Strong interferon-gamma mediated cellular immunity to scrub typhus demonstrated using a novel whole cell antigen ELISpot assay in rhesus macaques and humans
PLOS NEGLECTED TROPICAL DISEASES
Authors: Sumonwiriya, Manutsanun; Paris, Daniel H.; Sunyakumthorn, Piyanate; Anantatat, Tippawan; Jenjaroen, Kemajittra; Chumseng, Suchintana; Imerbsin, Rawiwan; Tanganuchitcharnchai, Ampai; Jintaworn, Suthatip; Blacksell, Stuart D.; Chowdhury, Fazle R.; Kronsteiner, Barbara; Teparrukkul, Prapit; Burke, Robin L.; Lombardini, Eric D.; Richards, Allen L.; Mason, Carl J.; Jones, James W.; Day, Nicholas P. J.; Dunachie, Susanna J.
Scrub typhus is a febrile infection caused by the obligate intracellular bacterium Orientia tsutsugamushi, which causes significant morbidity and mortality across the Asia-Pacific region. The control of this vector-borne disease is challenging due to humans being dead-end hosts, vertical maintenance of the pathogen in the vector itself, and a potentially large rodent reservoir of unclear significance, coupled with a lack of accurate diagnostic tests. Development of an effective vaccine is highly desirable. This however requires better characterization of the natural immune response of this neglected but important disease. Here we implement a novel IFN-.ELISpot assay as a tool for studying O. tsutsugamushi induced cellular immune responses in an experimental scrub typhus rhesus macaque model and human populations. Whole cell antigen for O. tsutsugamushi (OT-WCA) was prepared by heat inactivation of Karp-strain bacteria. Rhesus macaques were infected intradermally with O. tsutsugamushi. Freshly isolated peripheral blood mononuclear cells (PBMC) from infected (n = 10) and uninfected animals (n = 5) were stimulated with OT-WCA, and IFN-gamma secreting cells quantitated by ELISpot assay at five time points over 28 days. PBMC were then assayed from people in a scrub typhus-endemic region of Thailand (n = 105) and responses compared to those from a partially exposed population in a non-endemic region (n = 14), and to a naive population in UK (n = 12). Mean results at Day 0 prior to O. tsutsugamushi infection were 12 (95% CI 0-25) and 15 (2-27) spot-forming cells (SFC)/10(6) PBMC for infected and control macaques respectively. Strong O. tsutsugamushi-specific IFN-gamma responses were seen post infection, with ELISpot responses 20-fold higher than baseline at Day 7 (mean 235, 95% CI 200-270 SFC/10(6) PBMC), 105-fold higher at Day 14 (mean 1261, 95% CI 1,097-1,425 SFC/10(6) PBMC), 125-fold higher at Day 21 (mean 1,498, 95% CI 1,496-1,500 SFC/10(6) PBMC) and 118-fold higher at Day 28 (mean 1,416, 95% CI 1,306-1,527 SFC/10(6) PBMC). No significant change was found in the control group at any time point compared to baseline. Humans from a scrub typhus endemic region of Thailand had mean responses of 189 (95% CI 88-290) SFC/10(6) PBMC compared to mean responses of 40 (95% CI 9-71) SFC/10(6) PBMC in people from a non-endemic region and 3 (95% CI 0-7) SFC/10(6) PBMC in naive controls. In summary, this highly sensitive assay will enable field immunogenicity studies and further characterization of the host response to O. tsutsugamushi, and provides a link between human and animal models to accelerate vaccine development.
Serological evidence of spotted fever group rickettsiosis in and around Puducherry, south India-A three years study
JOURNAL OF VECTOR BORNE DISEASES
Authors: Stephen, Selvaraj; Ambroise, Stanley; Gunasekaran, Dhandapany; Hanifah, Mohammed; Sangeetha, Balakrishnan; Pradeep, Jothimani; Sarangapani, Kengamuthu
Background & objectives: Rickettsial diseases are important re-emerging infections that mostly go unnoticed or are misdiagnosed. Though few case reports of Indian tick typhus have been reported in Indian literature in the past 10 yr, prevalence surveys are few and far between. The objective of this research was to study the seroprevalence of spotted fever (SF) group rickettsiosis and its coinfection with scrub typhus (ST) in Puducherry region of south India, as these two diseases may show similar clinical presentations. Methods: During 2012-2015, paired sera of 320 febrile patients were examined for Rickettsia conorii IgM/IgG by ELISA and OX19 and OX2 agglutinins by Weil-Felix test. Additionally, patients were screened for ST IgM ELISA. Statistical analysis was performed for clinical and laboratory parameters in children and adults using Fisher's exact test and chi-square test with Yates correction. Results: Out of 320 patients, 142 (44.38%) had R. conorii IgM and/or IgG antibodies. Only IgM was present in 72 (22.5%) patients, while 36 patients were positive for IgG only and 34 were positive for both IgG and IgM. A total of 68 patients (21.25%) showed only OX19 and/or OX2 antibodies (titres >= 1 : 80). SF and ST coinfection was observed in 47 cases (14.69%). Interpretation & conclusion: Seroprevalence of SF in Puducherry was found to be quite high (44.38%). ST and SF coinfection was observed in 34.50% of the SG IgG positive patients, however, this require further evaluation by PCR to rule out cross-reaction or false positivity. At present ELISA seems to be an affordable alternative to highly subjective and technically demanding immunofluorescence assay (IFA) for serodiagnosis of SF.