724 TRANSACTIONSOF THE ROYAL SOCIETYOF TROPICAL MEDICINE AND HYGIENE. Vol. 66. No. 5. 1972. T R O P I C A L S P L E N O M E G A L Y S Y N D R O M E IN N E W G U I N E A I. N A T U R A L H I S T O R Y G. G. CRANE,* J. VIVIAN W E L L S t AND P. HUDSON,: The Haematology Research Unit, Angau Memorial Hospital, Lae, Territory of Papua and New Guinea, the Institute of Human Biology, Goroka and the Division of Haematology, Prince Henry Hospital, Sydney, New South Wales Introduction The term tropical splenomegaly syndrome refers to a condition of persistent splenomegaly, occurring in the absence of demonstrable underlying disease, which is found in adult inhabitants of m a n y tropical countries (PITNFX, 1968). It has, for example, been reported from the Sudan (~V[OSTAFA, 1965), Nigeria (WATSON-WILLIAMSand ALLAN, 1968), Uganda (MARSDENet al., 1965), Zambia (LOWENTHALet al., 1966), India (CHAuDHURl et al., 1956) and New Guinea (PR¥OR, 1967a; MARSDENet al., 1967); but only from parts of these countries where malaria is or was endemic. The disease has disappeared from some areas where malaria eradication campaigns have been successful (CHAUDHURI et al., 1956), and regression of splenomegaly has been observed in individual Africans given prolonged suppressive courses of the anti-malarial drug proguanil (WATSONWILLIAMSand ALLAN, 1968; SAGOE, 1970; STUIVERet al., 1971 ; LOWENTHALet al., 1971). Thus, there seems litde doubt that malarial infection plays an aetiological r61e in the development of the syndrome. However, the syndrome is not found in all malarious areas, and its prevalence varies widely in different affected populations. Furthermore, the associated features of the disease--lymphocytic infiltration of the hepatic sinusoids, absence of malarial pigment in liver or spleen, and exceptionally high serum IgM concentrations and fluorescent malaria antibody titres, provide grounds for regarding the tropical splenomegaly syndrome as an atypical immune response to malaria (British Medical ffournal, 1969), since these features do not constitute the normal response to malarial parasitaemia in immune adults. Whether the syndrome is produced by an unusual type of malarial infection, giving rise to an abnormal pattern of antigenic stimulation, or is the result of constitutional factors in the affected subjects, has not yet been elucidated. *Present address: Institute of Human Biology of Papua and New Guinea, P.O. Box 60, Goroka. tPresent address: Department of Medicine, Section of Haematology and Immunology, San Francisco Medical Centre, San Francisco, California, 94122. ~:Present address: Institute of Human Biology Field Station, c/o New Tribes Mission, Slate Creek, Via Bulolo. The Haematology Research Unit, Lae, was supported by the Administration of the Territory of Papua and New Guinea and by the WeLlcome Trust. The immunoglobulia determinations were performed by J.V.W. during the tenure of a Medical Postgraduate Research Scholarship from the National Health and Medical Research Council. The authors gratefully acknowledge the assistance of Dr. D. S. Pryor, who gave free access to his records of the subiects of the investigation, and of Professor W. R. Pitney and Professor R. J. Walsh of the University of New South Wales. A further grant to the Institute o f Human Biology by the WeUcome Trust has permitted the recent field work to be undertaken.
G. G. CRANE, J. VIVIAN WELLS AND P. HUDSON
The incidence of the syndrome is particularly high in the Upper Watut Valley of New Guinea. The 3,500 inhabitants, who are known as Watuts, belong to the Kukukuku tribe. They live in villages between 3,300 and 5,200 feet above sea level. Over 60% of adults and children aged 10 years or more have spleens of at least Grade I I I size on the Hackett scale (WHO, 1963). Men and women are equally affected. The distribution of the various grades of splenomegaly remains constant in all age groups above 10 years (PaYoR, 1967a). No cause of splenomegaly unrelated to malaria has been found in this population (PRYOR, 1967C; PITNEY et al., 1968; CLONE, 1971). Malaria is mesoendemic and stable throughout the valley, the predominant species being P. vivax (CRANE and PRYOR, 1971). Among the Watuts splenomegaly is commonly accompanied by anaemia, neutropenla and thrombocytopenia, the severity of which tends to increase with increasing degrees of splenomegaly (PaYoR, 1967b; CaANE, in press). The immunoglobulin pattern is also grossly abnormal (WEr~Ls, 1968; W~.r.LS, 1970; CRANF-et al., 1971). There are, therefore, reasonable grounds for suspecting that, at least when splenomegaly is pronounced, the syndrome may be associated with a reduced life expectancy to which chronic anaemia, increased susceptibility to infections, haemorrhagic tendencies and liability of the spleen to rupture, could all contribute. This longitudinal study of affected Watuts was undertaken to establish whether these factors affect survival in a village setting; and to determine to what extent the tropical splenomegaly syndrome is a progressive disease in these people. Subjects and methods The subjects studied consisted of 99 adult Watuts originally admitted between December 1964 and June 1966 to the Haematology Research Unit, Angau Memorial Hospital, Lae, for investigation. Each had at least Grade I I I splenomegaly when first seen. The results of the original haematological and histological studies have been reported by PAYOR(1967a; 1967b; 1967c) and by PITNEY et al. (1968). The present study included both observations in the Upper Watut Valley and further laboratory investigations in Lae and Sydney. After the subjects returned home they had access to the two aid posts in the valley (located between 1 and 8 hours' walk from their villages), but no special medication was given. Contact was maintained with them by specific enquiry each time their village was visited, and any marked change in their physical condition was recorded whenever they were seen. All subjects in whom follow-up was practicable were re-examined and their state of health assessed in April, 1971. Mortality rates and changes in degree of splenomegaly are derived from this study. 25 of the 99 subjects were persuaded to return to Lae during 1968 for repetition of haematological investigations and for detailed assessment of the course of their disease. They remained in hospital for an average period of 4 weeks, during which time they were given an initial course of chloroqulne (1,500 mg. base) and an anti-helminthic (bephenium hydroxynaphthoate 5 gramme). Subsequently they received chloroquine 300 mg. base weekly, and ferrous sulphate 300 mg. thrice daily. Full blood counts were performed at weekly intervals, using standard techniques (DAclE and LEWIS, 1968). Red cell volume and splenic red cell pool were measured by the method described by PR¥OR (1967b), using autologous 51Cr labelled erythrocytes. Plasma volume was estimated using x3xI labelled human serum albumin, essentially by the method of DACIE and LEwis (1968). serum specimens were collected in Lae, packed in ice and flown to Prince Henry Hospital, Sydney, where determination of serum immunoglobulin concentrations was carried out by radial immunodiffusion (FAHEYand MCKELVEY,1965) using Immunoplates (Hyland Laboratories, California). Results
Mortality The findings from the field survey are summarized in Table I. The series comprised 5 1 males and 48 females, all adults. At the time of their initial admission to hospital
TROPICAL SPLENOMEGALY SYNDROME I N NEW GUINEA
Grade III splenomegaly was present in 17, Grade IV in 35 and Grade V in 47. Three subjects have left the district, and so have been lost to follow-up. The follow-up rate is thus 97%. TABLE I. Results of field follow-up studies on 99 Watuts. Spleen grade
Number of subjects
IV V Total
Untreated and traced
Splenectomy was performed on 21 subjects either at the time of their initial admission to hospital or subsequently; these have consequently been excluded from this study of the natural history of the syndrome. Thus, 75 remained in the series. 27 of these 75, 15 females and 12 males, have died, giving an overall mortality of 36%. The mortality rate was 29% in those presenting with Grade III splenomegaly, 20% in those with IV splenomegaly, but 57% in subjects with Grade V splenomegaly. The number of deaths in this last group is significantly greater than in those with Grade III and IV splenomegaly (P <0-001). The duration of follow-up of the survivors was 60 months to 78 months (mean 70 months) from the date of the first admission to hospital, and the deaths had occurred from 4 to 72 months (mean 37 months) after the same reference point. Only 2 of the 27 deaths occurred in hospital, where the terminal illness could be observed. The patients were both females with Grade V splenomegaly, and both died from septicaemia. In one case death occurred 2 weeks after amputation of a gangrenous lower limb following a dog bite inflicted some weeks previously. In the other it followed apparent resolution of pneumococcal pneumonia. Both pneumococci and Klebsiella pneumoniae were isolated from blood cultures taken from the second patient. The remaining deaths occurred in villages and were observed only by other villagers or by aid post orderlies. 2 women died in labour and another in late pregnancy, 2 months after her discharge from hospital with a haemoglobin concentration of 10.8 g./100 ml. In 7 other cases witnesses supplied similar descriptions of fulminating febrile illnesses, accompanied by prostration and sometimes slight diarrhoea but by no other specific manifestations, and leading to death within 6 to 24 hours. In another case a similar illness was associated with a small haemoptysis or haematemesis. In no other instance did overt bleeding occur as a terminal event, though recurrent minor epistaxes preceded the terminal illness in several cases, and are commonly regarded by the Watuts as an ominous sign. No death seemed attributable to trauma. Retrospective analysis of the hospital records of those who died revealed no data of prognostic value. The mean haemoglobin concentration in hospital had been 9.0 g./100 ml.; that of the survivors with Grade V splenomegaly was 8.5 g./100 ml. at the same time point. Mean leucocyte and platelet counts were comparable in the 2 groups. 3 who have died had total leucocyte counts of less than 2,000/c.mm., but so did 4 subjects who are still alive.
G. G. CRANE~ J. VIVIAN WELLS AND P. HUDSON
M e a n immunoglobulin concentrations were similar in the 2 groups. Clinically it d i d not appear that those who have since died were more severely incapacitated at the time of their first admission. T h u s spleen size is the only prognostic guide, and then only in general terms.
Progress of the disease T h e 25 subjects who returned to Lae for reassessment were not representative o f the original 99. T h e previous inducements of novelty and curiosity were now largely lacking, and in general only those currently experiencing symptoms were prepared to leave their villages. Consequently the 25 included only 1 patient with G r a d e I I I splenomegaly, and her visit was incidental to her husband's admission for an unrelated complaint. By contrast 13 o f the 26 subjects with G r a d e V spleens, who were then still living, were reviewed in hospital.
Spleen size T a b l e I I lists the findings on each admission. I n no case was the degree o f splenomegaly less on the second occasion. 5 o f the 11 subjects who originally presented with TABLE II. Results obtained on 2 hospital admissions of 25 Watuts with splenomegaly.
22 26 24 27 22 14 30 20 35 14 27 12 12 29 15 18 30 20 28 24 18 28 28 24 27 Mean
Initial spleen grade
F F M F F M M M F F M M M M M M F F M F M F F
V IV V V V IV IV V V IV V V V IV IV V V IV IV III IV IV V
*Pregnant on first admission.
+ + + + + +
+ + +
Haemoglobin level on admission (g./100 ml.)
Change in haemoglobin level
6.4* 5.0" 8 "8 7 '6 5 "7 11 "9 12.8 8.4 11 "9 12.4 9"8 9"2 10"0 11-1 11"1 11"1 6"9 11 "4 9-5 13"0 10.4 9"8 10.8 10"4 15.4
9.5 7 "8 11 "6 9"2 7-0 12"2 13"1 8"7 12"2 11 "9 9"0 8"4 9"2 10"1 9"5 9"5 5"1 8-8 6"6 9-8 6"9 6-0 6"9 5-1 9"7
+3"1 +2"8 +2"8 +1 "6 +1 "3 +0"3 +0"3 +0"3 +0"3 -0"5 -0"8 -0"8 -0"8 - 1 "0 - 1 "6 - 1 '6 - 1 "8 --2"6 -2"9 --3 "2 -3"5 - 3 "8 - 3 "9 - 5 "3 - 5 "7
TROPICAL SPLENOMEGALY SYNDROME I N NEW GUINEA
Grade IV splenomegaly now had Grade V spleens, and of the 13 who had Grade V splenomegaly on their first admission, 5 now showed a gross increase in spleen size. Thus in i0 of the 25 subjects further splenic enlargement had occurred.
Haemoglobin concentrations The punctuation of the course of this disease by acute haemolytic episodes has been described elsewhere (HAMILTONet al., 1966; PRYOR, 1967b; CRANE, in press). Such episodes may be initiated by an acute febrile attack, are associated clinically with sudden onset of profound weakness and lethargy of several weeks' duration, marked pallor and slight icterus. Investigations show a disproportionately low haemoglobin concentration for the degree of splenomegaly, a high reticulocyte count, gross erythroid hyperplasia of the bone marrow and hyperbilirubinaemia without bilirubinuria. In 5 of the patients studied the second admission to hospital was precipitated by such an episode, which had already been present for between 2 and 4 weeks at the time of admission. In none of these patients were malaria parasites found in the peripheral blood, and in none was overt iron deficiency or megaloblastic anaemia present. On routine management rises in haemoglobin concentration of at least 2 g./100 ml. occurred within 3 weeks, and were paralleled by falls in serum bilirubin levels to within the normal range. A similar presentation had been observed in another 5 of these subjects on their first admission. By the time of discharge all had achieved a steady haemoglobin concentration. This final figure more accurately reflects their normal state, and these values on discharge are the ones shown in Table II, and which are compared in the subsequent presentation. 11 subjects had substantially lower haemoglobin concentrations on their second admission, the reduction ranging from 1.6 to 5-7 g./100 ml. These 11 subjects included 9 of the 10 who also showed a significant increase in spleen size. The haemoglobin level in 4 subjects was over 1.5 g./100 ml. higher than on the first admission; in no case was this accompanied by a demonstrable decrease in spleen size. The 2 who showed the greatest increases (3.1 and 2-8 g./100 ml.) had been in the last trimester of pregnancy when first admitted, and this had presumably contributed to their anaemia on that occasion. I f one excludes these 2 subjects because of this complicating factor, the fall of 1.4 g./100 ml. in mean haemoglobin level of the remaining 23 is statistically significant (e <0.02). Leucocyte and platelet counts Total leucocyte and platelet counts were similar on both admissions, there being no significant differences between mean values on the two occasions. However, those in whom there had been further splenic enlargement had a significantly lower mean neutrophil count on the second admission (1,490 cf 2,400/c.mm.), whereas for the remainder the corresponding values were 2,600 and 2,850/c.mm. Blood volume estimations The results for the 15 subjects on whom these determinations were performed on both admissions are set out in Table III. Total red cell volume increased and decreased in equal numbers of subjects, the mean values for the 2 admissions being identical. The splenic red cell pool was smaller on the second admission in only 3 subjects. It had expanded in 12, in 7 of whom the increase exceeded 10% of the total red cell volume. Increases in plasma volume were matched in both number and magnitude by decrcases, the mean values differing by only 1.5 ml./kg. However, the combination of a higher spleen grade and a lower haemoglobin concentration on the second admission was
G. G. C R A N E , ~. V I V I A N W E L L S A N D P . H U D S O N
regularly associated with marked increases in both splenic red cell pool and plasma volume--these being responsible for the drop in haemoglobin level. TABLE III. Progress blood volume estimations and serum immunoglobulin levels in 19 Watuts with tropical splenomegaly syndrome. Red cell and plasma volumes in rni./kg., splenic pool as percentage of total red ceU volume, inununoglobulin concentrations in rag./100 ml.
Blood volume estimations First Admission
Splenic I Plasma pool % volume
Serum immtmoglobulin levels
Second Admission Total RCV
Splenic Plasma pool % volume
38 50 55 73
*Subject with significantly larger spleen and lower haemoglobin level on second admission.
Immunoglobulin levels Serum was available from 14 subjects for determination of immunoglobulin levels. Individual and mean values of IgG, IgM and IgA are listed in Table III. Serum IgG and IgA concentrations showed no significant alteration in the interval between admissions. The mean IgM concentration had increased from 1,330 to 1,710 mg./100 ml., hut this difference is not statistically significant. In 4 subjects increases in IgM level of more than 1,000 rag./100 nil. were observed; but alterations of this magnitude were not regularly associated with an increase in spleen size, with a substantial fall in haemoglobin level, or with expansion of plasma volume. General health As in assessing the significance of lowered haemoglobin concentrations, so it is also necessary in the clinical assessment of incapacity to make a distinction between 2 different clinical situations: (1) a gradual increase in incapacity progressing to complete invalidism, associated with increasing splenomegaly and anaemia, failure of symptoms to improve appreciably even with hospital management, inability to cope with incidental
TROPICAL SPLENOMEGALY SYNDROME I N NEW GUINEA
infections, epistaxes and eventual cachexia; and (2) incapacity which may be of equal severity but of more sudden onset and shorter duration, associated with evidence of acute haemolysis, and remitting spontaneously within a few weeks. The first situation is exemphfied by the 10 subjects in the present series who showed both an increase in spleen grade and a significant lowering of haemoglobin concentration on their second admission. The second situation is illustrated by the haematological findings obtained on 4 admissions of i patient, listed in Table IV. He was asymptomatic on the first admission, but on each subsequent occasion presented with symptoms of severe weakness of several weeks' duration. His spleen did not change in size during 3 years of dose observation. Plasma volume and immunoglobulin concentrations did not alter. On each occasion that weakness precipitated his admission, a low haemoglobin level due to a decrease in red cell mass was found. Peripheral blood and bone marrow examination revealed no abnormality other than reticulocytosis and high serum bilirubin concentration: thus increased haemolysis seemed to be solely responsible for his symptoms. Malaria parasites were never found. Haematological improvement occurring in hospital was paralleled by clinical remission on each occasion. TABLEIV. Results of haematological investigations on 1 subject with Grade V splenomegaly
during 4 admissions between 1965 and 1968. May 1965
Initial Hb (g./100 ml.)
Initial reticulocyte count
Total red cell volume (ml./kg.)
Plasma volume (ml.) (ml./kg.)
Serum IgG (rag./100 ml.) IgM (rag./100 ml.) IgA (mg./100 ml.)
1,800 2,150 179
1,440 2,390 147
1,750 2,500 188
1,320 2,600 156
Initial leucocyte count per c.mm. Hb. on discharge (g./100 ml.)
Clinical experience with gross splenomegaly in other circumstances would cause one to anticipate increased susceptibility to infections, haemorrhagic episodes and traumatic rupture of the spleen in the patients described here. It was therefore remarkable that some epistaxes, often late in the clinical course, were the only bleeding manifestations observed. Gastrointestinal haemorrhage was not seen, perhaps reflecting the relative normality of liver function (M~sDEIq et al., 1965; CRANE, 1971), and the absence of gross elevation of portal venous pressure (PRYOR, 1967c). Traumatic rupture of the spleen has not yet been observed by us in this syndrome.
G. G. CRANE~ J. VIVIAN WELLS AND P. HUDSON
Apart from persistent leg ulcers, to the maintenance of which infection is only a contributory factor, skin infections did not appear to be a significant problem. The major hazard to health appeared to be overwhelming bacterial infection as manifested by the 2 terminal septicaemias and 8 apparently similar village deaths. Observation of the leucocyte counts of other subjects with splenomegaly who have developed pneumococcal pneumonia while in hospital has shown that the expected neutrophil response to this infection is often impaired. Thus the failure to mobilize cellular defences prompdy, together with initially low numbers of circulating neutrophils, may be solely responsible. However, one cannot exclude a degree of immune paresis. Watuts with splenomegaly show impaired specific primary antibody responses after stimulation with Salmonella flagellin and influenza antigens (CRANE et al., in press). Thus their reserve capacity to produce specific antibody in response to non-malarial challenges is questionable, as is also the effectiveness of their excess circulating IgG and IgM in the control of infections. There may be, in addition, an increased risk of death from anaemia itself during acute haemolytic episodes, either because of their greater frequency or severity in those with the largest spleens, or through bone marrow depression from some complication such as secondary folate deficiency. The relative frequency and severity of such episodes in subjects with different grades of splenomegaly is not known, nor is it clear what factors determine the rate of haemolysis at any one time. The combination of splenomegaly, increased serum IgM concentrations and hepatic sinusoidal lymphocytosis is characteristic of the tropical splenomegaly syndrome. However, the degree of hepatic sinusoidal lymphocytosis does not correlate with the spleen size, and this finding may occur in the absence of splenomegaly or vice versa (MARSDEN et al., 1967). Similarly, individual subjects without splenomegaly may have very high serum IgM levels, while some with massive splenomegaly show only a modest elevation (CRANE et al., 1971). The relationship between spleen grade and the sizes of splenic red cell pool and plasma volume is subject to equal variability when individual cases are considered (CRANE,in press). Thus it seems that spleen size, splenic red cell pool, plasma volume and serum IgM concentrations behave to some extent as independent variables which alter at different rates and at different phases of the illness in individual subjects. However, as all are integral components of the syndrome, a marked change in any one measurement probably indicates progression of the disease process. If this is so, then the majority of the subjects studied show evidence of a progressive disease. However neither blood counts, blood volume estimations nor serum immunoglobulin estimations were selectively useful in predicting clinical progression of the syndrome or death. The demonstration of increased mortality rate associated with Grade V splenomegaly, added to the epidemiological evidence of a constant frequency distribution of different spleen sizes from the second to the fifth decade of life in the Watuts, gives further evidence of the disorder being progressive. If spleen size were determined before the age of 10 and remained unchanged throughout life, there would be a decrease in the frequency of Grade V spleens in older age groups, resulting from the increased mortality. If the individual spleen fluctuated in size appreciably from time to time after the first decade of life, the numbers enlarging and regressing might balance each other, thus preserving the frequency distribution at different ages. However, none of the subjects studied in hospital had a lower grade of splenomegaly when subsequently re-examined, and so this hypothesis appears unlikely. Thus only if the syndrome is generally progressive throughout life, with increased mortality in the Grade V spleen group, will the constant frequency distribution be maintained with age in accord with our data.
TROPICAL SPLENOMEGALYSYNDROME IN NEW GUINEA
Summary The course of the tropical splenomegaly syndrome has been observed for periods of up to 6~ years in 75 adults living in the Upper Watut Valley of New Guinea~ During this time there were 27 deaths, 2 from septicaemia and another 8 from similar fulminating febrile illnesses. The mortality rate in those with Grade V splenomegaly was 57%, almost 3 times that of the remainder. Serial hospital assessment of 26 subjects demonstrated progression of the disease, characterized by further enlargement of the spleen and a fall in haemoglobin concentration in 9; increases in splenic red cell pool, in plasma volume and in serum IgM concentration were sometimes, but not invariably, associated. In none of the total group of 75 subjects was a decrease in spleen size observed. Thus the natural history of the tropical splenomegaly syndrome is that of a progressive disease with a high mortality in the fully developed case. Periodic fluctuations in the clinical severity of the disorder are frequently seen and are largely related to the occurrence of episodes of acute haemolysis; however, spontaneous remission has not been observed. REFERENCES BRITISH MEDICALJOURNAL(1969). Br. med. J., 4, 4. CHAUDHURI,R. N., SAHA, T. K., BASU, S. P., MUKHERJEE,A. M. & CHAUDHURI,i . N. R. (1956). Indian ~. med. Res., 44, 305. CRANE, G. G. (1971). The aetiology and mechanisms of chronic hypervolaemia associated with tropical splenomegaly syndrome in Watut Valley natives. Doctoral thesis, Faculty of Medicine, University of New South Wales. - - . Anaemia in the Upper Watut Valley of New Guinea. In Press. - & PRYOR, D. S. (1971). Trans. R. Soc. trop. Med. Hyg., 65, 315. , PITNEY, W. R., HOBBS,J. R. & GUNN, C. (1971). Ibid., 65, 795. , ROWLEY, M. J., WARBURTON, M. F. & MACKAY, I. R. Humoral immune responses in the tropical splenomegaly syndrome in New Guinea. In press. DACIE, J. V. & LEWIS, S. M. (1968). Practical Haematology. 4th Ed. London: Churchill. FAHEY, J. L. & MCKELVEY, E. M. (1965). J. Immunol., 04) 84. HAMILTON,P. J. S., GEBBIE,D. A. M., HUTT, i . S. R., LOTHE, F. & WILKS, N. E. (1966). Br. med. J., 2, 548. LOWENTHAL, M. N., HAMILTON,P. J. S., HUTT, M. S. R. & WILKS, N. E. (1966). Cent. Aft. J. Med., 12, 99. , O'RIORDAN, E. C. & HUTT, M. S. R. (1971). Br. med. J., 1,429. MARSDEN, P. n . , CONNOR, n . n . , VOLLER, A., KELLY, A., SCHOFIELD, F. D. & HUTT,
M. S. R. (1967). Bull. Wld Hlth Org., 36, 901. , HUTT, i . S. R., WILKS, N. E., VOLLER, A., BLACKMAN,V., SHAH, K. K., CONNOR, D. H., HAMILTON,P. J. S., BANWELL,J. G. & LtINN, H. F. (1965). Br. med. J., 1, 89. MUSTAFA, D. (1965). J. trop. &fed. Hyg., 68, 183. PITNEY, W. R. (1968). Trans. R. Soc. trop. i~led. Hyg., 62, 717. ~ , PRYOR, D. S. & T ~ T SMITH, A. (1968). J. Path. Bact., 95, 417. I~YOR, D. S. (1967a). Quart. J. Med., 36, 321. (1967b). Ibid., 36, 337. (1967c). Br. reed. J.~ 3, 825. SAGOE, A-S. (1970). Ibid., 3, 378. STUIVER, P. C., ZIEGLER,J. L., WooD, J. B., MORROW, R. H. & HtrrT, M. S. R. (1971). Ibid., I, 426. WORLD HEALTHORGANIZATION(1963). Terminology of Malaria and of Malaria Eradication. Geneva: WHO. WATSON-WILLIAMS,E. J. & ALLAN, N. C. (1968). Br. med. J., 4, 793. WELLS, J. V. (1968). Clin. exp. Immunol., 3, 943. - (1970). Trans. R. Soc. trop. Med. Hyg., 64, 531.