The 2001 dengue epidemic in Chennai.

Dengue is emerging as a serious public health problem in Tamil Nadu. The present surveillance system is unlikely to generate proper information on the epidemiology of the disease, which is essential for planning and development of relevant control/preventive measures against dengue. OBJECTIVE: Between November 2001 and January 2002, a descriptive study was undertaken on children with clinical dengue attending Kanchi Kamakoti Child Trust Hospital (KKCTH, a major private referral pediatric hospital in Tamil Nadu, India) to define the magnitude of dengue burden, the natural history of this disease in terms of clinical presentation, and outcome of the infections in hospitalized children (< 15) with clinical dengue. METHODS: The sera collected from patients analyzed for dengue specific IgM and IgG antibodies by IgM, IgG antibody capture enzyme linked immunosorbent assay (ELISA) using alternatively two commercial kits. World Health Organization clinical case definition was adopted to categorize the dengue confirmed children. RESULTS: Dengue was diagnosed in 74.5% (143) of the 192 hospitalized children with clinical dengue. A considerable proportion (20%) of the total dengue infections were constituted by infants less than 1 yr of age. DF [dengue fever], DHF [dengue hemorrhagic fever] and DSS [dengue shock syndrome] were diagnosed in 65%, 11.2% and 23.8% of 143 dengue confirmed patients respectively. Though severe dengue (DSS + DHF) was present in 35% of the patients, the mortality rate was low during the study period due to timely diagnosis and clinical management of the patients. CONCLUSION: In developing countries like India, building of laboratory capacity for diagnosis and combat-mode ready preparedness for the management of dengue cases in emergency situation may reduce dengue-related mortality. This can be achieved in a wider scale through an integrated approach through the community, professionals and the public health departments.

First time detection of Japanese encephalitis virus antigen in dry and unpreserved mosquito Culex tritaeniorhynchus Giles, 1901, from Karnal district of Haryana state of India.

Japanese encephalitis virus (JEV) antigen has been detected by antigen capture enzyme linked immunosorbentassay (ELISA) in dry specimens of the mosquito Culex tritaeniorhynchus Giles, 1901, collected from Karnal district of Haryana state in northern India. These mosquitoes were stored in dry condition for 20 months, at room temperature, before processing. The procedure of detecting JEV infection in long time stored, dry vector mosquitoes, has important application in the surveillance of Japanese encephalitis.

Cross-resistance to Bacillus sphaericus strains in Culex quinquefasciatus resistant to B. sphaericus 1593M.

Bacillus sphaericus 1593M resistant larvae of Culex quinquefasciatus were reared in the laboratory since 1995. Resistance in the larvae was monitored by subjecting selection pressure using B. sphaericus 1593M at every generation. Bioassays were conducted with different strains of B. sphaericus (Bs 2297, Bs 2362 and Bs IAB 59) and confirmed cross-resistance in the present study. The level ranged between 27.3 to 18.2 fold in comparison with susceptible larvae. But Bacillus thuringiensis var israelensis strains (Bti PG14 and Bti 426) did not show any cross-resistance in the larvae and it emphasized a need to study the mode of action of B. sphaericus toxin that induces cross-resistance in the larval strain.

Immune responses to chloroquine--sensitive and resistant populations of Plasmodium berghei in mice.

In order to elucidate the role of the host as a factor in the spread of chloroquine resistance, a study of the host's immune responses in chloroquine resistant (cqr) and chloroquine sensitive (cqs) Plasmodial infections is essential. Course of the infection and the nature of immune responses in mice infected with chloroquine resistant (R) and chloroquine sensitive (S) strains of Plasmodium berghei were compared. Crude parasite antigen activated T cells from both the groups of mice (R and S) and the parasite specific antibodies were detected in the sera of both the groups. The differences in immune responses between the control (uninfected) and infected mice were found to be significant. However, humoral and in vitro cellular responses obtained with T cells from chloroquine resistant P. berghei primed mice was lower in comparison with the responses obtained with T cells from the sensitive infections. Our studies therefore suggest that immunosuppression to parasite antigen is seen in mice primed with chloroquine resistant P. berghei, which may play a role in the development of resistance.

T cell immunity in malaria.

Immunity to malaria is a complex process. In malaria endemic areas, sustained clinical immunity develops gradually. Protective immunity to malaria comprises both antibody-dependent and antibody-independent effector mechanisms. Although, the relative roles of B and T cells differ in different malaria systems and different stages of the parasite, T cells are essential for the induction and maintenance of immunity against malaria. T cell-derived soluble factors are believed to be important mediators of cellular effector mechanisms. The efficacy of an antigen as a malaria vaccine depends to a great extent on the T cell recognition sites and the nature of the responses induced by these determinants. In order to select suitable epitopes in an immunogen, an understanding of the definition of antigenic sites recognized by T cells and characterization of the nature of the T cell responses induced in malaria endemic populations is important.

Humoral immune responses to the Plasmodium falciparum antigen Pf155 RESA in adults with differential clinical conditions from an Indian zone where malaria is endemic.

Ring infected erythrocyte surface antigen of Plasmodium falciparum (Pf155/RESA) has been considered as a vaccine candidate. However, the relative immunogenicity of this antigen has not been studied in Indian populations. Pf155/RESA was investigated for its immunogenicity by studying humoral immune responses against Pf155/RESA and Pf155/RESA derived peptides (P1, P2 representing immunodominant epitopes from the 3' and P3 from the 5' repeat regions) by erythrocyte membrane immunofluorescence (EMIF) assay and by enzyme linked immunosorbent assay (ELISA) in P. falciparum primed donors living in hyperendemic malarious areas (Orissa State, India) where P. falciparum infections are highly prevalent. Subjects of different clinical status namely acute (A), clinically immune (CI) and acute with history of repeated P. falciparum infections (R) were included in this study. All the donors were seropositive against the crude antigen. There was considerable variation in the responses among the donors. While humoral responses in the plasmas against the P2 peptide (EENV)4 were significantly higher in magnitude and in frequency in the CI donors than in the A donors, no positive response was seen in the R donors. The responses to the peptides P1 (EENVEHDA)2 and P3 (DDEHVEEPTVA)2 were poor both in the A and in the CI groups. Whereas, most of the R donors were seropositive against the P3. The present results indicate that Pf155/RESA contains B cell epitopes which were recognized differently by the immune system of individuals living in malaria-hyperendemic areas of India who have been primed by natural infection. Our studies also suggest that in order to investigate the possible functional role of a given antigen, study of immune responses against the antigen in donors of different clinical status may be useful.