Antibodies to respiratory syncitial virus in a normal community in Chandigarh area, northern India*

Bull. Org. mond. Santa 1971. 45, 143-145 Bull. Wld Hlth Org. Antibodies to Respiratory Syncytial Virus in a Normal Community in Chandigarh Area, Northern India * S. C. AGARWAL,1 R. C. MAHAJAN, J. N. S. BARDOLOI, & N. K. GANGULY A survey for the presence ofrespiratory syncytial (RS) virus antibodies has been carried out in 346 sera from a healthy community in northern India. The results showed that 19.6 % ofthe sera were positive and hada titre of16 or more. The higher titres were observed more frequently in the younger age groups. There is, therefore, serological evidence for the occurrence of RS virus infection in India. Respiratory syncytial virus infection is widely distributed. It is commonly associated with lower respiratory tract illness among infants and children. The common illnesses are bronchiolitis, broncho- pneumonia, and croup. There are reports from different parts of the world concerning the isolation of this virus (Chanock et al., 1957; Peacock & Clarke, 1961; Brukova & Samankova, 1963; Parrot, 1963; Barkovich, 1964; Berglund et al., 1965; Spence et al., 1968). Doggett (1965) made a comprehensive review of serological evidence of infection with respiratory syncytial virus in different parts of th. world, including India. Doggett tested only 15 sera from India and there is no other record of serological evidence for the prevalence of respiratory syncytial virus infection in this country. Hence this study was undertaken (1) to study the incidence of inapparent infections and (2) to find out the prevalence and recurrence of infection in different age groups. MATERIALS AND METHODS Sera A total of 346 sera was studied. These were collect- ed from a wide spectrum of the population including office personnel, laboratory technicians, blood donors, and medical staff. The sera from children were collected mainly from those coming to the outdoor clinic for minor ailments or admitted to hospital with any illness other than illness of the * From the Department of Microbiology, Post Graduate Institute of Medical Education and Research, Chandigarh, India. 1 Present address: Professor and Head, Department of Microbiology, JIPMER, Pondicherry-6, India. respiratory tract. The ages of the persons from whom sera were collected varied from less than 1 year to approximately 70 years. Complement-fixing antigen The Long strain of respiratory syncytial virus was used in the preparation of complement-fixing antigen: it was obtained from American type-culture collection, Rockville, USA. The Long strain of respiratory syncytial virus was inoculated into rhesus monkey kidney tissue culture tubes. The cultures were maintained on Eagle's basal medium with 2% rabbit serum and 50 ,ug of streptomycin per ml, 50 IU of penicillin per ml, and 2.5 ,tg of amphote- ricin B per ml. Cytopathic changes characteristic of respiratory syncytial virus appeared in 36-48 hours. The tissue-culture fluids were harvested and were then frozen and thawed 3-4 times, and cen- trifuged at 2 500 rev/min for 15 min to remove all debris. The supematent fluid contained the viral antigen: this antigen was titrated in a checker board test with rabbit immune serum against the Long strain. Complement-fixation test All the sera were inactivated at 56°C for 30 min. Tests were done using 0.1-ml volumes of sera and two minimal haemolytic doses of fresh guinea-pig complement: 8 units of antigen and 2 units of complement were added to the serum. This was allowed to fix by incubation overnight at 4°C. On the following day sensitized sheep red blood cells were added and the results were recorded. 2712 - 143- S. C. AGARWAL AND OTHERS RESULTS Altogether 346 sera were tested for the presence of complement-fixing antibodies to respiratory syncytial (RS) virus. The results are shown in Table 1 and Fig. 1. It was found that 62.4% of the sera had little or no antibody; 17.9% showed an RS anti- body titre of 4 or 8; 19.6% had titres of 16 or more; and 14.4% had titres of 32 or more. Of the latter group, titres as high as 64 and 128 or more were found in 6.4% and 4.0% of the sera, respectively. These results indicated that the population under study had been previously infected by RS virus. Table I and Fig. 1 also show the distribution of RS antibody in different age groups. The proportion of sera showing no significant antibody ranged from 59.7% to 67.6%. An RS antibody titre of 4-8 was found in 14.0-24.3% of the sera and a titre of 4-16 Table 1. Distribution of complement-fixing antibody to respiratory syncytial (RS) virus among different age groups Age group (years) Total no. Percentage Antibody titre of sera of total 0-9 10-19 20-29 30-39 >40 of s sera 1 21 24 77 44 50 216 62.4 4 5 5 10 14 10 44 12.7 8 1 2 8 4 3 18 5.2 16 1 1 9 4 3 18 5.2 32 0 1 6 3 4 14 4.0 64 3 13 4 2 22 6.4 >128 1 4 6 1 2 14 4.0 No. of sera in each age group 32 37 129 74 74 346 100.0 70j60 ~50 3: 40 co 30 w 20 co co w 10 0-9 10-19 20-29 30(-a39 4O 0 Age-group (years)wo1o1 Fig. 1. Percentage distribution of complement-fixing antibody to respiratory syncytial virus by age group (black: titre <4; heavy shading: titre 4-8; light shading: titre >16.) 144 ANTIBODIES TO RS VIRUS IN CHANDIGARH, INDIA 145 in 20.9-29.7% of the sera. Significantly high titres of 16 or more, were found in 14.9-26.4% of the sera and titres of 32 or more in 10.8-19.4% of the sera. Higher proportions of antibody titres of 64 and 128 or more were found in sera from the younger age groups: these titres were found in 12.5% of the sera from the 0-9-year age group, 10.8% of those from the 10-19-year age group, and 14.7% of those from the 20-29-year age group but were found in only 6.8% of those from the 30-39-year age group and in 5.4% of those from persons aged 40 years or more. DISCUSSION The above results and the presence of significantly high titres of RS virus antibody in sera show that at least 20% of the population had had previous contact with the RS virus. The presence of RS virus antibody at a titre of 16 or more in 15.5% of sera from the 0-9-year age group indicates that infection probably begins at an early age. In this age group, 9.3% of the sera had a titre of 64, and 3.1 % had titres as high as 128 or more. The antibody persisted in nearly the same percentage of the population in the 10-19-year age group. There was, however, a significant increase in the number of sera showing raised titres (16 or more) in the 20-29-year age group. It is difficult to say whether this was due to reinfection. Beyond the age of40 years, the relative proportion of positive sera is lower and it appears that the infection subsides. It is interesting to note that the frequency of RS virus complement-fixing antibody is the same in a tropical country such as India and in countries with cold climates where similar studies have also been carried out. R]SUMt ANTICORPS POUR LE VIRUS SYNCYTIAL DES VOIES RESPIRATOIRES DANS UN GROUPE DE PERSONNES BIEN PORTANTES DE LA REGION DE CHANDIGARH (INDE SEPTENTRIONALE) On a recherch6 par la reaction de fixation du comple- ment la presence d'anticorps dirig6s contre le virus syncytial des voies respiratoires (virus RS) dans les serums pr6leves chez 346 sujets bien portants, ages de 1 a 70 ans, dans le nord de l'Inde. Des titres d'anticorps de 16 et plus ont ete trouves dans 19,6% des echantillons, la proportion des s6rums de titres 64 et 128 6tant respec- tivement de 6,4% et 4%. Les fortes teneurs en anti- corps ont W d6cel6es surtout dans les groupes d'age inf6rieurs. Cette enquete s6rologique limit6e apporte la preuve de la circulation du virus RS dans le nord de l'Inde. REFERENCES Barkovich, S. (1964) Pediatrics, 34, 753 Berglund, B., Vihma, L. & Wickstrom, J. (1965) Amer. J. Epidem., 81, 271 Brukova, M. & Samankova, L. (1963) es Epidem., 12, 44 Chanock, R. M., Roisman, B. & Mayers, R. (1957) Amer. J. Hyg., 66, 281 Doggett, J. E. (1965) Bull. Wid Hlth Org., 32, 849 Peacock, 0. B. & Clarke, S. K. R. (1961) Lancet, 2, 466 Spence, L. & Barratt, N. (1968) Amer. J. Epidem., 88, 257