Salivary Anti-50 kDa Antibodies as a Useful Biomarker for Diagnosis of Typhoid Fever

INTRODUCTION: Typhoid fever remains a scourge of humanity, especially in developing and under-developed countries due to poor sanitation and food hygiene. Diagnostic methods available for detection of this disease are not satisfactory due to a lack of sensitive, specific, rapid and convenient diagnostic test kits available in the market.

AIM: To evaluate the feasibility of a Dot-EIA method for Ig-class specific salivary antibody detection for diagnosis of typhoid fever.

MATERIALS AND METHODS: Paired saliva and serum samples were collected in the year 2010 from patients and normal volunteers in Hospital Universiti Sains Malaysia, Kelantan, Malaysia, which is endemic for typhoid fever. A total of 11 culture-confirmed typhoid fever patients, 43 non-typhoid fever patients and 53 normal human control subjects were evaluated for antibodies against a 50 kDa antigen specific for Salmonella Typhi using Dot-EIA.

RESULTS: Ig class-specific screening of the test samples showed a higher sensitivity for IgA (90.9%) compared to either IgG (72.7%) or IgM (72.7%) antibodies in saliva, but for serum, IgG (90.9%) had a higher degree of sensitivity compared to IgA (36.4%) and IgM (63.6%). Combining all isotypes (IgA, IgG or IgM), serum showed a higher sensitivity (100.0%) compared to saliva (90.9%). Also, the specificity for serum (100.0%) was much higher than saliva (85.4%).

CONCLUSION: Salivary IgA anti-50kDa antibody was found to be more suitable biomarker for routine screening, whereas serum IgG was more suitable for confirmatory test as it has higher specificity. Nevertheless, salivary IgA Dot-EIA is a convenient method for rapid testing, such as for Point-of-Care Diagnostics (POCD) and field epidemiological studies, due to its non-invasive nature and ease of use.