plate is then washed to remove unbound

horseradish peroxidase (hrp) conjugated anti-human igm is added to each well. this conjugate will bind scrub typhus antigen-antibody complex present.

• finally substrate solution containing chromogen and hydrogen peroxide is added to the wells and
• A blue color will develop in proportion to the amount of scrub typhus igm antibodies present in the specimen. the color reaction is stopped by a stop solution. the enzyme substrate reaction is read by eia reader for absorbance at a wavelength of 450 nm along with 630 nm (reference filter).
• if the sample does not contain scrub typhus igm antibodies then enzyme conjugate will not bind and the solution in the wells will be either colourless or only a faint background colour develops.

Table no - 1

The above table showing total samples tested in the study period was 366,

Positives were 41 (11.2%) and negatives were 325(88.79%).

Table no - 2

The above table shows total positives were 41 (11.2%) out of 366 samples,out of 41 positives, males were 22(53.65%) and females were 19(46.34%)

Table no - 3

Age distribution:

This table shows out of 41 positive cases 78% of age group effected were below 20 years, followed by 34.14% were 41-60 yrs age group,12.1% were 21 to 40 yrs and 4.87% were 61 to 80yrs age group effected.

Scrub typhus or bush typhus or chigger – borne typhus is a leading cause of undifferentiated febrile illness caused by the intracellular gram negative bacteria orientia tsutsugamushi of family rickettsiaceae.

Out of 366 samples, 41(11.2%) samples were tested positive for scrub typhus and 325(88.79%) samples were negative. it was found that the prevalence in the andhra pradesh was 56% and 39% in the year 2011 and 2013 [14,15]

 Out of 41(11.2%) , males were 22(53.65%) and females were 19(46.34%).the age group showing high positivity in our study was below 20 years age group. in a study by v rajagopal et al., (vellore) the highest percentage was in 16-25 years [16]. ragini et al., found maximum cases of 31-40 age group in a study on febrile illness in uttharakhand [17].in our study mostly younger age group was effected due to their occupation and active age group.

 In our study the common symptoms presented are fever, vomiting, headache followed by rashes, respiratory symptoms, and on 7 patients characteristic eschar was noted.

Our study provides an evidence for the seropositivity of scrub typhus in this area. scrub typhus also one of the febrile illness which shoud be included in puo along with other like malaria , typhoid and other diseases. in our study elisa test shows good sensitivity and specificity, so elisa can be preferred to diagnose scrub typus if no other gold standard tests are available

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