594 TRANSACTIONS OP THE ROYAL SOCIETY OF TROPICAL MEDICINE AND H~a~m,V0~.73,N0.5,1979

Arbovirus antibodies in the human population

of Hong Kong

B. K. JOHNSON,A. C. CHANAS,I?. GARDNER,D. I. H. SIMPSON Arbovirus Unit, London School of Hygiene and Tropical Medicine, Winches Farm Field Station, 395 Hatfield Road, St. Albans, Hem, England AND

K. F. SHORTRIDGE Department of Microbiology, Pathology Building, Queen Mary Hospital Compound, University of Hong Kong

Hong Kong lies within the latitudes and climatic zone in which a number of arthropod-borne viruses (arboviruses) are known or suspected of being endemic or enzootic, the most important being Japanese encephalitis (JE) virus. There have been sporadic human casesof JE in Hong Kong diagnosed on clinical and serological grounds (Dr. W. K. Chang, personal communication). In addition, serological studies have indicated the presence of JE exposure in pigs in Hong Kong (HIGGINS, 1970; Shortridge, unpublished data) and in cold-blooded animals from southern China (SHORTRIDGE ec al., 1974; 1975; 1977). Located to the north-west of the Philippines on the southern coast of China, Hong Kong is in a position where certain arboviruses from the temperate regions to the north, south-east Asian viruses from the west and, conceivably, arboviruses from the Australian region might occur. With the recent increase in the population of Hong Kong there has been considerable development of the rural New Territories which could result in the movement of people or domestic animals into localities which might be foci of arbovirus activity. These factors provided the background to the following study aimed at gathering information as a guide to prevalence of arboviruses in the area. A selection of 235 human sera, to be tested against several arbovirus antigens, was collected between 1973 and 1977 from out-patients attending a hospital in the New Territories. When possible, data on age, sex, occupation and illness was obtained. An additional 256 sera, to be tested only against JE antigen, were obtained from university students from urban Hong Kong. The sera. all containing 0.04% sodium azide were extracted by kaolin treatment; heat inactivation (56% for 30 minutes) and gander erythrocyte absorption, then tested against 10 arbovirus antigens. The antigens were produced from suckling mouse brain infected with Tembusu (TMU) strain no. MM 1775, Zika (ZKA) strain MR 766, dengue-1 (DEN-l) prototype strain, dengue-2 (DEN-2) NGC, JE, prototype strain, West Nile (WN) B 956, Kunjin (KUN) M RM 16, Ross River (RR) T-48, chikungunya (CHIK) S-27, Sindbis (SIN) EgAr 338 or Bunyamwera (BUN) original strain viruses. Antigens were made using the sucrose acetone

Table I-Results of HI tests on 235 human from the Hong Kong area

Virus antigen

sera

Number positive Number tested

TMU ZKA DEN-l DEN-2 EN

241235 11/235 18/149 17/176 351235 141235 371235 O/235 31235 23/235 21235

KUN RR CHIK SIN BUN

Percentage positive 10.2 4.6

extraction method of CLARKE & CANALS (1958) with additional protamine sulphate treatment (WARREN et al., 1949) or sonication (ARDOIN et al., 1969) when required. Some antigens were produced using the arcton extraction method of PORTERFIELD & ROWE (1960). The haemagglutination-inhibition (HI) test of CLARKE & CASALS (1958) adapted to the micromethod of SEVER (1962) was used. Results

and Dfscussion

HI tests were carried out on 235 human sera against some or all of the listed antigens. None of the patients were suspected of having had or to be convalescing from an arbovirus infection. The HI responses to KUN antigen were most common with 37 (15.7 %) of the sera positive (Table I). Only four of these reactions were monospecific, although nine of the KUN positive sera exhibited higher titres against KUN than other flaviviruses. Reactions to JE were the second most common with 35 sera (14 *9 %) having antibodies, 16 being monospecific. TMU positive reactions occurred in 24 (10.2 %) of the sample. Only two of these were monospecific and one serum exhibited a four-fold higher TMU titre over KUN (1:80 vs 1:20) and was negative against JE. Antibodies against DEN-l (18/149; 12.0%) and DEN-2 (17/176; 9.6%) always crossed

B. K. JOHNSON

595

et d.

Table II-III results on serum samples when age and sex of patients were known (no results for DEN-O). The numbers within brackets indicate the percentage positive Females Age group Antigen TMU ZKA DEN-l 4FN KUN RR CHIK SIN BUN