706 Eaton: Amebiasis Canad. Med. Ass. J. Oct. 12, 1968, vol. 99 Amebiasis in Northern Saskatchewan: Epidemiological Considerations R. D. P. EATON, M.B., Ch.B., R.T.M.&H., D.P.H.,* Macdonald College P.O., Que. AMEBIASIS was first recognized as a cause of morbidity and mortality in the area in July 1959, when an elderly male Indian from the Island Lake reserve died of intestinal per- foration in University Hospital, Saskatoon. Post¬ mortem examination revealed an amebic ulcera¬ tion of the large bowel with perforation. Al¬ though it was not recognized until 1967 when postmortem tissues from a 2-year-old child were reviewed, a second death from amebic colitis with perforation occurred in August 1960, also in a resident of the Island Lake reserve. The first case to be recognized clinically oc¬ curred in 1961 when the 32-year-old son of the first patient mentioned above was admitted to University Hospital with symptoms suggestive of perforation. He survived following a defunc- tioning ileostomy and specific antiamebic therapy with emetine hydrochloride and diiodo- hydroxyquinoline (Diodoquin). This man's wife and an elderly woman from the same reserve suffered from amebic colitis the following month and were treated for it by a local practi¬ tioner who was aware of the disease in that vicinity. Two months later the first case of amebic liver abscess occurred in a 40-year-old man who lived on the edge of Onion Lake reserve some 30 miles to the south of the Island Lake re¬ serve. We have not proved a direct connection in this case. From the records the definitive diagnosis of amebiasis apparently was not made at this time and the patient was treated by open drainage; no amebicides other than oxytetra- cycline (Terramycin) were given. The man sur¬ vived but had a relapse some five months later. On this occasion, after further operative drain¬ age which liberated about a litre of pus, he was given chloroquine and it is evident that the true nature of the infection was then appre- ciated. He recovered and had no further re- lapses. For a period afterwards no diagnosis of amebic disease is recorded in this area (prob¬ ably because of the departure of the physician who had been involved in the early cases). It ?Medical Officer, Medical Services Branch, Department of National Health and Welfare. Present address: Institute of Parasitology, McGill Uni¬ versity, Macdonald College P.O., Quebec. Reprint requests to: Dr. R. D. P. Eaton, Institute of Parasitology, McGill University, Macdonald College P.O., Quebec. Gravelled high way Trail I ft 1 Indian Reserve Scale 1 = 8m.approx. v ,J|B,>V,,3, Fig. 1..Map of area showing location of Indian re- serves (I.R.) was not until about two years later, in 1963, that amebic disease was again reported (possibly because of the arrival of a practitioner with tropical experience). The next two cases were in related individuals, both living in a branch of the Island Lake reserve about six miles north of the main reserve. Not until the end of 1963 was the first patient described from the Loon Lake reserve, but since that time more than half of the cases have come from this reserve. Loon Lake is approximately 20 miles east of Island Lake (Fig. 1). The sudden notification of many cases of amebic disease to the Saskatchewan Depart¬ ment of Health was received with some scepticism. The physician at Loon Lake, Dr. Frank Scott, provided a dozen sera from pa¬ tients who he said had suffered from amebic
Amebiasis in Northern Saskatchewan:Epidemiological Considerations
R. D. P. EATON, M.B., Ch.B., R.T.M.&H., D.P.H.,* Macdonald College P.O., Que.
AMEBIASIS was first recognized as a causeof morbidity and mortality in the area in
July 1959, when an elderly male Indian fromthe Island Lake reserve died of intestinal per-foration in University Hospital, Saskatoon. Post¬mortem examination revealed an amebic ulcera¬tion of the large bowel with perforation. Al¬though it was not recognized until 1967 whenpostmortem tissues from a 2-year-old child were
reviewed, a second death from amebic colitiswith perforation occurred in August 1960, alsoin a resident of the Island Lake reserve.
The first case to be recognized clinically oc¬
curred in 1961 when the 32-year-old son of thefirst patient mentioned above was admitted toUniversity Hospital with symptoms suggestiveof perforation. He survived following a defunc-tioning ileostomy and specific antiamebictherapy with emetine hydrochloride and diiodo-hydroxyquinoline (Diodoquin). This man's wifeand an elderly woman from the same reserve
suffered from amebic colitis the following monthand were treated for it by a local practi¬tioner who was aware of the disease in thatvicinity.Two months later the first case of amebic
liver abscess occurred in a 40-year-old man wholived on the edge of Onion Lake reserve some30 miles to the south of the Island Lake re¬
serve. We have not proved a direct connectionin this case. From the records the definitivediagnosis of amebiasis apparently was not madeat this time and the patient was treated by opendrainage; no amebicides other than oxytetra-cycline (Terramycin) were given. The man sur¬
vived but had a relapse some five months later.On this occasion, after further operative drain¬age which liberated about a litre of pus, he was
given chloroquine and it is evident that thetrue nature of the infection was then appre-ciated. He recovered and had no further re-
lapses.For a period afterwards no diagnosis of
amebic disease is recorded in this area (prob¬ably because of the departure of the physicianwho had been involved in the early cases). It
?Medical Officer, Medical Services Branch, Department ofNational Health and Welfare.Present address: Institute of Parasitology, McGill Uni¬versity, Macdonald College P.O., Quebec.Reprint requests to: Dr. R. D. P. Eaton, Institute ofParasitology, McGill University, Macdonald College P.O.,Quebec.
Gravelled high wayTrail
I ft 1 Indian Reserve
Scale 1 = 8m.approx.
v ,J|B,>V,,3,
Fig. 1..Map of area showing location of Indian re-serves (I.R.)
was not until about two years later, in 1963, thatamebic disease was again reported (possiblybecause of the arrival of a practitioner withtropical experience). The next two cases werein related individuals, both living in a branchof the Island Lake reserve about six miles northof the main reserve. Not until the end of 1963was the first patient described from the LoonLake reserve, but since that time more thanhalf of the cases have come from this reserve.Loon Lake is approximately 20 miles east ofIsland Lake (Fig. 1).The sudden notification of many cases of
amebic disease to the Saskatchewan Depart¬ment of Health was received with some
scepticism. The physician at Loon Lake, Dr.Frank Scott, provided a dozen sera from pa¬tients who he said had suffered from amebic
disease and these were sent for confirmation ofthe diagnosis to the Communicable DiseaseCenter, Atlanta, Georgia. Only then did theDepartment of Health give credence to the re¬
ports. Howevfer, following upon this confirma¬tion and spurred on perhaps by yet anotheramebic death in a 60-year-old woman (residingclose to the Onion Lake reserve but being bybirth and family connections an Indian from theIsland Lake band) an investigation waslaunched.1 In this the author was deputed toassist Professor E. Meerovitch of the Instituteof Parasitology, McGill University, MacdonaldCollege. The findings of this survey have beenpublished2 and revealed an infection with E. his¬tolytica of 32%, which, on a single sample sur¬
vey, is indeed high. Perhaps the most disturbingfinding, however, was that of the 172 persons in¬vestigated in the survey, no less than 8% ap¬peared to be suffering from acute dysentery ofamebic origin, for which at that time they werenot seeking treatment.The public health significance of the findings
of this survey has been published.1 As notedin both these papers,1, 2 the conditions of sanita-tion on all the reserves left a great deal to bedesired, while sanitary arrangements at a sundance in August 1964, attended by some 500 to600 Indians from neighbouring reserves, pro¬vided optimal conditions for transmission ofenteric disease: (a) complete absence of anyform of toilet arrangements, (b) dependencefor water on the marshy edge of a lake, (c)sleeping together, about 10 to a tent, (d) foodlying on the open ground, and (e) flies anddogs everywhere. The reason why the diseasewas not immediately spread far and wide in theneighbouring reserves remains a mystery. How¬ever, several cases occurring subsequently, fromareas with no other record of the disease, can bedirectly connected with attendance at the 1964sun dance. One death occurred within the nexttwo months in an older man who had been atthe sun dance as a visitor.a subsequent surveyin his home reserve failed to reveal any furtherinfections. A fifth Island Lake reserve residentwho had also attended the August sun dancedied at the end of 1964.
Projects and MethodsOn the basis of the accumulated evidence of
widespread amebic infection, a poor publichealth situation and an affected populationwhose numbers were small enough to makepossible a definitive attack on the problem, thefederal authorities instituted immediate meas¬ures in an attempt to control the outbreak, toprevent its further spread and to provide
prophylactic and curative therapy for thosealready known to be involved. During, the nextthree years the following measures (althoughnot necessarily in the order in which they are
reported here) were undertaken, with amebiasiscontrol as the important if not their solepurpose.An amebiasis research project, including a
physician, a full-time public health nurse andassistance from other nursing and ancillary staffas required, was set up within the MedicalServices Branch of the Department of NationalHealth and Welfare. From time to time the aimsof this project included: (1) aid to other govern-mentally assisted research projects related toamebiasis; (2) liaison with research and treat¬ment facilities at Saskatoon University Hospital;(3) a determination of the present extent of themedical problem; (4) an extended survey in theSaskatchewan region to define the area whereE. histolytica appeared to be established as a
pathogen and/or a commensal; (5) case-finding;(6) prophylactic mass medication; (7) publichealth education of the affected populations.
Substantial funds administered by the IndianAffairs Branch were made available for the im¬provement of housing. Twenty-six new houseswere constructed on the Loon Lake reserve
(population approximately 350) and 12 newhouses on the Island Lake reserve (population250). Pipe-borne water and central washing,bathing and toilet facilities were made avail¬able on Loon Lake reserve. The Loon Lake andIsland Lake reserves were supplied withelectricity.
In the village, surrounded as it is by the LoonLake Indian reserve, the local population de¬veloped great concern not only for itself, butfor the seasonal tourist population, because LoonLake is a popular summer resort. The villagearranged for replacement of the wells, water-wagon supply and privy disposal arrangementsby the installation of a pipe-borne water supplyand a complete sewage disposal system. Thewater and sewer arrangements for the LoonLake reserve area were included in the initialplanning and built in conjunction with this newdevelopment.Three major mass medication programs were
attempted, but there were no lasting benefits.The first of these was launched in November1964. The entire populations of the Loon Lakereserve, the Joseph Bighead reserve on thesouth shore of Lac des Isles and the two halvesof the Island Lake reserve (Fig. 1) were offereda therapeutic course of one of two drugs, eitheriodochlorhydroxyquin-phanquone (Mexaform) *
at the adult dosage of 2 tablets three times daily,or diloxanide furoate (Furamide), 0.5 g. threetimes daily, each to be administered for 10 days.Diloxanide furoate was used on the largersection of the Island Lake reserve and theJoseph Bighead reserve, while iodochlorhydroxy-quin-phanquone was used on the smaller part ofthe Island Lake and the Loon Lake reserves. Onall of the reserves the children who weighed lessthan 40 pounds were treated with a singleheavy dose of paromomycin sulfate (Humatin),in accordance with the recommendation ofHugonot et al.3 This drug was given in one doseof 1 c.c. of Humatin syrup per pound bodyweight (approximately 1 g. paromomycin sul¬fate per 40 pounds). Children weighing over 40pounds were given reduced dosages of the adulttherapy on a dose/weight basis.On each reserve, intensive education.four
successive days of talks, films, demonstrationsand house-to-house visits.was used to convincethe population of the necessity of complete co-
operation if this program was to have anychance of success. Substantial acceptance ofthese efforts was evident but, as expected, byless than 100% of the population. Because ofsubsequent findings it was evident that the useof paromomycin sulfate was a mistake. Evenafter the usual continuous dosage for five ormore days, we found it virtually ineffective inclearing amebic infections. In the "one-shot"dosage it probably did little but give some ofthe recipients more diarrhea. Both the iodo-chlorhydroxyquin-phanquone (Mexaform) andthe diloxanide furoate (Furamide) seemed tobe reasonably effective in clearing non-dysen-teric infections, and in a controlled study carriedout in the Onion Lake residential school, about80% clearance was achieved in asymptomaticcarriers of E. histolytica.4 The efficacy of diloxa¬nide furoate used alone in ulcerative amebicdisease has been shown by other workers5, 6 tobe less than in carriers. These findings havebeen borne out by our own experience. It isprobable therefore that in addition to the paro¬momycin sulfate-treated group, foci of infectionalso survived the mass treatment campaign inthose individuals who had ulcerative disease atthe time, even though this might have been in-sufficient to bring them for treatment.
In April 1965, the second effort at mass treat¬ment was centred on the Onion Lake reserve
(population approximately 1000), where itseemed there might be some likelihood of thedisease gaining a foothold at that time. On thisoccasion diloxanide furoate in the same dosageas before was the only drug used, except thatfor young children paromomycin sulfate syrup
was used as previously because its ineffectivenesshad not yet become evident from the previ¬ous experience.The net result of these short-term treatment
programs was to stop the apparent develop¬ment of amebic dysentery for about threemonths, after which new cases started to appear.
In the winter of 1966-67 a different approachwas used in a second attempt to achieve eradica-tion in the Loon Lake-Island Lake area fromwhich the majority of cases with this diagnosishad been coming.
In April 1966 Sivasankran et al.7 reported re¬
sults of a prolonged prophylactic trial of diloxa¬nide furoate 0.5 g. daily, compared with a com¬
pound tablet consisting of diloxanide furoate,streptomycin sulfate and chloroquine phosphate,and also with a placebo tablet, in an institu-tionalized group in Delhi. With no other meas¬
ures to prevent reinfection in a situation wherethe danger was high, these workers administereda single daily dose of one of the above to threeroughly equivalent groups totalling 186 per¬sons. The therapy was continued forfour months. The incidence of infection withE. histolytica in the group given diloxanidefuroate fell from 17 to 0%, and in the "com-pound-tablet" group from 19.6 to 1.8%. In theplacebo group the observed incidence inereasedfrom 20 to 32%.Based on this report, and from the knowl¬
edge that we had acquired of the very lowtoxicity of diloxanide furoate, it was decided toattempt continuous therapy of all the people ineach reserve for a three-month period, from theend of November to the beginning of March.Our reasons for the selection of the wintermonths for this attempt were identical with thosefor the previous effort and included: (1) theabsence of flies at this time; (2) the relativestability of the reserve populations, since thereis little trapping and almost all of the popula¬tion spend the winter at home; (3) the freezingof the lakes eliminates the use of marginalwaters for drinking purposes and reduces thelikelihood of water-borne infection at this time,and (4) the prolonged freezing conditionsseemed likely to achieve at least some
sterilization of ground surface contaminationand make possible a fresh start in the spring,with reasonable freedom from fly-borne con¬
tamination.Although in our previous efforts tablets had
been issued to each family on a daily basis, inan attempt to achieve as close supervision as
possible, this was patently impossible for sucha prolonged period. Instead, each family was
N.B. = Figures include six readmissions not included in age-sex incidence table.D indicates a death during the month.
16 12 116
for two weeks. School children in all programswere given their medication in school by theclassroom teacher. Therapy at the week-endwas the family's responsibility.As before, the results obtained showed a
decline in cases of clinical amebic disease, whichlasted for as long as this medication was con¬tinued. As a follow-up on this treatment pro¬gram a stool survey was repeated in the summer
of 1967. An incidence rate of infection with E.histolytica of 12% was found, compared with32% in the summer of 1964 before any controlmeasures had been instituted.The reduction in incidence appeared to be
maintained until the end of the summer, whenafter the usual summer rounds of sun dancesand the intermingling of families that occurs
inevitably each year an increase again becameevident in the Loon Lake area; these two eventsappear to be related. Because the author left thearea, figures do not refer to events after June1967.A study of hospital admissions (Table I) ap¬
pears to belie the statement about a decreasein incidence during the period of medication.However, during this period admissions were ofthose patients from reserves other than thetwo under treatment; no cases showed up ineither the Loon Lake or the Island Lake reserve
during the treatment period.From September 1964 to July 1967 a close
watch was kept on family contacts and on thefamily relationships of patients with a diagnosisof amebiasis. Unfortunately, the family networkin this particular group of people is so intricatelywoven, and so labile, that any attempt to recordrelationships to show interfamily spread of dis¬ease seems well-nigh impossible. However,working as closely to the families as we didwe could not help but be impressed by themanner in which the disease would appear inone member and during the course of the nextfew months affected others in the family one
after another. This observation was made earlyin the life of the project and, as it became clearthat person-to-person spread within the familywas an important.probably the most important.factor, a continuing program of family pro¬phylaxis was instituted. On the appearance ofan index case, the nurse promptly visited thefamily, utilizing the opportunity to teach basichygiene. At the same time every member of thehousehold was given diloxanide furoate in thera¬peutic doses.0.5 g. three times daily for 10days. By this time the futility of the use of paro¬momycin sulfate had been appreciated andchildren were given a suspension of diloxanidefuroate at a pro rata dosage based on weight.Later on this scheme was also abandoned as itwas found that the diloxanide furoate tablet wasso inoffensive to the taste that even very smallchildren had no objection to being given thedrug in tablet or part-tablet form (i.e., one-halfor one-quarter tablet, ete.). Such family prophy¬laxis was started in November 1965. Drug toxi-city has not been a problem. In fact the onlycomplaint of toxicity received that could reallybe traced to the drug was a report of dyspepsiain an elderly woman who forgot to take her tab¬lets for nearly two days and then tried to rectifymatters by taking five of them at one time.Over 1500 persons were given drugs (onan outpatient basis) for one or more periods oftreatment varying from 10 days to 3 months;the lack of toxicity is impressive.
DiscussionIt is not possible to say with accuracy what
has been the true incidence of amebic diseaseduring the period under consideration. Werewe to rely upon the reported incidence, our
figures would be false because of under-report-ing at times when the knowledge of the diseasewas lacking or patient and/or medical interestwas minimal, and because of considerable over-
A concerted effort was made to ascertain theminimum figures for the period 1959-67 by thesimple but time-consuming technique of check-ing every admission record to every hospital inthe area, then selecting those in which the diag¬nosis of amebiasis was a possibility and study-ing carefully the case notes of these. From suchan exercise the figures utilized in preparing theincidence chart and the age/sex incidence table(Table II) were obtained. For a diagnosis to be
TABLE II..Cases and Deaths, by Age and Sex, from AmebicColitis and Liver Abscess Admitted to Saskatchewan Hospitals
Total. 33 70 8 435Total number of patients = 110.*lndicates double diagnosis of colitis and liver abscess.
included in these statisties there had to be une-
quivocal evidence, obtained by one qualified tojudge, of true dysentery caused by E. histolytica.Amebic disease of the liver was identified byradiographie and/or liver scan evidence of pusin the liver, confirmed by aspiration biopsy or
by operation (where performed), and the thera¬peutic response to emetine hydrochloride and/orchloroquine diphosphate (Aralen*).Based on these unrefined criteria, which of
necessity excluded many patients whose diseasewas probably amebic in origin and who showedsatisfactory response to antiamebic therapy, we
considered that 110 cases of amebic diseaseoriginated in a population of approximately1000 in a nine-year period (1959-1967) (includ¬ing Bighead, Island Lake, Loon Lake and theeastern portions of Onion Lake reserves). Re-lapses and multiple admissions have in all cases
been reduced to a single digit represenring theindividual and not the individual incidence ofillness.The findings are most interesting. Although
nobody pretends there are many hard-and-fastrules about age and sex incidence, it is remark-able that in this series dysenteric disease infemales exceeded that found in males by a
ratio of 2:1. Faust's figures8 quoted from col¬lected studies for acute amebic colitis give a
ratio of 4:1 to 5:1 in favour of the male. In our
?Winthrop Chemical.
series amebic liver infection had a ratio of 2:1in favour of the male, as compared to the usuallyaccepted ratio of 7:1 in favour of the male. Theage incidence in our series is in accord withWilmot's9 statement that the maximum incidencein adults occurs in the third, fourth and fifth de-cades.The occurrence of 49 of 103 cases of amebic
dysentery in children below the age of 10 inour series is noteworthy but not unique. In1965 Nnochiri10 reported a series from the Yabaclinic in Nigeria in which 62% of all patientssuffering from acute amebic dysentery were
children under 10, and 75% of these were under5 years of age.The higher incidence rate observed in females
between the ages of 20 and 49 years may beexplained by their greater involvement withsmall children, among whom the bulk of caseshave been found. This would agree with similarfindings by the author in an outbreak of in¬fectious hepatitis in the Kenora district, where a
much higher incidence among females of child-bearing age was noticeably associated with a
high childhood incidence.11 However, Nnochiri10in his amebiasis survey in Nigeria found that96 of 102 asymptomatic mothers of infectedchildren were excreting cysts, and concludedthat the children had acquired their infectionfrom the mothers. Whichever theory is correct,there is no doubt that contact between mothersand small children is very close and spread ofenteric disease from one to the other must becommonplace.
It is less easy to explain why the male/femaleratio is so low in comparison with previouslypublished figures. If, in fact, the disease is a
newcomer in Saskatchewan, then it is possiblethat primary spread has been among the chil¬dren, the adults becoming infected second-arily. In this case a preponderance of infectedfemales might be expected from greater ex¬
posure for the reasons suggested above.The deaths, as might be expected, mainly
occurred at the extremes of life. Both the youngchildren who died were in their second year. Inone, colonic disease was non-existent and deathwas due to an abscess of the left lobe of theliver with extension to the left pleura and peri-toneum. The other died of a perforating pan-colitis, the amebic etiology of which was notconsidered until review of the pathological ma¬
terial seven years later.Among adults, perforation was the
primary cause of death, though one woman inthe seventh decade suffered a cardiac arrestwhich it was believed was possibly connectedwith the use of emetine hydrochloride. In
several of the fatal cases late diagnosis appearedto be a contributory factor, the patients havingbeen treated symptomatically for non-specific.1iarrhea or colitis until the onset of signs ofperforation prompted referral to the UniversityHospital in Saskatoon.
CONcLUSIONS
The existence of amebic disease in this area isbeyond doubt. The mode of spread appears tobe by the direct fecal-oral route, and also byffies which act as carriers.The organism is virulent, causing disease in a
relatively large proportion of those infected. Thetotal death rate has been high when expressedas a proportion of the total population; whenexpressed as a proportion of those with clini-cal disease, the rate has been less alarming. Thedisease responds favourably and quickly iftreated promptly and adequately.The question of the origin of the present out-
break is a matter for speculation. Four possi-bilities seem worthy of consideration:
1. The disease was brought into the area by avisitor.
2. The organism was aquired elsewhere by alocal inhabitant, possibly on active service, orby contact with infected individuals in migrantlabour camps. (Band members served in Korea;large members of the Indian population travelannually to the Alberta beet fields where contactwith migrant labour from the south is possible).
3. The organism is an indigenous commensalstrain which has acquired increased virulence byrapid passage in an insanitary environment.
4. The disease has been present but unrecog-nized for many years. This seems improbable.
Over the past 10 years amebic dysen-Summaru tery or hepatic abscess due to Enta-
moeba histolytica has affected 110 patients froman area of northwestern Saskatchewan immediatelyadjacent to the Alberta border and south of Lacdes Isles to the extent that they have requiredhospitalization; eight of these have died. The ma-jority of the patients have been Indians and thespread of the disease is considered to be directly
attributable to the social conditions and standardsof sanitation under which they have lived. Yet otherbands have similar standards of hygiene and sanita-tion, and have amebic infestation but no detectabledisease. Rarely has such a high case incidence ratein an affected population been reported, and seldomhas such a high incidence of children been affected.The disease appears to have been of exceptionalseverity, and to date shows little signs of abatementdespite the control measures taken by responsiblehealth service departments and associated agencies.
R4FJU1IU. Durant les 10 derni.res ann6es, ladysenterie amibienne ou des abc.s
h6patiques caus6s par Entamoeba histolytica ontfrapp6 110 malades dans une r6gion du nord-ouestde la Saskatchewan imm6diatement voisine de Iafronti.re albertaine et du sud du Lac des lies. Cesmalades ont 6t6 assez gravement atteints pour devoir.tre hospitalis.s. Huit de ces malades sont d6ced6s.La majorit6 des malades 6tait des Indiens. On croit-que Ia propagation de la maladie est directement at-tribuable . leur mode de vie, ainsi qu'aux conditionssociales et au manque d'hygi.ne qui y pr6valaient.Cependant, il y a d'autres groupes vivant sous desconditions comparables, mais chez qui on n'a paspu d6celer des maladies amibiennes m.me pal-mides personnes infect6es par E. histolytica. Rare-ment a-t'on signal6 une 6pid6mie d'une tellevirulence dans une population donn6e et on n'aque rarement vu un si grand nombre d'enfants parmiles victimes. La maladie, d'une gravit6 exception-nelle, montre jusqu'ici peu de signes de r6mission,malgr6 les mesures tr.is strictes prises par les servicesd'hygi.ne des minist.res et des organismes connexes.
REFERENCES
1. EATON, R. D. P.: Caned. J. Public Health, 56: 483,1965.
2. MEEROVITCH, E. AND EATON, R. D. P.: Amer. J. Trop.Med. Hyg., 14: 719. 1965.
3. HUGONOT, R. et at.: Bull. Soc. Med. H6p. Paris, 77:211, 1961.
4. EATON, R. D. P. AND GUZAK, P.: Med. Serv. J.Canada, 21: 815, 1965.
5. DUBEY, M. P., GUPTA. P. 5. AND CHUTTANI, H. K.:,T. Trop. Med. Hyg., 68: 63. 1965.
