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Epidemiology of sleeping sickness
136 TRANSACTIONSOF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE. Vol. 60. No. 1. 1966.
CORRESPONDENCE To the Editor LABELLING MOSQUITOESWITH RADIO-ACTIVEIODINE, 1~1I SiR,--Radio-active isotopes have been used to label insects for studies of their flight range and dispersal rates, a2p, a beta emittor, has been most commonly employed, but its detection in insects is time-consuming and complicated. We wish to report the successful use of x3xI, a gamma emittor, for labelling Culex pipiens fatigans, a common househaunting mosquito in many tropical countries. I n a first series of experiments, larvae of C. p. fatigans were reared in water containing N a m I in tracer amounts. As the larvae grew, their uptake of iodine increased steadily. I n a typical experiment, in which 50 microcuries of Na~SlI were added to 4 litres of water containing 1000 larvae, the last instar larvae contained about 100 cpm per individual as measured in a conventional well scintillation counter. The larvae had been exposed for 10 days. However, the level of radio-activity in the pupae dropped to half and the adults, soon after emergence, had only about 20 cpm per individual. The biological half-life in an adult mosquito was about 6 days. I n a second series of experiments, adult mosquitoes aged 2-3 days were kept in cages and 50 ml. of 5% glucose solution containing 200 microcuries of NalSXI were provided as food. After 4 days the average radio-activity was 10,590 clam for females (SD = 1070) and 5980 cpm for males (SD = 548). The amount of radio-activity in the mosquitoes remained nearly constant for 2 days after the solution containing the isotope was removed. I n a supplementary experiment, in which the radio-active food was provided for only 2 days, the variation in radio-activity among the mosquitoes was larger. The mosquitoes of the second series were dissected into head, thorax, abdomen, legs and wings. The amount of radio-activity in each part was measured. T h e distribution of radio-activity was as follows--head 11%; thorax 29%; abdomen 18%; legs 37%; and wings 7%. No effects on the mortality and morphology of the mosquitoes were observed in these experiments. T h e procedures described are simple to apply. We would recommend the second method, using adults, as a practical means of marking mosquitoes for flight range and dispersal studies. We are, etc., L. GARBY. M. YASUNO. Y. PHURIVETHAYA. T h e Bangkok Faculty of Tropical Medicine, University of Medical Sciences, Bangkok, Thailand. 15 October, 1965.
EPIDEMIOLOGY OF SLEEPING SICKNESS SIR,--Dr. K. C. WiUett (Transactions, 1965, 59, 374) has lucidly described the now generally accepted view that Trypanosoma gambiense and T. rhodesiense are variants of one species of trypanosome which can infect man and certain animals, and which differs from T. brucd only in that the latter is restricted to animals; the lesser virulence of T. gambiense is an adaptation to its main host, man, whereas the main hosts of the more virulent T. rhodesiense and the sole hosts of T. brucei are animals. This view is consistent with many features of the epidemiology of sleeping sickness but does not by itself explain the limitation
CORRESPONDENCE
137
of human T. rhodesiense infection to certain loci. As far as is known T. rhodesiense and T. brucei infections in animals are identical so that the two trypanosomes would be expected to spread through animals until their distributions are equal but, judging from the occurrence of human infection, this is not the case. Various explanations have been advanced. The suggestion of Warrington YoPa~ and his colleagues (1930) that T. rhodesiense would lose its infectivity to man when transmitted through animals for any length of time was disproved by the Tinde experiment (FAIm3AIRNand BURTT, 1964). CULWICKet al. (1951) postulated hybridization between T. brucei and T. rhodesiense in which infectivity to man might be lost. ASHCROFr (1963) suggested the possibility of mixed strains of T. brucei and T. rhodesiense and that T. rhodesiense might become so diluted in animals by the preponderance of T. brucei that infectivity to man would, in effect, be lost unless reinforced by T. rhodesiense from human infection; "triple contact" between man, tsetse fly and animal reservoir may be necessary to sustain an endemic focus. Other explanations are possible and although this epidemiological pattern cannot be easily solved it is of great interest because it is unique among the zoonoses. I am, etc., M. T. ASHCROFT. Medical Research Council, Epidemiological Research Unit, University of the West Indies, Jamaica. 3 November, 1965 REFERENCES
ASHCROFT, M. T. (1963). ft. trop. Med. Hyg., 66, 133. CULWlCK, A. T . , FAIRBalRN,H. & CULWlCK,R. E. (1951). ,'inn. trop. Med. Parasit., 45, 11. FAIRBAIRN, H. & BURTT, E. (1964). Ibid., 41, 26. YORKE, W., ADAMS, A. R. D. & MURGaTROYD, F. (1930). Ibid., 24, 115.
THE ANAEMIA OF KWASHIORKOR IN UGANDa
SIR,--We have read with interest the paper by ALLENand DEAN (1965) on the anaemias of kwashiorkor, and should like to make the following comments. We stated that the erythroid hypoplasia of marasmus and kwashiorkor is of two distinct types. One type develops 1-2 weeks after admission to hospital, is associated with infection, and has giant proerythroblasts in the marrow. It remits spontaneously or when the infection clears or is treated. Some of the reduction in haemoglobin is pe,rhaps due to haemodilution, although this is not easy to establish (WATERLOWet al., 1960). The other type develops much later when the patients are clinically better and serum proteins are normal, and has no giant proerythroblasts in the marrow; it is not associated with infection, does not remit spontaneously and, unless treated with riboflavine or prednisone, is usually fatal. We suggested that these deaths might be due to upsets in corticosteroid metabolism (KoNDI et al., 1962a; KONDI et al., 1962b; K o ~ I et al., 1963; FoY et al., 1961; KHO-LIEN-I~NG, 1957; KHo-LIEN-K~NG and T U M ~ E ~ , 1960). Similar findings have been reported by NEAME and NaUDE (1961). Since the presence of giant proerythroblasts is considered important in differentiating between these two types ofaplasia it is surprising that Allen and Dean do not mention them. The average stay in hospital of the patients reported by Alien and Dean was 17 days; in our patients it was 1-5 months and the marrow samples were taken weekly or sometimes more often. Since the second type of hypoplasia is unlikely to develop in 17 days, it is possible that it was missed in the Allen and Dean patients. Regarding proteins, we said ( F o Y e t al., 1958) that the place they occupied in the aetiology of the anaemias of marasmus and kwashiorkor was uncertain, and we gave figures to show that in marasmus and kwashiorkor the haemoglobin level remained unchanged during dietary treatment unless a specific haematinic for the anaemia was also given, although the serum proteins returned to 'normal. I n our experience, the anaemias of marasmus and kwashiorkor (mean haemoglobin 10-0 g. per 100 ml., range 7.2-13.5) are not generally as gross as the megaloblastic and iron-deficiency anaemias of the tropics in which the mean haemoglobin levels are 5.2 g.
CORRESPONDENCE To the Editor LABELLING MOSQUITOESWITH RADIO-ACTIVEIODINE, 1~1I SiR,--Radio-active isotopes have been used to label insects for studies of their flight range and dispersal rates, a2p, a beta emittor, has been most commonly employed, but its detection in insects is time-consuming and complicated. We wish to report the successful use of x3xI, a gamma emittor, for labelling Culex pipiens fatigans, a common househaunting mosquito in many tropical countries. I n a first series of experiments, larvae of C. p. fatigans were reared in water containing N a m I in tracer amounts. As the larvae grew, their uptake of iodine increased steadily. I n a typical experiment, in which 50 microcuries of Na~SlI were added to 4 litres of water containing 1000 larvae, the last instar larvae contained about 100 cpm per individual as measured in a conventional well scintillation counter. The larvae had been exposed for 10 days. However, the level of radio-activity in the pupae dropped to half and the adults, soon after emergence, had only about 20 cpm per individual. The biological half-life in an adult mosquito was about 6 days. I n a second series of experiments, adult mosquitoes aged 2-3 days were kept in cages and 50 ml. of 5% glucose solution containing 200 microcuries of NalSXI were provided as food. After 4 days the average radio-activity was 10,590 clam for females (SD = 1070) and 5980 cpm for males (SD = 548). The amount of radio-activity in the mosquitoes remained nearly constant for 2 days after the solution containing the isotope was removed. I n a supplementary experiment, in which the radio-active food was provided for only 2 days, the variation in radio-activity among the mosquitoes was larger. The mosquitoes of the second series were dissected into head, thorax, abdomen, legs and wings. The amount of radio-activity in each part was measured. T h e distribution of radio-activity was as follows--head 11%; thorax 29%; abdomen 18%; legs 37%; and wings 7%. No effects on the mortality and morphology of the mosquitoes were observed in these experiments. T h e procedures described are simple to apply. We would recommend the second method, using adults, as a practical means of marking mosquitoes for flight range and dispersal studies. We are, etc., L. GARBY. M. YASUNO. Y. PHURIVETHAYA. T h e Bangkok Faculty of Tropical Medicine, University of Medical Sciences, Bangkok, Thailand. 15 October, 1965.
EPIDEMIOLOGY OF SLEEPING SICKNESS SIR,--Dr. K. C. WiUett (Transactions, 1965, 59, 374) has lucidly described the now generally accepted view that Trypanosoma gambiense and T. rhodesiense are variants of one species of trypanosome which can infect man and certain animals, and which differs from T. brucd only in that the latter is restricted to animals; the lesser virulence of T. gambiense is an adaptation to its main host, man, whereas the main hosts of the more virulent T. rhodesiense and the sole hosts of T. brucei are animals. This view is consistent with many features of the epidemiology of sleeping sickness but does not by itself explain the limitation
CORRESPONDENCE
137
of human T. rhodesiense infection to certain loci. As far as is known T. rhodesiense and T. brucei infections in animals are identical so that the two trypanosomes would be expected to spread through animals until their distributions are equal but, judging from the occurrence of human infection, this is not the case. Various explanations have been advanced. The suggestion of Warrington YoPa~ and his colleagues (1930) that T. rhodesiense would lose its infectivity to man when transmitted through animals for any length of time was disproved by the Tinde experiment (FAIm3AIRNand BURTT, 1964). CULWICKet al. (1951) postulated hybridization between T. brucei and T. rhodesiense in which infectivity to man might be lost. ASHCROFr (1963) suggested the possibility of mixed strains of T. brucei and T. rhodesiense and that T. rhodesiense might become so diluted in animals by the preponderance of T. brucei that infectivity to man would, in effect, be lost unless reinforced by T. rhodesiense from human infection; "triple contact" between man, tsetse fly and animal reservoir may be necessary to sustain an endemic focus. Other explanations are possible and although this epidemiological pattern cannot be easily solved it is of great interest because it is unique among the zoonoses. I am, etc., M. T. ASHCROFT. Medical Research Council, Epidemiological Research Unit, University of the West Indies, Jamaica. 3 November, 1965 REFERENCES
ASHCROFT, M. T. (1963). ft. trop. Med. Hyg., 66, 133. CULWlCK, A. T . , FAIRBalRN,H. & CULWlCK,R. E. (1951). ,'inn. trop. Med. Parasit., 45, 11. FAIRBAIRN, H. & BURTT, E. (1964). Ibid., 41, 26. YORKE, W., ADAMS, A. R. D. & MURGaTROYD, F. (1930). Ibid., 24, 115.
THE ANAEMIA OF KWASHIORKOR IN UGANDa
SIR,--We have read with interest the paper by ALLENand DEAN (1965) on the anaemias of kwashiorkor, and should like to make the following comments. We stated that the erythroid hypoplasia of marasmus and kwashiorkor is of two distinct types. One type develops 1-2 weeks after admission to hospital, is associated with infection, and has giant proerythroblasts in the marrow. It remits spontaneously or when the infection clears or is treated. Some of the reduction in haemoglobin is pe,rhaps due to haemodilution, although this is not easy to establish (WATERLOWet al., 1960). The other type develops much later when the patients are clinically better and serum proteins are normal, and has no giant proerythroblasts in the marrow; it is not associated with infection, does not remit spontaneously and, unless treated with riboflavine or prednisone, is usually fatal. We suggested that these deaths might be due to upsets in corticosteroid metabolism (KoNDI et al., 1962a; KONDI et al., 1962b; K o ~ I et al., 1963; FoY et al., 1961; KHO-LIEN-I~NG, 1957; KHo-LIEN-K~NG and T U M ~ E ~ , 1960). Similar findings have been reported by NEAME and NaUDE (1961). Since the presence of giant proerythroblasts is considered important in differentiating between these two types ofaplasia it is surprising that Allen and Dean do not mention them. The average stay in hospital of the patients reported by Alien and Dean was 17 days; in our patients it was 1-5 months and the marrow samples were taken weekly or sometimes more often. Since the second type of hypoplasia is unlikely to develop in 17 days, it is possible that it was missed in the Allen and Dean patients. Regarding proteins, we said ( F o Y e t al., 1958) that the place they occupied in the aetiology of the anaemias of marasmus and kwashiorkor was uncertain, and we gave figures to show that in marasmus and kwashiorkor the haemoglobin level remained unchanged during dietary treatment unless a specific haematinic for the anaemia was also given, although the serum proteins returned to 'normal. I n our experience, the anaemias of marasmus and kwashiorkor (mean haemoglobin 10-0 g. per 100 ml., range 7.2-13.5) are not generally as gross as the megaloblastic and iron-deficiency anaemias of the tropics in which the mean haemoglobin levels are 5.2 g.