Influenza in East Africa

Bull Org. moltd. Satg ) 1970, 43, 269-273 Bull. Wld Hlth Org. Influenza in East Africa, 1969-70 D. MONTEFIORE,1 S. G. DROZDOV,2 G. W. KAFUKO,' 0. A. FAYINKA41 & A. SONEJI' Very little information is available concerning the frequecwy ofinlenza in East Africa. Following recent outbreaks of influenza in Uganda, that were due to the A2/Hong Kongl 68 virus, it was considered useful to obtain information relating to the prevalence of in- fection due to this virus and to the current strain of influenza B wrw, not only in Uganda but also in the neighbouring territories of Kenya and Tanzania. 77 results of serological testing of sera showed that widespread outbreaks of influenza A2/Hoxg Kong/68 infection had occurred recently in all three territories, while there was evidence ofsporadic infection in all territories by the current influenza B strain. Despite the faowable climate of East Africa, it is evident that widespread outbreaks of influenza ca occur, and these may arise during the period of the year when influenza is rare in coutries with temperate cli- mates. Influenza can easily spread to other countries via ar traveltm to and from East Africa. Very little information has been published con- cerning the frequency of influenza in East Africa. In a recent paper (Montefiore et al., 1970), we reported the occurrence of outbreaks of infection in Uganda due to the A2/Hong Kong/68 strain of influenza virus, and showed that it had probably entered the country about June 1969 and had then gradually spread to all areas. This strain of virus is known to have been present in Kenya in April 1969 (Wkly epidem. Rec., 1969), but so far there have been no reports of its occurrence in Tanzania. Information on the occurrence of influenza B infection is even scantier, the sole references to it that we could find being a report, without further details, of the isolation during 1966 of a strain of influenza B in Johannesburg, South Africa (Wkly epidem. Rec., 1966) and a mention of a wave of influenza B infection in South Africa during March 1969 (Gear, 1969). The present report deals with serological findings relating to the A2/Hong Kong/68 and to B/Massa- chusetts/3/66 strains of influenza virus: sera from Uganda, Kenya and Tanzania were tested for anti- bodies to these two current strains, and the presence IHead, WHO Virus Study Team, East African Virus Research Institute, Entebbe, Uganda. 'WHO Virus Study Team, East African Virus Research Institute. 'Director, East African Virus Research Institute. 'Technical Officer, WHO Virus Study Team, East African Virus Research Institute. of infection by both types of vim has been demon- strated. MATERIALS AM)WIHODS Serological methods Sera were transported to the laboratory, either by air or by road, according to distance, in refrige- rated containers at +4C, separated and stored at -20°C until tested. Theywere tested for haemaggluti- nation-inhibiting (HI) antbodies to influenza A2/ Hong Kong/68 and inflza B/Mass/3/66, these being the current strains of virus as supplied by the World Health Organization to influenza reference laboratories. Standard methods were used, and all sera were treated with receptor-destroying enzyme before testing. In all tests 8 haesagglutination units of antigen were used; the antigen was prepared from the allantoic fluid of embonated eggs infected with the seed virus suppLied by the World Health Organization. Serum samples Serum samples were obtained from random selec- tions of patients attending hospitals in Kabale (south-west Uganda), Moroto (north-east Uganda), Mombasa (Kenya) and Arusna (Tanzania). Serum samples were also obtained from prisoners in Soroti Prison (Central Uganda), who were suffering from an outbrek of infection due to influenza A2/Hong Kong/68 vwirus. Details of this 2552 269 D. MONTEFIORE AND OTHERS HAEMAGGLUTINATION-INHIBITING ANTIBODY TITRES AMONG SERA FROM EAST AFRICA Influenza A2/Hong KongI68 Influenza B/Mass/3/66 Age-group Geometric mean No. of No. of sera Geometric mean(years) ~~No. of No. of seraf totreftitre(years) grseratpositivesera { positi (positives only) sera positive (positives only) Sera from Kabale (Uganda) 0-10a 2 1 (50%) 40.0 2 1 (50%) 20.0 11-20 31 7 (22.6%) 40.0 30 b 4 (13.3%) 20.0 21-40 27 5 (18.5%) 46.0 27 4 (14.8%) 25.2 >40 13 3 (23.1%) 31.8 13 1 (7.7%) 20.0 Total 73 16 (21.9%) 41.2 72 10 (13.9%) 21.4 Sera from Moroto (Uganda) 0-10 a 1 0 1 0 11-20 11 0 - 11 0 21-40 25 4 (16%) 47.6 25 0 _ >40 12 0 - 11 b 1(9.1%) 20.0 Total 49 4 (8.2%) 47.6 48 1 (2.1%) 20.0 Sera from Kenya 0-10C 25 6 (24.0%) 44.9 25 1 (4.0%) 1 :20d 11-20 19 10 (52.6%) 32.5 19 2 (10.5%) 1 :20 d I :40 ' 21-40 9 3 (33.3%) 63.5 9 1 (11.1%) 1 :20 d >40 4 2 (50%) 40.0 4 0 Total 57 21 (36.8%) 40.0 57 4 (7.0%) 23.8 Sera from Tanzania 0-10 c 33 21 (63.6%) 42.7 33 7 (21.2%) 26.9 11-20 38 29 (76.3%) 72.7 38 18 (47.8%) 25.2 21-40 14 10 (71.4%) 69.6 14 2 (14.3%) 28.2 >40 5 5 (100%) 69.6 5 2 (40.0%) 28.2 Total 90 65 (72.2%) 60.6 90 29 (32.2%) 25.8 a No children in 0-5-year age-group. b' I serum insufflcient for test for influenza B/Mass/3/66. C0-5-year age-group: Influenza A2/Hong Kong/68, 2 of 11 sera positive (18.2%); influenza B/Mass/3/66, 1 of 11 sera positive (9.1%). d Individual titres. e 0-5-year age-group: influenza A2/Hong Kong/68, 11 of 19 sera positive (57.9%); influenza B/Mass/3/66, I serum of 19 posi- tive (5.3%), this patient being 5 years old. 270 INFLUENZA IN EAST AFRICA, 1969-70 outbreak have been published elsewhere (Monte- fiore et al., 1970), and in this report only the findings in respect of influenza B/Mass/3/66 are recorded. Similarly, a small number of sera were obtained from university students in Kampala, south Uganda, during an outbreak of infection due to the A2/Hong Kong/68 virus, though only the findings with regard to influenza B are recorded in this report. RESULTS Uganda Kabale (south-west Uganda). A total of 73 sera were collected during January 1970 from a random selection of patients attending hospital in Kabale. The findings are shown in the table. A higher proportion of the population studied had anti- bodies to the A2/Hong Kong/68 than to the B strain of influenza virus, and the titres of antibodies to the former virus were higher than to the latter. There had been outbreaks of influenza-like illnesses in two schools in the town about a month before the sera were collected, and it seems likely that the higher titres and frequency of antibodies to influenza A2/Hong Kong/68 virus indicate that this was also circulating among the population as a whole at this time. Moroto (north-east Uganda). A total of 49 sera were collected during January 1970 from a random selection of patients attending the hospital in Moroto. The findings are shown in the table. Moroto is situated in a very isolated part of Uganda, with only limited contact with the rest of the country. The low percentage infected by influenza A2 Hong Kong/68 virus probably reflects this isolation. Only one serum showed antibodies to influenza B/Mass/ 3/66 virus, and that was from a subject over 40 years of age. It would appear that this virus has not been circulating at all widely in the area recently. Soroti (central Uganda). A total of 98 sera were collected from prisoners in Soroti prison during October 1969 at the time of an outbreak of infection due to the A2/Hong Kong/68 virus. The prisoners were all males, aged between 19 and 40 years. The findings with regard to antibodies to A2/Hong Kong/68 virus have been re- ported elsewhere (Montefiore et al., 1970), but it may be said here that 28.5% of the samples taken at the start of the outbreak contained antibodies, at a titre of 1: 20 or over, to B/Mass/3/66. The geometric mean titre of these positive sera was 29.0. The findings suggest that at some time pre- viously B/Mass/3/66 virus had been circulating fairly freely among this closed community. Kampala (south Uganda). A total of 11 sera were obtained from university students during January 1970, again during an outbreak of infection due to the A2/Hong Kong/68 virus. Four of these sera contained antibodies to the B strain of virus and showed a geometric mean titre of 23.8. The findings again suggest that influenza B had been circulating fairly freely among this closed community at some time previously. Kenya A total of 57 sera were obtained during February 1970 from a random selection of patients attending hospital in Mombasa, Kenya. The findings are shown in the table. The results indicate that there had been a fairly widespread outbreak of infection due to A2/Hong Kong/68 virus recently, as judged by the relatively high HI antibody titres. It appears that there had also been sporadic outbreaks of infection due to the influenza B strain of virus previously. Tanzania A total of 90 sera were obtained during February 1970 from a random selection of patients attending hospital in Arusha, Tanzania. The findings are shown in the table. This town is the administrative centre for the East African Community, and conse- quently receives many visitors from widely scattered areas. The results show a strikingly high frequency of antibodies to A2/Hong Kong/68 virus, geometric mean titres being high in each age-group. These results clearly indicate a recent and widespread outbreak of infection due to this virus. The fre- quency of antibodies to the influenza B strain is also relatively high, although the titres of antibodies are lower. This virus must also have previously been circulating freely, although it is of considerable interest to note that of 19 sera taken from children aged 5 years or less, only 1 serum was positive for antibodies to the B strain, while 11 sera (57.9%) were positive to the A2 strain of influenza virus. DISCUSSION In temperate climates influenza is generally asso- ciated with the winter months, the incidence of clinical infection falling to very low levels during the warm summer period. It is of interest, therefore, to note that the disease can also be widespread in 271 D. MONTEFIORE AND OTHERS East Africa, where the weather is regularly warm and sunny. With regard to the current epidemic strain, A2/Hong Kong/68, by far the highest frequency was found in Arusha, the administrative centre of the East African Community, which is heavily populated and has extensive contact through visitors with the rest of East Africa. As might be expected, the lowest frequency was found in Moroto, a small town in an isolated area of Uganda, al- though even here there was evidence of recent infection with the virus. A relatively high frequency of infection was also detected among sera collected from Mombasa, the main port of entry to Kenya, while infection was also common in Kabale, a town in a heavily populated area of Uganda. In East Africa, therefore, it seems that the frequency of infection with this virus is directly correlated with population density and movement. A somewhat similar picture emerges with regard to infection by the B/Mass/3/66 virus, although in this case there is a disproportionately low fre- quency of infection among the Mombasa population samples. In Uganda, as might be expected, the highest frequency of antibodies to this virus were found among sera taken from persons living in closed communities-the prison in Soroti and the university in Kampala. From the results reported it is clear that despite the favourable climate of East Africa, influenza infection can spread widely throughout the popu- lation, and can give rise to very extensive outbreaks of the disease, as in Arusha, Tanzania. In our earlier report (Montefiore et al., 1970) it was pointed out that the infection can occur in East Africa during the period of the year corresponding to the summer months in the northern hemisphere. It is clear that with extensive air and sea travel to East Africa, this area can form a reservoir for the infection which can then be easily conveyed to other parts of the world, where it can then spread when the condi- tions are suitable. ACKNOWLEDGEMENTS We would like to thank the Permanent Secretaries of the Ministries of Health of Uganda and Kenya, and the Principal Secretary, Ministry of Health andSocial Services, Tanzania, for their help in arranging the collec- tion of specimens. We would also like to thank Dr E. N. Mugola, Medical Superintendent of Cape Province General Hospital, Mombasa, Kenya, and the Regional Medical Officers, Arusha Region, Tanzania, for the collection and des- patch of serum samples. We also thank the medical and nursing staff of the hospital and clinics in Uganda, who kindly assisted us in the collection of samples from patients in Uganda. RESUMIt LA GRIPPE EN AFRIQUE ORIENTALE (1969-70) On ne dispose que de tres peu de donnees sur la fr6- quence de la grippe en Afrique orientale. Une enquete sero6pidemiologique apporte la preuve de l'infection grippale due aux virus A2/Hong Kong/68 et B/Massa- chusetts/3/66 en Ouganda, au Kenya et en Tanzanie. Des serums ont ete preleves chez des malades frequen- tant des consultations d'hopitaux et examines par l'epreuve d'inhibition de l'hemagglutination. A Kabale, dans une region tres peuplee de l'Ouganda, 21,9% des serums renfermaient des anticorps anti-A2/Hong Kong/68 et 13,9% des anticorps antigrippaux pour la souche B. Les titres plaidaient en faveur d'une infection grippale A d'origine recente. A Moroto, dans un territoire recule de l'Ouganda, la prevalence des anticorps antigrippaux n'atteignait que 8,2% (souche A2/Hong Kong/68) et 2,1 % (souche B/Massachusetts/3/66). A Soroti (Ouganda central), 28,5% des s6rums preleves chez des d6tenus renfermaient des anticorps antigrip- paux B a des titres de 1: 20 ou plus, tandis qu'a Kampala (Ouganda meridional), 4 serums d'etudiants sur 11 etaient positifs pour cette meme souche. A Mombasa (Kenya), des serums recueillis apres un echantillonnage aleatoire ont fourni un taux de positivit6 de 36,8% pour le virus A2/Hong Kong/68, avec des titres IH relativement 6lev6s signant une infection recente. Des anticorps antigrippaux B ont ete deceles dans 7,0% des serums. A Arusha (Tanzanie), l'examen de serums a r6vele une poussee recente et 6tendue d'infections grippales A (72,2% de s6rums positifs) et une certaine activite, dans le passe, de la grippe B (32,2% de serums positifs). Cette prevalence 6lev6e des anticorps antigrippaux est attribu6e 272 INFLUENZA IN EAST AFRICA, 1969-70 273 a la forte densit6 de la population de cette ville, siege administratif de la Communaute est-africaine, qui regoit en outre de tres nombreux visiteurs venus d'autres pays d'Afrique orientale. II semble qu'en Afrique orientale la frequence de l'infection grippale soit li6e trFs 6troitement a la densite et aux mouvements de la population. En depit de condi- tions climatiques favorables, cette partie de I'Afrique n'est pas a l'abri d'6pid6mies de grippe et repr6sente un r6servoir potentiel de l'infection. REFERENCES Gear, J. H. S. (1969) Bull. Wld Hlth Org., 41, 409 Montefiore, D., Drozdov, S. G., Kafuko, G. W., Fayinka, 0. A. & Soneji, A. (1970) Trop. geogr. Med. (in press) Wkly epidem. Rec., 1966, 41, 656 Wkly epidem. Rec., 1969, 44, 304 5