Jungle yellow fever in Surinam

861 ;I'RANSACTIONS OF TIlE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE. Vol. 40. No. 6, July, 1947.

J U N G L E YELLOW FEVER IN SURINAM. BY

SNIJDERS, M. F. POLAK

E. P.

AND

J. HOEKSTRA, From the Institute for Tropical Hygiene, Royal Indian Institute, Amsterdam.

After the publication of the report by SCHOFVNER, WALCH-SORGDRAGEB and HOEKSTRA (1938, 1938a) concerning the occurrence of yellow fever in Surinam, the experiments with sera from Surinam were continued at the Institute for Tropical Hygiene at Amsterdam with the intention of testing and adding to the data published in the above-mentioned papers. SCHIJFFNER and his collaborators had reached the conclusion, that amongst the inhabitants of the Surinam primeval forest (Bush-Negroes and aboriginal Indians) that form of yellow fever prevails which is independent of the domestic mosquito A~des aegypti and which is known as jungle yellow fever because it is always found in or near the jungle (SOPER, 1936). This jungle yellow fever, as is proved by the results of serological and pathological investigations, u:~ually appears as a disease in adult men, working in the forest or in clearings, whilst the danger of infection is shown to be small for the women arid children who

862

JONGLE YELLOW FEVER

usually remain at home. Only when the house is situated in or very near the jungle is the danger of infection the same for all members of the family. It is therefore accepted that the virus of yellow fever, existing in the South American, and probably also in the African, jungle is independent of A~des aegypti (which is not found in the jungle) and of human beings who seldom visit it. The most probable hypothesis, that other vertebrates and arthropods maintain the virus cycle in the canopy of the primeval forest has been proved correct by the splendid research work of the American investigators during the great war. YELLOW FEVER IN THE SURINAM HINTERLAND.

It is shown by the results of the investigations published in 1938, that after the last known epidemic of 1908-09 at Paramaribo (FLU, 1910), yellow fever must have prevailed in Surinam. Amongst the Bush-Negroes and aboriginal Indians born after that epidemic, the mouse protection test not infrequently revealed a humoral immunity. It appeared that immunity amongst the male Bush Negroes was more frequent than amongst the Bush-Negresses (26 per cent. and 4 per cent. respectively). As the virus in these very thinly populated territories seems to exist quite independently of the presence of human beings, wc must take it for granted that here we are dealing with jungle yellow fever. At our Institute immunity is proved by the intraperitoneal mouse protection test according to SAWYER and LLOYD (1931) and by the intracerebral mouse protection test according to T~IEILER (1931), modified by DINOER (1931). The last-mentioned test is a little less sensitive but requires less serum. With both, the test animals are injected with a mixture of living virus and the serum to be examined. The presence of immune bodies in the serum as a result of an infection by yellow fever virus in the past, is proved by the fact that the mice remain alive. Results of tests may be : positive (the donor is immune); negative, inconclusive ; and, finally, unsatisfactory in ease of early death of test animals (ScHOFFNER, I939). In most cases the total number of sera obtained from one village was far too small to give an insight into the distribution according to sex and age. Therefore we combine the data of all Bush-Negroes and those of all aboriginal Indians (who live quite apart from the Bush-Negroes in the jungle). A dis. crimination between these two groups may for this reason be justified. The results of the tests on sera of 126 Bush-Negroes are here recorded, including the data published by SCHOFFNER et al. concerning tests on sera of sixty Bush-Negroes of Gansee on the Surinam river. To these are added the results of tests on three sera of Kaaimanston on the Coppenam river, ten of Maho, twelve of Makkakrcki, twenty.-eight o f Jacob-kondr6, ten of Umankondr~, and o~e of Granman-kondr6, all villages ol~. the Saramacca rive~ Another two sera come from inhabitants of the Surinam river basin,

E. P . S N I J D E I I S , M. F. POLAK AND P . HOEKS'I'RA

863

The results of the serum tests of 126 Bush-Negroes are given in "Fable I, classified according to sex and age. It shows that amongst seventy-eight men examined, twenty were found immune (26 per cent., probable error 3"3 per cent.) and amongst forty-eight women only two (4 J: 1"9 per cent.). Probably the villages of the Bush-Negroes, where the women continually stay, are not contaminated by the virus and the men are infected during their stay in the more distant forest where they carry on their work of cutting trees and managing the freight on the rivers, etc. This concurs with the phenomenon that danger of infection only arises on reaching adult age. It remains remarkable, however, that the Bush-Negress so seldom seems to come in contact with the virus. Although she keeps to her home, the villages are situated in the middle of the forest, and the impression we received from the TABLE I. AGE ANt) SEX DISTRIBUTION OF IMMUNITY TO YELLOW FEVER OF BUSH-NEGROES.

Age -group

...

1-5

6-10

2 0 0

9 0 0

(0)

(o)

g~1.--MeTl. Tested sera ... Result inconclusive Result positive .., Percentage positive

+:-I,,.-:o_3o:,,_3++!_io+

I -15 16-20 21-25

L3 0 2 [5

I0

I

l 0 (0)

3 17

10 42

2 4 40

13 0

6 2

12 0

2 0

1

0

8

(0)

1 8

0 (0)

0 1 (tOO)

Total.

78 9 20 26 -4- 3.3

B.--Women. Tested sera ... Result inconclusive Result positive ... Percentage positive

4 0 0

(o)

I 0 0 0

48 2 2 ¢ 4- l.,q

literature is that under similar circumstances ia Brazil the danger of infection is not tess for the woman than for the man. Perhaps the virus is localized in areas of the jungle which the Bush-Negress rarely visits or it is carried by a vector which bites during the night; the woman, remaining in the house, might thus be protected. Another remarkable phenomenon is that A(des aegypti--+-which, aceordi~g to BONNE and BONNE.-WEPSTER (1925), prevaii~ ~.n jungle villages such as Gansee---did not spread the virus to the women and children who remained at home. The virus could easily have been imporzcd by a marl infected elsewhere. As to the aborigirml Indians, we have the results of tests of fifty-night sera, sixteen of which are from Langaman-kondrd on tile Marowijne river, and already mentioned by SCH/3Vt~N~Ret aL Of the remaining forty-two, five are from inhabitants of Doaderkreek, four from Corneiis-kondr~. (both on the

864

JUNGLE

YELLOW

!¢/RVEIR

Wayombo river), four from Kalebaskreek on tile Coppenam, five from the Tibiti savannah (Coppenam) and twenty-four from Casipora (Surinam river). The results, classified according to age and sex, are given in Table II. Out of the forty-two men examined, twelve show a positive serum (2,9 ~: 4.7 per cent.) and four women out of sixteen (25 :k 7.0 per cent.). It is to be regretted that the material available is rather small, but our data give no indication of a smaller chance of infection for women. SNFATH(1939) found in British Guiana, amongst 246 male inhabitants of the jungle, 118 immune persons (47-9 per cent.), amongst forty-three female, eight (18-6 per cent.). He does not tell us, however, how the 174 aboriginal Indians, with sixty-eight immunes (39 per cent.) amongst them, are divided according to sex. In any case our information does not show that the Indian woman is relatively protected against yellow fever virus. This is understandable to some extent if we remember that a family of aboriginal Indians leads a nomadic life. Although it is difficult to TABLE II. AGE AND SEX DISTRIBUTION OF IMMUNITY TO YELLOW FEVER OF ABORIGINAL INDIANS. ,,i, t

i.i

Total.

Men. Total.

Women. Total.

58 4 16 28

42 3 12 29 ::k 4.7

16 1 4 25 rJ= 7"0

I Age-group

...

Men and Women. Tested sera Result inconclusive Result positive ... Percentage positive

6-15

16 - 2 5

16 2 3 19

20

9

1

1

0

O 30

2 (22)

3 30

~~

36-45 46-55

i

10

3 0 2 (67)

prove, it is very probable that the kind of yellow fever which prevails amongst Indians is jungle yellow fever. We would certainly expect higher immunity values with infection by A#des aegypti. It is worth while considering whether the epidemics that have prevailed in the capital, Paramaribo, in 1902 and 1908-09 have also penetrated the jungle. SCn0FFNER et al. already thought this could be denied and our data confirm this. Of twenty-six Bush.-Negroes and aboriginal Indians, living in the forest during the epidemics in the capital, nine were immune (38 =k 9.2 per cent.). Of sixty-one former inhabitants of Surinam, who were living at Pararnaribo during one of the two epidemics and are now staying in the Netherlands, forty (66 ±6"1 per cent.) were immune. Immunity proved here to be nearly equally divided between men (twenty-six of thirty-nine or 67 per cent.) and women (fourteen of twenty-two or 64 per cent.). Immunity rates differ considerably (31 H 1!.1 per cent.) when we compare inhabitants of the town with those of the jungle, This fact renders it improbable tha~

E. P. SNI,IDERS, M. F. POLAK AND P. HOEKSTRA

865

penetration of the primeval forests by the known epidemics has occurred, the more so because the percentage of 35 concurs with the data of the jungle infection as shown in "Fables I and II. YELLOW FEVF.R IN THE CAPITAL AND IN TIIE " DISTRICTS." So much for the inhabitants of the forest, who evidently continually run the risk of being infected. Is this also the case with the coastal population, i.e., the inhabitants of Paramaribo and those who live in the "Districts," the agricultural region near the coast ? It is mentioned in the report of 1938, that twenty-three out of 178 sera (13 per cent.), received from Surinam between 1935 and 1937, were positive. These sera came from inhabitants of Paramaribo and "districts," who were not living there during the known epidemics. It seems difficult to accept the supposition that danger of infection with the yellow fever virus existed after 1909 in the capital of Surinam or in its close vicinity. If this had been the case, the presence of many sensitive persons and the numerous A~des aegypti ought to have caused an epidemic. Such has not been observed since 1909 and it seems most unlikely that an epidemic could have occurred without being recognized. It is much more probable that the danger of infection exists in the " districts," but then the question arises of the more exact localization of the virus. The data of 1938 made it necessary in the future to distinguish between persons who were practically always living in the capital and those who lived in the " districts." We are now able to report on the tests of the sera belonging to the first-named category. In 1939, through the good offices of Dr. TILLEMA and Dr. WOLFF (who also procured many other sera from Surinam), our Institute received the sera of a number of school-children from Paramaribo. Although the schools are situated in the town, most of the children have their homes in the country. Most of them are children of British Indians, small farmers in the neighbourhood. Of ninety tested sera, none were found to have protecting properties against yellow fever virus. We also have data of thirty-six former inhabitants of Surinam, now living in the Netherlands, who were not at Paramaribo during the known epidemics. They all lived in the capital for the greater part of their stay, several of them visited the hinterland and some served at a certain time of their life on sea-going ships of the Merchant Navy. It would not have surprised us, therefore, if one of the sera should have been found to be positive. As this was not the case, we believe that we may use the results of the tests of all these thirty-six sera for judging the danger of infection, which might have existed at Paramaribo since 1909. After comparing the results obtained before and after 1938 ('Fable i~-I]).~ we think we may conclude that there is no reason to suppose that epidemics of yellow fever have occurred at or very near Paramaribo after 1909. It is, however', very probable that the " districts " have been infected. We have no reason to

866

JUN(ILE YELLOW Ir~VER

suppose that the agricultural population along the coast ran the risk of infection,, only by visiting the interior. This, in our opinion, would not happen with~ sufficient frequency to explain an immunity rate of more than 10 per cent. w e therefore conclude that yellow fever remained smouldering in the coastal regions also after 1909. The question remains whether jungle yellow fever is here playing its part or whether the virus has exclusively maintained itself' thanks to the cycle man-aegypti-man. On the plantations along the coast A~des aegypti is *ery often observed. This mosquito will certainly, if the virus. is present, be able to cause epidemics, which have, however, never been observed, though the possibility of their having occurred must still be considered. It does not, however, seem probable that man and aegypti together could form the reservoir of the virus in the " districts." Infection there is probably endemic ;: only very special circumstances in Brazil created the possibility of endemic existence of rural yellow fever, carried by A~des aegypti (SOPER, 1938). TABLE l I I. IMMUNITY TO YELLOW FEVER OF INI-IABITAN1~ OF THE COASTAL REGIONS, NOT LIVING IN THE CAPITAL DURING THE EPIDEMICS.

N u m b e r of sera e x a m i n e d ,, positive sera P e r c e n t a g e positive sera

Inhabitants of Paramaribo and districts (research 1935-37).

I n h a b i t a n t s of P a r a m a r i b o a nd close v i c i n i t y (research after 1938).

178 23 13

126 0 0

It is also possible that inhabitants of the " districts " are occasionally infected by yellow fever virus which as a rule has other hosts and, in accordance with experience gained elsewhere, probably comes from the forest. A great part of the coastal region is also covered by forest, and many plantations immediately adjoin it. The occurrence of jungle yellow fever in the coastal region is thus quite possible. We cannot, however, prove this as data are wanting as regards the places in which those we regard as immune have been infected. It is improbable that the whole coastal region could be one large focus o~ jungle yellow fever. It can more easily be accepted that the danger of the occurrence of thi,; disease is local. The surest way of localizing these supposed foci of' infection would be by the introduction of systematic viscerotomy in Surinam, as has already been done in South American countries. Viscerotomy is e:npioyed as a routine postmortem measure for the removal of liver tissue for histological examination from all persons who die within I0 days of the onset of their fatai illness. The object of organized viscerotomy is to obtain information regarding

E. P . S N I J D F . R S , M. F. P O L A K ANt) 1'. |tOI,;KSTRA

867

the presence or abser.ce of yellow fever in a definite region. In Brazil the .application of systematic compulsory viscerotomy has considerably promoted 'the yellow fever research (SOPER, RICKARD and CRAWFORD, 1934; RmKARD, 1937). The problem wc met among the inhabitants of primeval forests was, that there was no sign of the jungle yellow fever virus penetrating the Bush-Negro .and Indian villages. Neither do we see any signs of infection of the coastal regiol~s by .4~des aegypti, although this mosquito is abundant on the plantations and in the town and villages. In other words : no epidemics of yellow fever occur on the coast although sensitive persons and the vector are present and the virus is not far away. Although jungle virus can penetrate a town (WALCOTT, CRUZ, PAOLIELLO and SERAFIM, 1937), this happens less often than one would expect ; and this has also been the experience elsewhere. We cannot yet give .a definite explanation of this phenomenon. CONCLUSIONS. Serological research continued after 1938 shows that we must distinguish three regions in dealing with the yellow fever problem in Surinam (POLAK, 1944). A. The hinterland covered with primeval forest, inhabited by Bush-. Negroes and Indians. Here yellow fever prevails in its jungle form. Human infection is relatively frequent, though Bush-Negresscs rarely seem to come .in contact with the virus. B. The agricultural regions on the coast with plantations situated near the forest. Here also human infection seems fairly common. The yellow fever we meet is probably mostly jungle yellow fever. C. The capital, Paramaribo, is in close contact with the agricultural region and is yearly visited by many inhabitants of the jungle. There are no indications that yellow fever has prevailed here after 1909, but the penetration of the virus is certainly possible and the appearance of a severe epidemic would then be expected. Control of A~des aegypti and preparation of mass vacciration are very desirable. REFERENCES.

BONNE,C. • BONNE-WEPSTER,J. (1925). Mosquitoes of Surinam, p. 380. Amsterdam :

Koloniaal Instituut. DINCEn, J.E. (1931). Gelbficber bei weizen M/iusen. Cent. Bact. 1. Abt. Orig., 121,154. FLU, P. C. (1910). Beobaehtungen wahrend der Gelfieberepidemie die von Dezember 1908 bis Februar 1909 in Paramaribo herrschte. Z. Hyg. Infekt. Kr., 65, 17. POLAK,M.F. (1944). Vraagstukken der Gele Koorts ; Epidemiologie en Vaccinatie. Thesis, Amsterdam, 1945. RICKAaD, E. R. (1937). The organisation of the viscerotome service of the Br~ili~m co-operative yellow fever service. Amer, y. trop. ~Vled., 17, 163. SAw'~m, W. A. & LLOYD, W. (1931). The use of mice in tests of immunity against yeUow fever. J. exp. Nled., 54, 533.

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JUNGLE. YELLOW FI~VER

ScvIOFFNma, W.

(1939).

Yellow fever--some remarks on Dr. Soper's paper.

Trans. R.

Soc. trop. Med. Hyg., 32, 587. , VCALCrI-SoRGDRAr~ER,B. & HOEKSTaA, J. (1938). Laatste resultaten van het onder-. zoek naar bet voorkomen van gele koorts in Suriname. Geneesk. 7ijdschr. Ned.-Ind.,

78,571. , & . (1938a). Sur la persistance de la fi~vrejaune en Guyane hollandaise, d~montrg par le test de protection de la souris. Bull. Office Internat. Hyg. Pub., 30, 1228. SNEATH, P. A . T . (1939). Yellow fever in British Guiana. Trans. R• Soc. trop. M e d Hyg., 33, 241. SOPER, F . L . (1936). Recent extensions of knowledge of yellow fever. Quart. Bull. Hlth. Org. L.o.N., 5, 19. • (1938). Yellow fever: the present situation (October, 1938) with special reference to South America. Trans..R. Soc. trop. Med. Hyg., 82, 297. , RlCKARD, E. R. & C~WFORD, P . J . (1934). T h e routine post-mortem removal of liver tissue from rapidly fatal fever cases for the discovery of silent yellow fever loci. Amer. ft. Hyg., 19, 549. TH~.IL~.R, M. (1931). Neutralisation tests with immune yellow fever sera and a strain of yellow fever virus adapted to mice. Ann. trop. Med. Parasit., 25, 69. WALCOTr, A. M., CRUZ, E., P^OLIELLO, A. & SEn^FIM, J. (1937). An epidemic of urban yellow fever which originated from a ease contracted in the jungle. Amer. ft. trop. Med., 17, 677•