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Haeorrhagic fever in Democratic Republic of Congo identified as Marburg
NEWS Public-health message about dioxin remains unclear
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xposure to the industrial contaminant 2,3,7,8-tetrachlorodibenzop-dioxin (TCDD) increases the occurrence of all types of cancers, but only when exposures are 1000 times greater than those recorded for the general US population, say scientists. These new results are “not something most people in the USA should be concerned about, though exposures may be greater elsewhere in the world”, comments lead author Kyle Steenland (US National Institute for Occupational Safety and Health, Cincinnati, OH, USA). Regulatory agencies have long been divided about whether TCDD —produced mainly as a result of waste incineration—is carcinogenic, and if so, what the safe exposure limit is and how to measure exposures. To help resolve these issues, Steenland and co-workers studied causes of death for 5132 workers at 12 US chemical plants and estimated TCDD exposures for a subset of the cohort. The standardised mortality ratio (SMR) for the cohort as a whole was 1·13, a significant but modest excess. However, in the subset analysis,
with increasing cumulative exposure to TCDD there was a significant trend of increasing SMRs for all cancers, with a 60% increase in SMR in people with the highest exposure. Comparisons between workers with the highest and the lowest exposures also showed associations between exposure to TCDD and smoking-related cancers, other cancers, and ischaemic heart disease (J Natl Cancer Inst 1999; 91: 779–86). Michael Kamrin, a toxicologist at Michigan State University (East Lansing, MI, USA), calls the data “unconvincing and epidemiologically weak”. Many of the associations are not significant, he says, and the confidence intervals are such that “you don’t really know whether there is a positive or negative effect. And if you’re dealing with all kinds of cancers, you have an indefinite number of confounders. These data don’t
suggest to me that there’s any health risk from dioxin [TCDD]. I didn’t think so before, and I don’t now”. Because the major source of dioxin is incineration, whenever a new incinerator site is proposed, local residents become very agitated, says Robert Hoover of the US National Cancer Institute (Bethesda, MD, USA), “but the risks of TCDD are not huge even in the very highly exposed, and while they are important, the implication is that the risks for any level of exposure are going to be quite small”. Does this that mean people can safely live near incinerators? “Whether the risk is acceptable or not is a dilemma for individuals and regulatory agencies”, admits Hoover. “And with levels of risk as low as these, the epidemiological data are unlikely to help solve the dilemma.” Marilynn Larkin
Haemorrhagic fever in Democratic Republic of Congo identified as Marburg
M
arburg virus has been con firmed as the cause of death of one person affected by an epi demic of haemorrhagic fever in the Democratic Republic of Congo. 90 cases of haemorrhagic fever have been reported, mostly since late March and mostly in the northern town of Durba. 60 people have died. “There is now strong evidence that Marburg is at the origin of the epidemic”, says Marc Biot of Médecins Sans Frontières (MSF), who led the investigation. Marburg haemorrhagic fever —a rare human and primate disease — is caused by a filovirus, as is Ebola. Symptoms of fever and haemor rhage, and a high fatality rate led many to suspect that the current epidemic was caused by Ebola. There is no specific treatment or
THELANCET • Vol 353 • May 15, 1999
vaccine for Ebola or Marburg. Only six cases of human Marburg have been previously identified in the wild, but now a link has been suggested between Marburg virus and “Durba syndrome”, a fever that has killed more than 60 people since its discovery in 1993. Sera tested last week from a patient who had Durba syndrome in 1994 con tained antibodies to Marburg virus. However, samples from six other cases of the current epidemic were negative for all suspected pathogens, including Marburg. Further epidemiological studies —involving teams from MSF, the US Centers for Disease Control and Prevention, WHO, the Tropical Institute of Antwerp, Belgium, and the South African National Institute of Virology —are underway.
Most of the cases have been among men working illegally in abandoned mines near Durba. “The mines are very unhygienic”, says Biot. “The miners are living and working where there is a lot of excreta from rats and bats.” He adds that little is known about how Marburg virus spreads, and that the mines could provide the first opportunity to study transmission routes, reservoirs, and vectors. MSF, who has set up an isolation unit for patient care in Durba, is advising health authorities and the general public in the area and is distributing barrier nursing mate rials for health workers. Nearby countries are closely monitoring the epidemic. Nathan Ford
1681
E
xposure to the industrial contaminant 2,3,7,8-tetrachlorodibenzop-dioxin (TCDD) increases the occurrence of all types of cancers, but only when exposures are 1000 times greater than those recorded for the general US population, say scientists. These new results are “not something most people in the USA should be concerned about, though exposures may be greater elsewhere in the world”, comments lead author Kyle Steenland (US National Institute for Occupational Safety and Health, Cincinnati, OH, USA). Regulatory agencies have long been divided about whether TCDD —produced mainly as a result of waste incineration—is carcinogenic, and if so, what the safe exposure limit is and how to measure exposures. To help resolve these issues, Steenland and co-workers studied causes of death for 5132 workers at 12 US chemical plants and estimated TCDD exposures for a subset of the cohort. The standardised mortality ratio (SMR) for the cohort as a whole was 1·13, a significant but modest excess. However, in the subset analysis,
with increasing cumulative exposure to TCDD there was a significant trend of increasing SMRs for all cancers, with a 60% increase in SMR in people with the highest exposure. Comparisons between workers with the highest and the lowest exposures also showed associations between exposure to TCDD and smoking-related cancers, other cancers, and ischaemic heart disease (J Natl Cancer Inst 1999; 91: 779–86). Michael Kamrin, a toxicologist at Michigan State University (East Lansing, MI, USA), calls the data “unconvincing and epidemiologically weak”. Many of the associations are not significant, he says, and the confidence intervals are such that “you don’t really know whether there is a positive or negative effect. And if you’re dealing with all kinds of cancers, you have an indefinite number of confounders. These data don’t
suggest to me that there’s any health risk from dioxin [TCDD]. I didn’t think so before, and I don’t now”. Because the major source of dioxin is incineration, whenever a new incinerator site is proposed, local residents become very agitated, says Robert Hoover of the US National Cancer Institute (Bethesda, MD, USA), “but the risks of TCDD are not huge even in the very highly exposed, and while they are important, the implication is that the risks for any level of exposure are going to be quite small”. Does this that mean people can safely live near incinerators? “Whether the risk is acceptable or not is a dilemma for individuals and regulatory agencies”, admits Hoover. “And with levels of risk as low as these, the epidemiological data are unlikely to help solve the dilemma.” Marilynn Larkin
Haemorrhagic fever in Democratic Republic of Congo identified as Marburg
M
arburg virus has been con firmed as the cause of death of one person affected by an epi demic of haemorrhagic fever in the Democratic Republic of Congo. 90 cases of haemorrhagic fever have been reported, mostly since late March and mostly in the northern town of Durba. 60 people have died. “There is now strong evidence that Marburg is at the origin of the epidemic”, says Marc Biot of Médecins Sans Frontières (MSF), who led the investigation. Marburg haemorrhagic fever —a rare human and primate disease — is caused by a filovirus, as is Ebola. Symptoms of fever and haemor rhage, and a high fatality rate led many to suspect that the current epidemic was caused by Ebola. There is no specific treatment or
THELANCET • Vol 353 • May 15, 1999
vaccine for Ebola or Marburg. Only six cases of human Marburg have been previously identified in the wild, but now a link has been suggested between Marburg virus and “Durba syndrome”, a fever that has killed more than 60 people since its discovery in 1993. Sera tested last week from a patient who had Durba syndrome in 1994 con tained antibodies to Marburg virus. However, samples from six other cases of the current epidemic were negative for all suspected pathogens, including Marburg. Further epidemiological studies —involving teams from MSF, the US Centers for Disease Control and Prevention, WHO, the Tropical Institute of Antwerp, Belgium, and the South African National Institute of Virology —are underway.
Most of the cases have been among men working illegally in abandoned mines near Durba. “The mines are very unhygienic”, says Biot. “The miners are living and working where there is a lot of excreta from rats and bats.” He adds that little is known about how Marburg virus spreads, and that the mines could provide the first opportunity to study transmission routes, reservoirs, and vectors. MSF, who has set up an isolation unit for patient care in Durba, is advising health authorities and the general public in the area and is distributing barrier nursing mate rials for health workers. Nearby countries are closely monitoring the epidemic. Nathan Ford
1681