Usefulness of Sd30 in the diagnosis of arthritis of filarial origin.

common clinical manifestations like acute adenolymphangitis and chronic lymphoedema. But a number of other occult manifestations like asthmatic bronchitis, pulmonary eosinophilia, recurrent URI, pneumonia, pain in abdomen and mono-arthritis of filarial origin in filarial endemic areas remain undiagnosed because of lack of suitable diagnostic tool1. The present study has identified Sd30 (Sd—Setaria digitata, 30 MW-30 kDa), an allergenic fraction purified from Setaria digitata (a cattle filarial parasite) that can detect the antifilarial (Wuchereria bancrofti) antibodies (IgM and IgG4) produced during the acute/chronic manifestation of extra lymphatic pathology like arthritis caused by W. bancrofti infection in individuals residing in filaria endemic regions. The study was conducted at a Rheumatology Clinic, situated at Bhubaneswar, the capital city of Odisha, India. Total 80 arthritis patients from Khurda district, a W. bancrofti endemic region2 and 20 arthritis patients from filarial non-endemic region attending the clinic for treatment were enrolled in this study. These non-filaria endemic arthritis subjects were considered as a control group. Informed consent was obtained from the patients. The Institutional Ethical Committee has approved the study. All the patients had evidence of single joint inflammation (monoarticular arthritis) and redness over the infected joint. Filarial symptom like lymphangitis-axillary/lymphadenopathy-inguinal was also observed in a number of patients. Patients were treated with standard dose of diethyalcarbamazine (DEC), antibiotics and anti-inflammatory drugs as per the necessity of the patients. The presence of circulating filarial antigen, filarial specific antibodies and pro-inflammatory cytokines were examined in blood and synovial fluid. Different haematological parameters like haemoglobin level, total WBC count (TWBC), eosinophils percentage, absolute eosinophils count (AEC), erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) were examined. The Sd-30 antigen (MW-30 kDa) purified in our laboratory3 from Setaria digitata was used to determine the filarial specific antibodies (IgG, IgM and IgG4) levels by ELISA4. Presence of circulating filarial antigen was detected both in serum and in synovial fluid using Og4C3 ELISA kit (Trop Bio, Australia)5. The antigen unit 100 was used as a cut-off value for identification of antigenemia as per the manufacturer’s instruction. The pro-inflammatory cytokines such as interferon (IFN)-γ, interleukin (IL)-2 and interleukin (IL)-6 levels were measured by ELISA kit both in serum and synovial fluid. Antibody unit and O.D. value of each individual was plotted in the graph. Statistical analyses of the data were performed by using Graph Pad Prism (Version 5.01). Data were expressed as mean ± S.D. (Standard deviation). Significance level was determined by Student’s t-test. The patients were categorized into two groups depending on the presence of circulating filarial antigen (CFA) in serum or in synovial fluid. The individuals without detectable circulating filarial antigen in serum or synovial fluid were designated as CFA– (CFA negative) group and with circulating filarial antigen either in serum or in synovial fluid were designated as CFA+ (CFA positive) group. The filaria non-endemic arthritis patients were CFA–. Initially, the patients were treated with DEC (6 mg/kg body weight) for six days. All the CFA+ arthritis patients and some CFA– patients were found to respond positively and the symptoms (pain, swelling of the joint, fever and filarial symptoms) were subsided after five days of treatment and subsequently the treatment was continued up to 12 days. Complete recovery was observed after 10 days of treatment. But majority of the CFA– patients (either from filaria endemic region or from filaria non-endemic region) did not respond to DEC till Day 5 (Table 1). Therefore, these patients were treated with doxycycline (Standard dose) and NSAID (non-steroid anti-inflammatory drug) from Day 6 onward and were followed-up. The levels of anti-filarial antibodies (IgG, IgM and IgG4) to filarial antigen (Sd30) in both serum and synovial fluid are shown in Fig. 1. The representative dot plot depicts the antibody level of each individual. The J Vector Borne Dis 51, December 2014, pp. 345–348