Apart from HIV two exogenous retroviruses (human T cell leukaemia viruses type I (HTLV-I) and type II (HTLV-II)) infect humans. HTLV-I infection is endemic in Japan, the Caribbean, Africa, and Melanesia and is found among immigrants from these regions in Europe. HTLV-I infection is associated with a 1-5% lifetime risk of adult T cell leukaemia/lymphoma,1 a 0.25% lifetime risk of HTLV-I associated myelopathy,2 and other inflammatory conditions (uveitis, alveolitis, and arthritis).1 HTLV-II infection is endemic in some native American and African peoples and among injecting drug users and has been associated with neurological disease.1 Between 1986 and 1992,100 cases of HTLV-I associated myelopathy and 44 cases of adult T cell leukaemia/lymphoma were diagnosed in the United Kingdom.3 Adult T cell leukaemia/lymphoma was first described in 1977 and patients with it have a mean life expectancy of only six months, so most of the 44 cases were probably incident cases. However, HTLV-I associated myelopathy causes prolonged morbidity and was not recognised as a clinical entity until 1985; thus the 1986-92 data may include many prevalent cases. We therefore sought to determine the incidence of HTLV-I/II related diseases in England and Wales since 1992.
Methods and results
A serological diagnosis of HTLV-I infection is essential for the diagnosis of related disease, and case ascertainment was therefore based on a review of requests made to two national reference laboratories. Samples repeatedly reactive in screening assays were further examined for HTLV-I and II type specific antibodies by Western blot (GeneLabs HTLV 2.3/2.4, Singapore) or Select-HTLV (Biochem ImmunoSystems, Montreal). Clinical data on HTLV-I/II infected subjects first tested in 1993-7 inclusive were collected from referral forms, with additional medical details being requested from the referring centres as appropriate.
Subjects who were seropositive for HTLV-I were classified as having adult T cell leukaemia/lymphoma if this or lymphoma with hypercalcaemia was documented. All other cases of lymphoma were classified as “other lymphoma.” Similarly, subjects who were seropositive for HTLV-I were classified as having HTLV-I associated myelopathy if this or myelopathy or “?MS[multiple sclerosis]” or signs and symptoms consistent with myelopathy were documented. All other cases were classified as “other neurology.” Of 3900 subjects tested, 264 were seropositive for HTLV-I or HTLV-II, of whom 220 were symptomatic (table). Of the 110 HTLV-I seropositive subjects, 94 (85%) were of Afro-Caribbean origin; 174 (66%) of the subjects seropositive for HTLV-I or HTLV-IIpresented in London. The female:male ratio was 2:1 for adult T cell leukaemia/lymphoma (mean age 52 (range 26-71)) and 3:1 for HTLV-I associated myelopathy (mean age 56 (28-83)).
About one million people living in England and Wales originate from areas where HTLV-I is endemic (1991 census).4 Using seroprevalence rates applicable to region of birth for those who were born outside the United Kingdom and the seroprevalence among women of different ethnic groups attending antenatal clinics in London, we estimate that 22 500 people of Caribbean or African origin living in England and Wales are infected with HTLV-I.
Comment
Assuming 22 500 HTLV-I infected people and a lifetime risk of 1-5%,1 the number of cases of adult T cell leukaemia/lymphoma observed each year (10) falls within the expected range (4-22). Conversely, if the lifetime risk of developing HTLV-I associated myelopathy is 0.25%2 only one new case a year would be expected in England and Wales, whereas there was an annual incidence of 12 new diagnoses, with no significant trend since 1992. This suggests either that the lifetime risk of myelopathy among HTLV-I infected people in the United Kingdom is about 3% and not 0.25% or that HTLV-I infection is more widespread in the population than we estimate.
These data have important implications for cost efficacy studies of interventions to prevent HTLV-I transmission in Europe (for example, antenatal or blood donor screening) as until now analysts have mainly relied on Japanese data.5 Furthermore, the possibility of other HTLV-I associated conditions (uveitis, arthritis, alveolitis) seems to be rarely considered by clinicians.
Table.
Known HTLV-I infections by year and diagnosis in England and Wales, 1993-7
| No of cases
|
Annual incidence (95% CI) | ||||||
|---|---|---|---|---|---|---|---|
| 1993 | 1994 | 1995 | 1996 | 1997 | Total | ||
| HTLV-I associated myelopathy | 18 | 10 | 9 | 16 | 10 | 63 | 12.6 (9.7 to 16.1) |
| Other neurology | 2 | 3 | 3 | 4 | 5 | 17 | 3.40 (1.98 to 5.44) |
| Adult T cell leukaemia/lymphoma | 20 | 9 | 6 | 10 | 6 | 51 | 10.2 (7.6 to 13.4) |
| Other lymphoma | 2 | 3 | 5 | 3 | 7 | 20 | 4.0 (2.44 to 6.18) |
| Polymyositis | 1 | 1 | 0 | 1 | 2 | 5 | 1.00 (0.32 to 2.34) |
| Strongyloides stercoralis infection* | 3 | 2 | 1 | 3 | 0 | 9 | 1.80 (0.82 to 3.42) |
| Other medical conditions† | 5 | 2 | 5 | 2 | 4 | 18 | 3.60 (2.14 to 5.70) |
| HIV-1 infection | 1 | 2 | 0 | 0 | 1 | 4 | 0.80 (0.22 to 2.04) |
| HTLV-II infection‡ | 3 | 0 | 1 | 1 | 0 | 5 | 1.00 (0.32 to 2.34) |
| No information | 3 | 8 | 7 | 4 | 6 | 28 | 5.60 (3.72 to 8.10) |
| Total of clinical requests | 58 | 40 | 37 | 44 | 41 | 220 | 44.0 (38.4 to 50.2) |
| Contact§ | 6 | 7 | 9 | 6 | 2 | 30 | NA |
| Donor¶ | 2 | 3 | 2 | 7 | 0 | 14 | NA |
| Total of all requests | 66 | 50 | 48 | 57 | 43 | 264 | NA |
NA=Not applicable.
Includes one case of strongyloidiasis in a patient with lymphoma
Excludes other recognised HTLV-I associated diseases.
Includes one case of HTLV-II associated myelopathy.
Asymptomatic individual tested for HTLV-I/II because a family member or sexual partner ws known to have HTLV-I/II infection.
Blood donor screened for HTLV-I/II.
Acknowledgments
We thank colleagues in the Hepatitis and Retrovirus Laboratory, Central Public Health Laboratory; Peter Luton and colleagues in the Diagnostic Section, Department of Virology, University College Hospital, London; and colleagues in the regional laboratories of the Public Health Laboratory Services for their help in this study. The data were collated as part of an initiative on HTLV infection and disease in Europe supported by the European Community Biomed Programme (CT 98-3781).
Footnotes
Funding: None.
Competing interests: None declared.
References
- 1.International Agency for Research on Cancer. Human immunodeficiency viruses and human T-cell lymphotrophic viruses. Lyons: IARC; 1996. . (IARC Monographs on the Evaluation of Carcinogenic Risk to Humans, Vol 67.) [Google Scholar]
- 2.Kaplan JE, Osame M, Kubota H, Igata I, Nishitani H, Maeda Y, et al. The risk of development of HTLV-I associated myelopathy/tropical spastic paraparesis among persons infected with HTLV-I. J Acquir Immun Defic Syndr. 1990;3:1096–1101. [PubMed] [Google Scholar]
- 3.Simms I, Tosswill JHC, Noone A, Morgan D. Surveillance of HTLV infection in England and Wales: 1986-1992. Commun Dis Rep CDR Rev. 1994;4:R65–R69. [PubMed] [Google Scholar]
- 4.Haskey J. Population review. 8: The ethnic minority and overseas-born populations of Great Britain. Popul Trends. 1997;88:13–30. [PubMed] [Google Scholar]
- 5.Tynell E, Andersson S, Lithander E, Arneborn M, Blomberg J, Hansson HB, et al. Screening for human T-cell leukaemia/lymphoma virus among blood donors in Sweden; cost effectiveness analysis. BMJ. 1998;316:1417–1422. doi: 10.1136/bmj.316.7142.1417. [DOI] [PMC free article] [PubMed] [Google Scholar]