Surveillance of orthopoxvirus infections, and associated research, in the period after smallpox eradication

Bulletin of the World Health Organization, 60 (3): 367 - 375 (1982) Surveillance of orthopoxvirus infections, and associated research, in the period after smallpox eradication I. ARITA' & A. GROMYKO 2 In 1980, the World Health Assembly declared the global eradication ofsmallpox and recommended the universal discontinuation of smallpox vaccination; nevertheless, it recommended that surveillance and research on orthopoxvirus infections should continue. By early 1982, all except 8 countries in the world had stopped routine vaccination pro- grammes and all except I no longer required an international certificate ofsmallpox vacci- nation for travellers. Since 1978, as a result ofcontinuing active surveillance, 176 smallpox rumours have been investigated in 60 countries. Two ofthese concerned the two laboratory- associated cases that occurred in the United Kingdom in 1978; all the others were false alarms. Special surveillance programmes for human monkeypox have been developed in West and CentralAfrica. The number oflaboratories retaining variola virusstocks has been reduced tofour. Investigations to determine the identity and origin ofthe six known isolates of "whitepox" virus have continued. Research on mapping of variola DNA and on mono- clonal antibodies against certain orthopoxvirus antigens is continuing. All these measures are aimed at ensuring that the achievement ofsmallpox eradication is permanent. On 8 May 1980, the World Health Organization declared that the global eradication of smallpox had been achieved, but a resolution of the World Health Assembly recommended that although smallpox vaccination was no longer required, except for investi- gators at special risk, surveillance and research on orthopoxvirus infections should be continued at least for several years (1). This paper describes some aspects of the Organization's post-eradication pro- gramme of surveillance and research on orthopox- virus infections, and two other papers in this issue of the Bulletin present evidence concerning the identity (2) and origin (3) of the so-called "whitepox" virus isolates. CESSATION OF SMALLPOX VACCINATION An important benefit associated with the global eradication of smallpox was the recommendation of the World Health Assembly that smallpox vacci- nation should be discontinued in all countries. By 1 March 1982, 150 of the 158 WHO Member Statesa ' Chief, Smallpox Eradication, World Health Organization, 1211 Geneva 27, Switzerland. 2 Medical Officer, Smallpox Eradication, World Health Organiz- ation, Geneva. a Including 1 Associate Member. had officially terminated their smallpox vaccination programmes (Fig. 1). WHO has now been officially informed by all countries, except one, that the requirements for an international certificate of small- pox vaccination have been abolished. In Chad WHO has been unable to ascertain the present situation. Vaccination is niow recommended only for a very small number of investigators at special risk -those who still conduct variola virus research in a high security laboratory, handle vaccinia virus for vaccine production, conduct research on orthopoxviruses pathogenic to man, or who directly investigate human monkeypox cases. Despite these considerations, some reports of com- plications caused by smallpox vaccination have been published recently. During the last 24 months, for example, surveillance reports from Canada and the United Kingdom have included 6 and 9 cases, respectively, of vaccine complications. At least 8 cases, however, were in persons who, while not vacci- nated themselves, had been infected with vaccinia virus after being in contact with persons recently vaccinated. In some countries vaccination of recruits to the armed services has continued; these recruits will occasionally transmit vaccinia infection to unvacci- nated persons, and inevitably some of the compli- cations will be fatal. In the United Kingdom and Finland, smallpox vaccination of army recruits was discontinued in 1981. 4185 -367- 368 I. ARITA & A. GROMYKO XC .12 0 40. 0 40 0 Co SURVEILLANCE OF ORTHOPOXVIRUS INFECTIONS Table 1. Rumours of smallpox reported to WHO, 1 January 1978-1 March 1982 Final diagnosis No. No. of Smallpox Other Under WHO of countries or healed Monkey- Chicken- skin Erroneous investi- Region rumours involved smallpox pox pox Measles diseases report gation Americas 18 13 - - 12 1 - 5 - Africa 49 18 - 2 13 4 1 1 19 - Eastern Mediterranean 20 10 1 a - 4 - 3 12 - Europe 13 8 2 b - 7 1 2 1 - South-East Asia 65 7 2a - 29 1 1 9 13 1 Western Pacific 11 4 - - 5 1 1 4 - Total 176 60 5 2 70 18 26 54 1 0 Disease occurred prior to 1 977. b Laboratory associated cases in the United Kingdom, 1978. SURVEILLANCE OF SUSPECTED CASES OF SMALLPOX The last case of naturally occurring smallpox was reported from Somalia in October 1977. Between January 1978 and 1 March 1982, 176 smallpox rumours were reported to WHO from 60 countries throughout the world (Table 1). Investigation of these rumours revealed that five persons had suffered from smallpox. Three of the cases had occurred before 1977, and two occurred in 1978 in Birmingham, England, following accidental exposure at a micro- biological laboratory. An extensive investigation in Birmingham at that time did not reveal any additional cases. The other rumours were found to be associated with cases of chickenpox, measles, or other skin diseases. Of the total number of smallpox rumours reported since 1978, 50 were reported in 1978, 63 in 1979, 31 in 1980, 30 in 1981, and 2 at the beginning of 1982. Two WHO collaborating centres for the laboratory diagnosis of smallpox, monkeypox, and other poxvirus infections will be maintained at the Centers for Disease Control, Atlanta, USA and the Research Institute for Viral Preparations, Moscow, USSR, for as long as smallpox surveillance is re- quired. Some national laboratories are also partici- pating in the diagnosis of cases. For example, in India more than 2000 specimens have been examined during the last three years; all were negative. Early in 1981, WHO distributed to all national health administrations a document entitled "Manage- ment ofsuspected cases ofsmallpox in thepost-eradi- cation period" and this contains a practical guide on how to act on a report of a suspected case of smallpox. One of the important recommendations is that vacci- nation should not be done unless a presumptive diag- nosis of smallpox is established based on examination by a physician with extensive experience in the clinical diagnosis of smallpox and on a laboratory report that poxvirus particles have been demonstrated by elec- tron microscopy. Meanwhile, these post-eradication surveillance activities have identified two cases of human monkey- pox, the clinical picture of which was not distinguish- able from that of smallpox. One of these was detected in December 1978 when a physician in Benin reported to WHO that a case of smallpox-like disease had occurred in that country. A joint team from WHO and the health services of the Government of the People's Republic of Benin investigated the report, and human monkeypox was diagnosed. An adult, male, traditional herbalist had travelled to western Nigeria, developed fever and rash there, and was hos- pitalized on his return to Benin. The diagnosis of monkeypox was confirmed by virus isolation at a WHO collaborating centre. A total of 36 close contacts were investigated, 4 of whom had never been vaccinated. No secondary cases occurred. SURVEILLANCE OF MONKEYPOX VIRUS INFECTIONS Human monkeypox is an important disease in any post-eradication surveillance programme since its clinical features resemble those of smallpox (Fig. 2 and 3) and since its causative agent, monkeypox virus, belongs to the orthopoxvirus group and shares some 369 I. ARITA & A. GROMYKO antigens and other biological features with variola and vaccinia viruses. It is a rare zoonosis that occurs in tropical rain forest areas of West and Central Africa. The species of the animal reservoir is (are) not known. In 1979, a WHO/Zaire joint team collected liver, spleen, and kidney specimens from 1372 wild animals representing at least 98 species (non-human primates, rodents, squirrels, pangolins, etc.) in Equateur Region, Zaire. Laboratory investigation failed to recover poxvirus from any of these speci- mens. However, antibody specific to monkeypox virus has been found in a few wild monkeys captured in West Africa (4). Since 1970, when the first case of human monkey- pox was discovered in Equateur Region, Zaire, 63 cases from six countries have been confirmed by laboratory studies: Cameroon, 2; Ivory Coast, 2; Liberia, 4; Nigeria, 3; Sierra Leone, 1; and Zaire, 51. The majority of these 63 patients were children and only 7 were over 15 years of age. Only 5 patients had been previously vaccinated: 8 died. Of 139 unvacci- nated persons who had been in close contact with a primary monkeypox case, 6 developed rash within 7-20 days after contact and monkeypox was con- firmed by laboratory diagnosis. Although it is prob- able that some of these six were exposed to the same source of infection as the primary cases, it would be prudent to regard them all as "presumed secondary cases". Even so, the secondary attack rate (57o) was much lower than that of smallpox (25 - 407o). In West and Central Africa, all countries except Chad have discontinued obligatory smallpox vacci- nation programmes. Consequently the proportion of non-immunes in the population is rising rapidly. Since unvaccinated persons are susceptible to monkeypox infection, this situation might result in the increased occurrence of cases of human monkeypox, the true prevalence of which deserves further study. In order to clarify this point, sero- logical surveys are being carried out in Ivory Coast and Sierra Leone in West Africa, and in Congo and Zaire in Central Africa. From May to August 1981, 10 000 serum specimens were collected from unvacci- nated children who might have been exposed to monkeypox. Currently, these specimens are being tested by sensitive tests for specific poxvirus anti- bodies. Those found positive are then examined for monkeypox-specific antibody by means of a radio- immune precipitation test, or by radioimmunoassay with absorption. Health services in these four coun- tries are collaborating in the surveys. In Zaire, hospital-based surveillance is also being promoted. Zaire/WHO surveillance teams estab- lished close contact with 144 hospitals in Equateur, Kasai Oriental, and Bandundu Regions where clusters of human monkeypox cases have occurred. Since the majority of cases have been discovered through hospitals, these hospitals will become important monitoring units for reporting monkeypox cases. SURVEILLANCE OF "WHITEPOX" VIRUS AND WHITE VARIANTS OF MONKEYPOX VIRUS During the implementation of the global smallpox eradication programme, special attention was paid to strengthening the assurance that there was no animal reservoir of smallpox. However, a variola-like virus was isolated on six occasions from materials that were thought not to have originated from human sources and this caused concern. Because of their appearance on chick embryo chorioallantoic membrane (CAM) these six isolates have been termed "whitepox" viruses; there have also been two reports that similar viruses could be isolated from stocks of monkeypox virus. Research on these viruses has continued and some new findings are reported in this issue of the Bulletin (2, 3). The present situation is summarized below. "Whitepox" virus Of the six "whitepox" virus isolates so far reported, two were reported to have been obtained from monkey kidney tissue culture in a laboratory in Utrecht, the Netherlands, in 1964, and the other four were reported to have been isolated by the WHO Collaborating Centre for Poxvirus Infections, Moscow, from kidney tissue specimens collected from monkeys or rodents during an investigation of human monkeypox in Zaire from 1970 to 1975. How- ever, epidemiological data indicate that they do not constitute evidence of an animal reservoir of smallpox (5). These six isolates are indistinguishable from certain variola virus strains by both biological tests and DNA restriction analysis (2). However, further extensive investigations of these isolates have recently revealed that the first two originated as a result of laboratory contamination by one of two variola virus isolates from Vellore, India, that were being handled at the same time in the same laboratory (3). The results of further studies on the other four isolates are awaited, but it should be noted that post-eradication epidemio- logical surveillance has not produced any evidence of continuing transmission of smallpox or smallpox-like diseases in Equateur Region, Zaire, where the above four "whitepox" virus isolates were reported to have originated, nor has "whitepox" or variola virus been isolated from any post-eradication case of smallpox- like disease. 370 SURVEILLANCE OF ORTHOPOXVIRUS INFECTIONS White mutants of monkeypox virus The WHO collaborating centre reported that some white variants cloned from their monkeypox virus stocks were indistinguishable on CAM from "white- pox" or variola virus and that the passage of these monkeypox virus stocks through hamsters produced white variants of the same nature. However, careful follow-up studies in other WHO collaborating centres have failed to verify this finding (personal com- munication, K. R. Dumbell and J. H. Nakano, 1981). SURVEILLANCE OF OTHER POXVIRUSES During the smallpox eradication programme, as well as during the post-eradication period, a number of other poxviruses have been studied by the WHO collaborating centres. These investigations are briefly described below. Camelpox virus In Somalia, in 1977 - 79, during the smallpox surveillance programme, a number of camels were discovered with rash (Fig. 4) and camelpox virus was isolated by the WHO collaborating centre in Atlanta, USA. There was no evidence of the infection in the nomadic people in close contact with these camels. Camelpox virus produces pocks on CAM that closely resemble those of variola, but work in several labora- tories has clearly distinguished camelpox virus from variola by other biological characters and by DNA analysis. Cowpox virus Reports of human cowpox infections have been rare in recent years, and it is now doubted whether the cow is the reservoir host of the virus; it is possible that both the cow and man are only sporadic indicator hosts who become infected from an unknown reser- voir, although of course man can be infected from cows, and vice versa. Support for this view has come from the occurrence of spontaneous cowpox virus infections in persons having had no contact with cows (7), and from the isolation of cowpox virus, or closely related viruses, from cases of spontaneous infections in various exotic animal species, particularly in large felines, in various zoos (Moscow and two in the United Kingdom) (8). Recently a young tiger was found to be infected with cowpox virus in Stockholm (personal communication, K. R. Dumbell and J. Ake Espmark, 1981). The natural reservoir of one virus closely related to cowpox has been identified. Following the detection of orthopoxvirus antibodies in a significant propor- tion of the great gerbils found in the Turkmen Repub- lic, USSR, a virus very like cowpox was isolated and studied at the collaborating centre in Moscow, and subsequently named Turkmenia virus. The discovery of this virus gives credence to suggestions that the natural reservoir of cowpox virus might be sought in small wild rodents in the United Kingdom and Western Europe. Gerbilpox (taterapox) This virus was isolated from a wild gerbil captured in West Africa. It resembles variola virus in several biological characters, but the two can be distinguished by further biological characterization and by DNA analysis. Serological surveys in Zaire in 1979 indicated that orthopoxvirus infections are prevalent in many animal species. Studies of gerbil- specific antibody are being carried out and may be found among the orthopoxvirus antibodies found in these sera. Lenny virus This orthopoxvirus was isolated by the WHO collaborating centre in London from a female suffer- ing from a smallpox-like disease, who had a severe rash, and who died in Nigeria in 1969. The virus most closely resembled vaccinia but had some properties more like those of variola. It was suggested that it might be a recombinant between these viruses. No other case has ever been discovered. Tanapox virus This virus can cause one or a few skin nodules in man (Fig. 5). In an investigation in Zaire in 1978 - 81 more than 163 cases of tanapox infection were dis- covered. The reservoir is not known. Electron-micro- scopic pictures of tanapox virus resemble those of the other orthopoxviruses -variola, monkeypox, and vaccinia. However, tanapox does not belong to the orthopoxvirus group and can be distinguished from them by cultural and antigenic properties. A similar virus has caused outbreaks in monkey colonies in a few primate centres in California, Oregon, and Texas, USA. CONTROL OF VARIOLA VIRUS IN LABORATORIES With the successful eradication of smallpox the situation as regards variola virus has become unique. There is no evidence that the virus is maintained in either human or animal populations, and the virus is now kept in only four laboratories in four countries: 371 1. ARITA & A. GROMYKO South Africa, USSR, United Kingdom, and USA. A WHO inspection team has visited all these labora- tories during the last 18 months and has confirmed that the variola virus is being kept safely. During the last three years, work with variola virus has been carried out only in WHO collaborating centres in the United Kingdom and USA. Further inspection visits are planned, and will involve not only the inspection of the conditions under which the virus is kept but also discussions on the destruction of the virus, or its transfer to one of the other WHO collaborating centres if retention is no longer justified. SPECIAL RESEARCH Two fields of research are important following the eradication of smallpox. The first concerns the preparation of appropriate DNA maps of all ortho- poxviruses, including variola and monkeypox viruses. Currently, no known orthopoxvirus has shown a DNA pattern with the potential for mutation to a variola-like virus in one or a few steps. However, if a new poxvirus were to be found, it would be impor- tant to investigate the DNA to determine its possible relationship to variola virus. The current studies at the WHO collaborating centres in Atlanta, USA, and Porton Down, England, are providing data that will be useful for this purpose. In addition, variola DNA is being cloned in fragments so that the recombinant plasmid will be available for detailed studies of variola DNA without the hazards associated with the handling of variola virus. The second important field of research is related to the diagnosis of poxvirus infection. As interest in smallpox is waning rapidly, the chances of recogniz- ing a suspected case of smallpox early are becoming less. This implies that in the future the possibility of obtaining specimens from an active case with a rash may be remote, and that convalescent serum will be the only available specimens from such patients. However, since variola virus shares many antigens with other orthopoxiviruses, including monkeypox and vaccinia, it is often not possible to determine the diagnosis just by identifying antibody specific to orthopoxviruses. In recent years, WHO collaborating centres have developed methods to detect antibody specific to individual orthopoxviruses by hetero- logous serum adsorption using enzyme-linked immunosorbent assay (ELISA), or by demonstration of residual homologous antibody by radioimmuno- assay, immunofluorescence, or neutralization tests. However, these methods are time consuming and necessitate high titres in the starting material. Other methods such as radioimmune precipitation and a monoclonal antibody test are therefore being devel- oped at the Duke University Medical Center, Durham, USA, as a collaborative undertaking with WHO. CONCLUSIONS The objective of the post-smallpox eradication sur- veillance and research programme is to reassure the world community that the status of smallpox eradi- cation is permanent and that if an unexpected situ- ation should occur in the future, WHO would be ready to deal with it. WHO now has stockpiled approximately 100 million doses of freeze-dried vaccine in Geneva and New Delhi. Using bifurcated needles, this quantity would be sufficient to vaccinate at least 200 million people in an emergency. The WHO collaborating centre in Utrecht, the Nether- lands, is constantly monitoring the potency of these stocks. The vaccine will probably never be used, but the existence of this reserve provides a guarantee to the world that protection would be available if required. All the post-eradication activities described here are being supervised by the special WHO Committee on Orthopoxvirus Infections. In 1985, this Com- mittee will review the overall situation, evaluate the results of research and the epidemiological situ- ation at that time, and plan any further activities that may be considered desirable. ACKNOWLEDGEMENTS We are grateful to Professor Keith Dumbell, St Mary's Hospital Medical School, London, England, and Dr Frank Fenner, the John Curtin School of Medical Research, Canberra, Australia, for their valuable advice in the preparation of this paper. 372 Fig. 2. Case of smallpox. Fig. 3. Case of monkeypox. KA ) Fig. 4. Camel with camelpox rash. Fig. 5. Case of tanapox. SURVEILLANCE OF ORTHOPOXVIRUS INFECTIONS 375 RtSUMt SURVEILLANCE DES INFECTIONS A ORTHOPOXVIRUS ET ACTIVITES DE RECHERCHE CONNEXES APRES L'ERADICATION DE LA VARIOLE En 1980, I'Assembl6e mondiale de la Sante a proclame 1'eradication mondiale de la variole et recommande la cessa- tion de la vaccination antivariolique dans le monde entier; elle a n6anmoins recommande, aussi, de poursuivre les acti- vit6s de surveillance et de recherche concernant les infec- tions a orthopoxvirus. Au d6but de 1982 tous les pays du monde, a 1'exception de huit, ont interrompu leurs pro- grammes de vaccination systematique et tous, sauf un seul, ont cess6 d'exiger des voyageurs le certificat international de vaccination antivariolique. Depuis 1978, grAce A la pour- suite d'une surveillance active, 176 rumeurs ayant trait A des cas de variole ont 6t6 enquet6es dans 60 pays. II s'agissait dans tous les cas de fausses alertes. Des programmes speciaux de surveillance du monkeypox humain ont ete mis en oeuvre en Afrique occidentale et en Afrique centrale. A pr6sent, quatre laboratoires seulement conservent encore des stocks de virus variolique. Les enqu&es visant a d6terminer l'identit6 et l'origine des six isolements connus de virus du <<whitepox>> ont continue. De meme, on poursuit recherches pour 6tablir la carte de 1'ADN variolique et les travaux sur les anticorps monoclonaux dirig6s contre les antigenes de certains orthopoxvirus. Toutes ces mesures visent a faire en sorte que l'eradication de la variole soit definitive. REFERENCES 1. Final report of the Global Commission for the Certifi- cation ofSmallpox Eradication. Geneva, World Health Organization, 1980 (History of International Public Health, No. 4). 2. BEDSON, H. S. Enzyme studies for the characterization of some orthopoxvirus isolates. Bulletin of the World Health Organization, 60: 377-380 (1982). 3. DUMBELL, K. R. & KAPSENBERG, J. G. Identification of two "whitepox" viruses as variola strains from southern India. Bulletin of the World Health Organiz- ation, 60: 381 - 387 (1982). 4. BREMAN, J. G. ET AL. Human poxvirus disease after smallpox eradication. American journal of tropical medicine and hygiene, 26: 273 - 281 (1977). 5. ARITA, I. Virological evidence for the success of the smallpox eradication programme. Nature (London), 279: 293 - 298 (1979). 6. BAXBY, D. Is cowpox misnamed? A review of 10 human cases. British medical journal, 1: 1379 - 1381 (1977). 7. MARENNIKOVA, S. S. Field and experimental studies of poxvirus infections in rodents. Bulletin of the World Health Organization, 57: 461 - 464 (1979).