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Comparative susceptibility to Schistosoma mansoni of the squirrel monkey, the slow loris and the tree shrew
534 TRANSACTIONSOF THE ROYAL SOCIETYOF TROPICAL MEDICINE AND HYGIENE. Vol. 61. No. 4. 1967.
COMPARATIVE SUSCEPTIBILITY TO SCHISTOSOMA MANSONI OF THE SQUIRREL MONKEY, THE SLOW LORIS AND THE TREE SHREW BY
K E N N E T H S. WARREN AND
JOHN A. JANE
Departments of Preventive Medicine, Medicine and Neurosurgery, Western Reserve University School of Medicine, Cleveland, Ohio Introduction Until recently all primate species tested in the laboratory have been susceptible to infection with Schistosoma mansoni. These included only members of the Anthropoidea represented by Old World or higher New World monkeys (MARTINS, 1958). In the past year, however, the marmoset (Callithrix jacchus and C. penicilata), most primitive of the New World monkeys, was reported to be relatively resistant to S. mansoni infection (WARRENand SIM-ES, 1966). This observation prompted the present investigation in which the susceptibilities of 1 Anthropoid and 2 Prosimian species were compared. The squirrel monkey (Saimiri sciurea), never before exposed to S. mansoni in the laboratory, was chosen as the representative of the Anthropoidea. The lower species (suborder Prosimii) were represented by the slow loris (Nycticebus coucang) and the Malayan tree shrew (Tupaia glis). The latter's exact taxonomic status is controversial, but it can be considered to be either the lowest of the extant primates or an advanced "pre-primate" (SIMPSON, 1965). Both species of lower primates were much less susceptible to infection with S. mansoni than the higher primate species.
Materials and methods The animals were exposed to counted numbers of cercariae obtained from a pool of 25 dustralorbis glabratus infected with a Puerto Rican strain of S. mansoni by either placing the cercariae on the shaved abdomen of pentobarbital anaesthetized animals (C) or injecting the cercariae subcutaneously in unanaesthetized animals (SC) (Table I). 8 weeks after exposure the animals were anaesthetized and the portal and mesenteric venous systems were perfused in order to obtain and count the adult worms (RADKE et al., 1961). As control animals of known susceptibility to S. mansoni., 18 Swiss This investigation was conducted under the sponsorship of the Commission on Parasitic Diseases of the Armed Forces Epidemiological Board, and was supported in part by the Office of The Surgeon General, Department of the Army. Support was also provided by National Institutes of Health grant NB--00779 and Cleveland Veterans Administration Hospital, grant CH--1-66.
KENNETH S. WARREN AND J O H N A. JANE
535
albino mice (SC) and 9 rhesus monkeys (Macaca mulatta) (4 C, 5 SC) were exposed simultaneously with those above. The mice, which had been exposed to 177 cercariae each, were perfused at 8 weeks. The rhesus monkeys, which were exposed to 500 to 2000 cercariae, were not perfused at 8 weeks as they were to be used for other experiments, but their stools and liver biopsies were examined for the presence of schistosome eggs. Results All 18 of the Swiss albino mice and all 9 of the rhesus monkeys were infected with S. mansoni, as were all 6 of the squirrel monkeys. In contrast, 5 of the 7 lorises and only 3 of the 7 tree shrews were infected after exposure to large numbers of cercariae. In the mice 27"0% (range 5-51-5) of cercariae to which they had been exposed, developed to adult stage and in the squirrel monkeys 14" 5% (range 0.6-29.9) (Table I). In the lorises, however, only 2- 0% (range 0-4" {3) developed and in the tree shrews 0.6% (range 0-2.0) (Table I). Discussion The marked individual variation in the worm-cercaria ratio within each of the species studied (Table I) is a commonly observed phenomenon, the cause of which is now under investigation. Although there is relatively little difference in the numbers of cercariae which penetrate mice, there is great variation in the numbers of worms which subsequently develop to maturity (STmEWALTet al., 1965). There thus appears to be a marked difference in individual susceptibility to infection with S. mansoni among experimental animals. It should be noted, however, that although this individual variation occurs consistently, the average worm-to-cercaria ratio among groups of animals remains relatively constant. In a recent study of several orders of mammals, not including primates, no correlation between susceptibility to infection with S. mansoni and phyletic position could be found (Bruce et al., 1961). On the basis of the present study, however, it appears that at least in general terms there may be a correlation between primate phylogeny as repre sented by a s e ries ofextantmammals(LEGRosCLARK, 1962)andnaturalimmunitytoS. mansoni. Thesquirrel monkey was easily infected, as have been all other Anthropoidea except the lowest of this suborder, the marmoset (WARREN and SIMSES, 1966). In contrast, a member of the suborder Prosimii (Nycticebus coucang) appeared to be highly resistant to infection, and the Malayan tree shrew, whose systematic position is uncertain since it has characteristics in common with both the insectivores and the lowest of the primates (JANE et al., 1965; VAN VALEN, 1965; MCKENNA, 1966) was almost insusceptible to infection under the conditions of these experiments. It should be added that none of the animals used in the present study could have been naturally infected with S. mansoni as they all came from non-endemic areas. When the results of the present study are compared with similar experiments with other primates (WARRENand SIM~ES,1966; BRENERand ALVARENGA,1962; SADUNet al., 1964) a progressive susceptibility to S. mansoni is found in the primate order (Figure). Such a comparison among studies performed in different laboratories may be valid for the following reasons: Although the results of perfusions of our 9 rhesus monkeys could not be used in the present experiments as they were not perfused at 8 weeks but at 15 and 20 weeks after exposure to cercariae, some rhesus monkeys from the laboratory of Dr. Elvio H. Sadun, from which our Puerto Rican strain of parasite and snail had originally been obtained, were perfused at 8.5 weeks and were found to harbour approxi-
536
COMPARATIVE SUSCEPTIBILITY TO
TABLE I.
Schistosoma mansoni
Results of exposure of New World monkeys (Saimiri), prosimian primates (Nycticebus), and "pre-pftmates" (Tupaia) to Schistosoma mansoni. 8 weeks after exposure Route of infection
Number of cercariae
Number of worms
SC* SC SC SC SC SC
1,000 1,000 1,000 1,000 500 500
299 298 157 6 47
Woru'is:
• cercariae ratio (%)
Squirrel monkey ( Saimiri sciurea)
8
29 "9 29 "8 !
15 "7
0"6 9"4 1"6
14"5 Slow lofts (Nycticebus coucang) 1
2 3 4 5 6 7
SC SC SC SC SC SC C**
1,000 1,000 1,000 500 500 500 2,000
36 19 0 25 11 8
0
3"6 1"9 0"0 5-0 2.2 1-6 0"0 2.0
Malayan tree shrew ( Tupaia glis) 1
2 3 4 5 6 7
SC SC SC SC SC C C
500 500 500 500 500 500 500
10 8 4 0 0 0 0
2-0 1-6 0-8 0.0 0.0 0.0 0.0 0.6
*Subcutaneous
**Cutaneous
mately 27% worms (SADVNet al., 1964). Both the cebus monkeys and the marmosets, as shown in the Figure, were infected with a Brazilian strain of S. mansoni (WAgRnq and SrraSEs, 1966; Bm~NER and Ar.VARENGA, 1962). Within this strain there also was a marked difference in susceptibility between a higher (cebus monkey) and lower primate (marmoset). Brazilian and Puerto Rican strains of S. mansoni have been compared in mice in our laboratory in relation to the percentage of adult worms developing after the penetration of a known number of cercariae. The Brazilian strata had approximately 180% of the virulence of the Puerto Rican strain in this regard (Warren). Nevertheless, evenifthe data inthe Figure were adjusted for this factor, they would still reveal a marked difference in susceptibility between the higher and lower primates. It appears, therefore, that in comparison with the higher primates, the lower primates are relatively resistant to infection with S. mansoni.
KENNETH S. WARREN AND JOHN A. JANE
RHESUS MONKEY (Macoca mulQtto)
Y//////////////~///////////////////////////////////////////////A~
CEBUS MONKEY (Cebus opella)
"////////)'/////////////II/~///////////////////A
A pattern of susceptibility to Schistosoma mansoni among primates in relation to the percentage of worms developing after exposure to a given number of cercariae. *Present study "fWarren and Sim6es, 1966 *Brener and Alvarenga, 1962 aSadun et al., 1964
SOUIRREL MONKEY ~//////////////////////////////J/.//////A :~ (Soirniri sciurea) MARMOSET {Callithrix jacchus) LORIS (Nycticebus coucang) TREE SHREW (Tupoio glls)
WORMS
537
/ cercariae × I00
SU~V,aRY
After exposure to cercariae of Schistosoma mansoni it was found that a New World monkey (Saimiri sciurea--the squirrel monkey) was susceptible to infection, a prosimian primate (Nycticebus coucang--the slow loris) was relatively resistant, and a "pre-primate" (Tupaia glis--the tree shrew) was virtually insusceptible to infection. On the basis of this and other studies with primates, it appears that the lower primates are less Susceptible to infection with S. mansoni than the higher primates. REFERENCES BREWER, Z. & ALVARENGA,R. J. (1962). Rev. Inst. Med. trop. S. Paulo, 4, 180. BRUCE J. E., LLEWELLYN,L. M. & SADUN, E. H. (1961). J. Parasit., 47, 753. JAhrE, J. A., CAMPBELL,C. B. G., & YASHON,D. (1965). Science, 147, 153. LEGROS CLARK,W. E. (1962). The Antecedents of Man. An Introduction to the Evolution of the Primates. Edinburgh: The Edinburgh University Press. MARTINS, A. V. (1958). Bull. Wld. Hlth. Org., 18, 931. MCKENNA, M. C. (1966). Folio Primat., 4, 1. RADKE, M. G., BERRZos-DuRAN, L. A. & MORAN, K. (1961). J. Parasit., 47, 366. SADIYN,E. H.,BRUCE, J: I. & MACOMBER,P. B. (1964). Amer. J. trop. Med. Hyg., 13, 548. STIREWALT,M. A., SHEPPERSON, J. R. • LINClCO~WE,D. R. (1965). Parasitology, 55, 227. VAN VALEN, L. (1965). Evolution, 19, 137. WARREN, K . S . Trans. R. Soc. trop. Med. Hyg., (in press). & SIM6ES, J., JR. (1966). Amer. J. trop. Med. Hyg., 15, 153.
COMPARATIVE SUSCEPTIBILITY TO SCHISTOSOMA MANSONI OF THE SQUIRREL MONKEY, THE SLOW LORIS AND THE TREE SHREW BY
K E N N E T H S. WARREN AND
JOHN A. JANE
Departments of Preventive Medicine, Medicine and Neurosurgery, Western Reserve University School of Medicine, Cleveland, Ohio Introduction Until recently all primate species tested in the laboratory have been susceptible to infection with Schistosoma mansoni. These included only members of the Anthropoidea represented by Old World or higher New World monkeys (MARTINS, 1958). In the past year, however, the marmoset (Callithrix jacchus and C. penicilata), most primitive of the New World monkeys, was reported to be relatively resistant to S. mansoni infection (WARRENand SIM-ES, 1966). This observation prompted the present investigation in which the susceptibilities of 1 Anthropoid and 2 Prosimian species were compared. The squirrel monkey (Saimiri sciurea), never before exposed to S. mansoni in the laboratory, was chosen as the representative of the Anthropoidea. The lower species (suborder Prosimii) were represented by the slow loris (Nycticebus coucang) and the Malayan tree shrew (Tupaia glis). The latter's exact taxonomic status is controversial, but it can be considered to be either the lowest of the extant primates or an advanced "pre-primate" (SIMPSON, 1965). Both species of lower primates were much less susceptible to infection with S. mansoni than the higher primate species.
Materials and methods The animals were exposed to counted numbers of cercariae obtained from a pool of 25 dustralorbis glabratus infected with a Puerto Rican strain of S. mansoni by either placing the cercariae on the shaved abdomen of pentobarbital anaesthetized animals (C) or injecting the cercariae subcutaneously in unanaesthetized animals (SC) (Table I). 8 weeks after exposure the animals were anaesthetized and the portal and mesenteric venous systems were perfused in order to obtain and count the adult worms (RADKE et al., 1961). As control animals of known susceptibility to S. mansoni., 18 Swiss This investigation was conducted under the sponsorship of the Commission on Parasitic Diseases of the Armed Forces Epidemiological Board, and was supported in part by the Office of The Surgeon General, Department of the Army. Support was also provided by National Institutes of Health grant NB--00779 and Cleveland Veterans Administration Hospital, grant CH--1-66.
KENNETH S. WARREN AND J O H N A. JANE
535
albino mice (SC) and 9 rhesus monkeys (Macaca mulatta) (4 C, 5 SC) were exposed simultaneously with those above. The mice, which had been exposed to 177 cercariae each, were perfused at 8 weeks. The rhesus monkeys, which were exposed to 500 to 2000 cercariae, were not perfused at 8 weeks as they were to be used for other experiments, but their stools and liver biopsies were examined for the presence of schistosome eggs. Results All 18 of the Swiss albino mice and all 9 of the rhesus monkeys were infected with S. mansoni, as were all 6 of the squirrel monkeys. In contrast, 5 of the 7 lorises and only 3 of the 7 tree shrews were infected after exposure to large numbers of cercariae. In the mice 27"0% (range 5-51-5) of cercariae to which they had been exposed, developed to adult stage and in the squirrel monkeys 14" 5% (range 0.6-29.9) (Table I). In the lorises, however, only 2- 0% (range 0-4" {3) developed and in the tree shrews 0.6% (range 0-2.0) (Table I). Discussion The marked individual variation in the worm-cercaria ratio within each of the species studied (Table I) is a commonly observed phenomenon, the cause of which is now under investigation. Although there is relatively little difference in the numbers of cercariae which penetrate mice, there is great variation in the numbers of worms which subsequently develop to maturity (STmEWALTet al., 1965). There thus appears to be a marked difference in individual susceptibility to infection with S. mansoni among experimental animals. It should be noted, however, that although this individual variation occurs consistently, the average worm-to-cercaria ratio among groups of animals remains relatively constant. In a recent study of several orders of mammals, not including primates, no correlation between susceptibility to infection with S. mansoni and phyletic position could be found (Bruce et al., 1961). On the basis of the present study, however, it appears that at least in general terms there may be a correlation between primate phylogeny as repre sented by a s e ries ofextantmammals(LEGRosCLARK, 1962)andnaturalimmunitytoS. mansoni. Thesquirrel monkey was easily infected, as have been all other Anthropoidea except the lowest of this suborder, the marmoset (WARREN and SIMSES, 1966). In contrast, a member of the suborder Prosimii (Nycticebus coucang) appeared to be highly resistant to infection, and the Malayan tree shrew, whose systematic position is uncertain since it has characteristics in common with both the insectivores and the lowest of the primates (JANE et al., 1965; VAN VALEN, 1965; MCKENNA, 1966) was almost insusceptible to infection under the conditions of these experiments. It should be added that none of the animals used in the present study could have been naturally infected with S. mansoni as they all came from non-endemic areas. When the results of the present study are compared with similar experiments with other primates (WARRENand SIM~ES,1966; BRENERand ALVARENGA,1962; SADUNet al., 1964) a progressive susceptibility to S. mansoni is found in the primate order (Figure). Such a comparison among studies performed in different laboratories may be valid for the following reasons: Although the results of perfusions of our 9 rhesus monkeys could not be used in the present experiments as they were not perfused at 8 weeks but at 15 and 20 weeks after exposure to cercariae, some rhesus monkeys from the laboratory of Dr. Elvio H. Sadun, from which our Puerto Rican strain of parasite and snail had originally been obtained, were perfused at 8.5 weeks and were found to harbour approxi-
536
COMPARATIVE SUSCEPTIBILITY TO
TABLE I.
Schistosoma mansoni
Results of exposure of New World monkeys (Saimiri), prosimian primates (Nycticebus), and "pre-pftmates" (Tupaia) to Schistosoma mansoni. 8 weeks after exposure Route of infection
Number of cercariae
Number of worms
SC* SC SC SC SC SC
1,000 1,000 1,000 1,000 500 500
299 298 157 6 47
Woru'is:
• cercariae ratio (%)
Squirrel monkey ( Saimiri sciurea)
8
29 "9 29 "8 !
15 "7
0"6 9"4 1"6
14"5 Slow lofts (Nycticebus coucang) 1
2 3 4 5 6 7
SC SC SC SC SC SC C**
1,000 1,000 1,000 500 500 500 2,000
36 19 0 25 11 8
0
3"6 1"9 0"0 5-0 2.2 1-6 0"0 2.0
Malayan tree shrew ( Tupaia glis) 1
2 3 4 5 6 7
SC SC SC SC SC C C
500 500 500 500 500 500 500
10 8 4 0 0 0 0
2-0 1-6 0-8 0.0 0.0 0.0 0.0 0.6
*Subcutaneous
**Cutaneous
mately 27% worms (SADVNet al., 1964). Both the cebus monkeys and the marmosets, as shown in the Figure, were infected with a Brazilian strain of S. mansoni (WAgRnq and SrraSEs, 1966; Bm~NER and Ar.VARENGA, 1962). Within this strain there also was a marked difference in susceptibility between a higher (cebus monkey) and lower primate (marmoset). Brazilian and Puerto Rican strains of S. mansoni have been compared in mice in our laboratory in relation to the percentage of adult worms developing after the penetration of a known number of cercariae. The Brazilian strata had approximately 180% of the virulence of the Puerto Rican strain in this regard (Warren). Nevertheless, evenifthe data inthe Figure were adjusted for this factor, they would still reveal a marked difference in susceptibility between the higher and lower primates. It appears, therefore, that in comparison with the higher primates, the lower primates are relatively resistant to infection with S. mansoni.
KENNETH S. WARREN AND JOHN A. JANE
RHESUS MONKEY (Macoca mulQtto)
Y//////////////~///////////////////////////////////////////////A~
CEBUS MONKEY (Cebus opella)
"////////)'/////////////II/~///////////////////A
A pattern of susceptibility to Schistosoma mansoni among primates in relation to the percentage of worms developing after exposure to a given number of cercariae. *Present study "fWarren and Sim6es, 1966 *Brener and Alvarenga, 1962 aSadun et al., 1964
SOUIRREL MONKEY ~//////////////////////////////J/.//////A :~ (Soirniri sciurea) MARMOSET {Callithrix jacchus) LORIS (Nycticebus coucang) TREE SHREW (Tupoio glls)
WORMS
537
/ cercariae × I00
SU~V,aRY
After exposure to cercariae of Schistosoma mansoni it was found that a New World monkey (Saimiri sciurea--the squirrel monkey) was susceptible to infection, a prosimian primate (Nycticebus coucang--the slow loris) was relatively resistant, and a "pre-primate" (Tupaia glis--the tree shrew) was virtually insusceptible to infection. On the basis of this and other studies with primates, it appears that the lower primates are less Susceptible to infection with S. mansoni than the higher primates. REFERENCES BREWER, Z. & ALVARENGA,R. J. (1962). Rev. Inst. Med. trop. S. Paulo, 4, 180. BRUCE J. E., LLEWELLYN,L. M. & SADUN, E. H. (1961). J. Parasit., 47, 753. JAhrE, J. A., CAMPBELL,C. B. G., & YASHON,D. (1965). Science, 147, 153. LEGROS CLARK,W. E. (1962). The Antecedents of Man. An Introduction to the Evolution of the Primates. Edinburgh: The Edinburgh University Press. MARTINS, A. V. (1958). Bull. Wld. Hlth. Org., 18, 931. MCKENNA, M. C. (1966). Folio Primat., 4, 1. RADKE, M. G., BERRZos-DuRAN, L. A. & MORAN, K. (1961). J. Parasit., 47, 366. SADIYN,E. H.,BRUCE, J: I. & MACOMBER,P. B. (1964). Amer. J. trop. Med. Hyg., 13, 548. STIREWALT,M. A., SHEPPERSON, J. R. • LINClCO~WE,D. R. (1965). Parasitology, 55, 227. VAN VALEN, L. (1965). Evolution, 19, 137. WARREN, K . S . Trans. R. Soc. trop. Med. Hyg., (in press). & SIM6ES, J., JR. (1966). Amer. J. trop. Med. Hyg., 15, 153.