31 spray teams
Occupational
Medicine
EPIDEMIC MALATHION POISONING IN PAKISTAN MALARIA WORKERS MCWILSON WARREN RONALD D. DOBBIN STEVEN MILLER WINNIE R. TEETERS
of Epidemiology and Tropical Diseases, Center for Disease Control, Atlanta, Georgia 30333; National Institute for Occupational Safety and Health, Center for Disease Control, Cincinnati, Ohio 45202; and Pharmacology Laboratory, Technical Service Division, U.S. Environmental Protection Agency, Beltsville, Maryland 20705, U.S.A.
were
employed
in
Punjat
plied as a water-dispersible powder containing approximately 50% malathion and 50% carrier and was mixed in the field. Three formulations of malathion were used in 1976: an American company (brand 1) supplied 5700 tonnes, an Italian chemical company (brand 2) supplied 1000 tonnes, and another Italian company (brand 3) supplied 350 tonnes. with
EDWARD L. BAKER, JR. MATTHEW ZACK JAMES W. MILES LEE ALDERMAN
(7700 workers)
and North-West Frontier Province, the main areas oj malathion usage. Each spray team consisted of 1 mixer, 5 spraymen, and 1 field supervisor. Malathion was sup-
water
Bureaux
Epidemic Pesticide intoxication began to occur in late June, after the start of spraying. Intoxication was more common on Friday and Saturday (at the end of the sixsoon
day working week) than on Sunday (when no spraying place). The symptoms and clinical histories of these patients were consistent with organophosphate-insecticide intoxication;6 some workers experienced burns and rashes after skin contact with the pesticide. Workers using the Italian formulations reportedly had the most severe illnesses. Insecticide poisoning probably led to at least 5 deaths (2 mixers and 3 spraymen). 3 workers in areas where the Italian-formulated pesticide was used died after exposure during only their normal work activities. 2 deaths were reported from areas where the American formulation was used: 1 sprayman died shortly after he consumed food which had been sprayed, but death of a second sprayman was poorly documented. took
In 1976, epidemic organophosphate insecticide poisoning due to malathion occurred among 7500 field workers in the Pakistan malaria control programme. In July, the peak month of the epidemic, it is estimated that there were about 2800 cases. In field studies low red-cell cholinesterase activities were associated with the signs and symptoms of organophosphate insecticide intoxication. Toxicity was seen with 3 different formulations of the insecticide and was greatest with the products containing increased amounts of isomalathion, a toxic malathion degradation product. Poor work practices, which had developed when D.D.T. was the primary insecticide for malaria control, resulted in excessive skin contact with and percutaneous absorption of the pesticide. Airborne malathion concentrations were very low. Implementation of good work practices and proscription of use of the 2 pesticide formulations most contaminated with isomalathion halted the epidemic in September. An extensive training programme and surveillance system for pesticide toxicity preceded 1977 spraying operations.
Summary
INTRODUCTION
regarded as one of the safest organoin general use, and has replaced insecticides phosphorus D.D.T. and benzene hexachloride (B.H.C.) in malaria-control programmes as resistance to these compounds has developed in the Anopheles mosquito.2 Extensive field testing of malathion in malaria programmes in Uganda,3 Nigeria,4 and Central Americas demonstrated relatively little evidence of human toxicity. In the Ugandan and Nigerian studies, symptoms of pesticide intoxication and reduced cholinesterase activities were not encountered. In the Central American study, severe pesticide intoxication developed in 3 spraymen who wore uniforms wet with kerosene solutions of malathion for several days. We describe an epidemic of insecticide intoxication among field workers in the Pakistan malaria control proMALATHION is
METHODS AND RESULTS
Retrospective Questionnaire Survey The staff of the provincial malaria programmes interviewed a random sample (approximately 10%) of the spraymen, mixers, and supervisors in Punjab and NorthWest Frontier Province to estimate the prevalence of pesticide-intoxication symptoms in July, 1976. This was at the peak of the epidemic and when the number of spray teams was accurately known. Questionnaires were administered to 425 spraymen, 86 mixers, and 95 supervisors-i.e., to 72-1% of those selected for interviews. 20% of the supervisors, 38% of the mixers, and 41% of the spraymen gave histories of at least one episode of malathion intoxication (defined as acute illness characterised by four of the following five symptoms: blurred vision, giddiness, nausea, vomiting, or abdominal cramps) during July, 1976. Thus we estimate that there were 2810 workers with at least one episode of pesticide intoxication during July. Since some of the workers who" were ill during July were no longer working and could not be interviewed, these figures probably underestimate the prevalence of disease. 36 malaria spray workers who used D.D.T. instead of malathion during July were interviewed for comparison; none of these men reported any symptoms suggestive of pesticide toxicity.
gramme.
Background Before 1976, D.D.T. and B.H.c. were the primary residual insecticides used in Pakistan for spraying on interior household surfaces where mosquitos rest. Vector resistance to these insecticides increased, and malathion became the primary insecticide in 1976. About 1100
Field Study Staff from the provincial and district malaria programmes observed spray teams during a typical working day and completed a detailed work-practice and symptom checklist on each worker. At the start and at the end of the working day, technicians obtained blood-samples
32
from the same workers to determine cholinesterase activities. Cholinesterase analyses were performed by a modification of the standard method of Michel’ and a colorimetric method which used a tintometer field kit. Cholinesterase activities as determined by the colorimetric method correlated poorly (0-45) with erythrocyte cholinesterase activities .determined by the modified Michel method and even less well (r=0.37) with plasmacholinesterase activities determined by the same technique. The results obtained by the Michel method are used in subsequent calculations. Spraymen and mixers who used brand-3 malathion had the most severely depressed red-cell cholinesterase activities (table i); the average decrease over a single working day was 40-45%. Cholinesterase depression with brand 2 was significantly greater than with brand 1 (t=5.97, p
Occupational
Medicine
EPIDEMIC MALATHION POISONING IN PAKISTAN MALARIA WORKERS MCWILSON WARREN RONALD D. DOBBIN STEVEN MILLER WINNIE R. TEETERS
of Epidemiology and Tropical Diseases, Center for Disease Control, Atlanta, Georgia 30333; National Institute for Occupational Safety and Health, Center for Disease Control, Cincinnati, Ohio 45202; and Pharmacology Laboratory, Technical Service Division, U.S. Environmental Protection Agency, Beltsville, Maryland 20705, U.S.A.
were
employed
in
Punjat
plied as a water-dispersible powder containing approximately 50% malathion and 50% carrier and was mixed in the field. Three formulations of malathion were used in 1976: an American company (brand 1) supplied 5700 tonnes, an Italian chemical company (brand 2) supplied 1000 tonnes, and another Italian company (brand 3) supplied 350 tonnes. with
EDWARD L. BAKER, JR. MATTHEW ZACK JAMES W. MILES LEE ALDERMAN
(7700 workers)
and North-West Frontier Province, the main areas oj malathion usage. Each spray team consisted of 1 mixer, 5 spraymen, and 1 field supervisor. Malathion was sup-
water
Bureaux
Epidemic Pesticide intoxication began to occur in late June, after the start of spraying. Intoxication was more common on Friday and Saturday (at the end of the sixsoon
day working week) than on Sunday (when no spraying place). The symptoms and clinical histories of these patients were consistent with organophosphate-insecticide intoxication;6 some workers experienced burns and rashes after skin contact with the pesticide. Workers using the Italian formulations reportedly had the most severe illnesses. Insecticide poisoning probably led to at least 5 deaths (2 mixers and 3 spraymen). 3 workers in areas where the Italian-formulated pesticide was used died after exposure during only their normal work activities. 2 deaths were reported from areas where the American formulation was used: 1 sprayman died shortly after he consumed food which had been sprayed, but death of a second sprayman was poorly documented. took
In 1976, epidemic organophosphate insecticide poisoning due to malathion occurred among 7500 field workers in the Pakistan malaria control programme. In July, the peak month of the epidemic, it is estimated that there were about 2800 cases. In field studies low red-cell cholinesterase activities were associated with the signs and symptoms of organophosphate insecticide intoxication. Toxicity was seen with 3 different formulations of the insecticide and was greatest with the products containing increased amounts of isomalathion, a toxic malathion degradation product. Poor work practices, which had developed when D.D.T. was the primary insecticide for malaria control, resulted in excessive skin contact with and percutaneous absorption of the pesticide. Airborne malathion concentrations were very low. Implementation of good work practices and proscription of use of the 2 pesticide formulations most contaminated with isomalathion halted the epidemic in September. An extensive training programme and surveillance system for pesticide toxicity preceded 1977 spraying operations.
Summary
INTRODUCTION
regarded as one of the safest organoin general use, and has replaced insecticides phosphorus D.D.T. and benzene hexachloride (B.H.C.) in malaria-control programmes as resistance to these compounds has developed in the Anopheles mosquito.2 Extensive field testing of malathion in malaria programmes in Uganda,3 Nigeria,4 and Central Americas demonstrated relatively little evidence of human toxicity. In the Ugandan and Nigerian studies, symptoms of pesticide intoxication and reduced cholinesterase activities were not encountered. In the Central American study, severe pesticide intoxication developed in 3 spraymen who wore uniforms wet with kerosene solutions of malathion for several days. We describe an epidemic of insecticide intoxication among field workers in the Pakistan malaria control proMALATHION is
METHODS AND RESULTS
Retrospective Questionnaire Survey The staff of the provincial malaria programmes interviewed a random sample (approximately 10%) of the spraymen, mixers, and supervisors in Punjab and NorthWest Frontier Province to estimate the prevalence of pesticide-intoxication symptoms in July, 1976. This was at the peak of the epidemic and when the number of spray teams was accurately known. Questionnaires were administered to 425 spraymen, 86 mixers, and 95 supervisors-i.e., to 72-1% of those selected for interviews. 20% of the supervisors, 38% of the mixers, and 41% of the spraymen gave histories of at least one episode of malathion intoxication (defined as acute illness characterised by four of the following five symptoms: blurred vision, giddiness, nausea, vomiting, or abdominal cramps) during July, 1976. Thus we estimate that there were 2810 workers with at least one episode of pesticide intoxication during July. Since some of the workers who" were ill during July were no longer working and could not be interviewed, these figures probably underestimate the prevalence of disease. 36 malaria spray workers who used D.D.T. instead of malathion during July were interviewed for comparison; none of these men reported any symptoms suggestive of pesticide toxicity.
gramme.
Background Before 1976, D.D.T. and B.H.c. were the primary residual insecticides used in Pakistan for spraying on interior household surfaces where mosquitos rest. Vector resistance to these insecticides increased, and malathion became the primary insecticide in 1976. About 1100
Field Study Staff from the provincial and district malaria programmes observed spray teams during a typical working day and completed a detailed work-practice and symptom checklist on each worker. At the start and at the end of the working day, technicians obtained blood-samples
32
from the same workers to determine cholinesterase activities. Cholinesterase analyses were performed by a modification of the standard method of Michel’ and a colorimetric method which used a tintometer field kit. Cholinesterase activities as determined by the colorimetric method correlated poorly (0-45) with erythrocyte cholinesterase activities .determined by the modified Michel method and even less well (r=0.37) with plasmacholinesterase activities determined by the same technique. The results obtained by the Michel method are used in subsequent calculations. Spraymen and mixers who used brand-3 malathion had the most severely depressed red-cell cholinesterase activities (table i); the average decrease over a single working day was 40-45%. Cholinesterase depression with brand 2 was significantly greater than with brand 1 (t=5.97, p
