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Glandular toxoplasmosis
C o m m e n t s o n C u r r e n t Literature GLANDULAR TOXOPLASMOSIS LTHOUGH the protozoan parasite toxoplasma had been described A as early as 1908 in a North African
9
rodent, the gondi, and about the same time in the wild rabbit in Brazil, it was not established definitely until 1939 that the agent could produce disease in the human subject. 1 Clinical manifestations of the disease were recognized first in the form of congenital toxoplasmosis: encephalomyelitis in early infancy, usually with ehorioretinitis. Typical. manifestations of infection in the newborn infant included hepatomegaly, splenomegaly, icterus, maculopapular rash, chorioretinitis, and cerebral calcification, with the subsequent development of hydrocephalus, or microcephaly, a not uncommon result. While the congenital forms of toxoplasmosis have continued to be a striking manifestation of this infection, it has become increasingly apparent that the acquired postnatal form is common, and that the manifestations of this infectious process may vary widely: from inapparent infection to definite clinical disease, which includes meningoencephalitis, glandular involvement, or eye involvement. Clinical manifestations in some instances may simulate those of the rickettsial diseases. A practical classification of toxoplasmic infection in human subjects, suggested by Beckett and FIynn 2 in 1953, serves to emphasize the wide variety of clinical manifestation for which the toxoplasma organism may be responsible: (1) a silent infection essentially asymptomatic; (2) a mild grippe-like infection similar in some
respects to nonparalytic poliomyelitis; (3) a mild infection simulating infectious mononucleosis which is characterized by enlarged glands and slow convalescence, with eventual complete recovery, and with negative PaulBunnell test; (4) chorioretinitis; (5) an acquired systemic infection occurring in adults and children which gives rise to signs and symptoms of widespread disease. In this last category, the illness may be characterized by a rash which spares the scalp, palms of the hands, and soles of the feet, suggestive of acute rickettsial infection; by an encephalitis without visceral involvement; by chorioretinitis; or by a febrile illness suggesting widespread collagen disease. Congenital toxoplasmosis, discussed by these authors as a separate category, is divided further into two essential types with allowance for overlapping manifestations: (a) a severe febrile illness beginning in the immediate neonatal period with vomiting, convulsions, and nystagmus, followed by progressive hydrocephalus, ehorioretinitis, and cerebral calcification, which is characteristically diffuse and spotty; and (b) predominant perinatal manifestations similar to those seen in erythroblastosis fetalis : jaundice and hepatosplenomegaly. Of particular interest to the cliniciar~ is a glandular form of toxoplasmic disease, reported currently in medical literature, which contributes significantly to the etiologic diagnosis of lymphadenopathy of unknown origin. In Denmark, Slim 3 has encountered over 100 such cases, and estimates that toxoplasma infection 388
COMMENTS ON CURRENT LITERATURE
accounts for about 5 pe r cent of the cases of lymphadenopathy of unknown origin. In a recent issue of Lancet a report from the University of Sheffield appears; this report by Beverley and Beattie 9 is entitled "Glandular Toxoplasmosis : A Survey of Thirty Cases." Earlier studies by Beattie 5 which were based on antibody titers had indicated that in the areas surveyed subclinical infection with toxoplasma was relatively common. In Lincolnshire, for example, 36 per cent of the country-dwellers and 22 per cent of the town-dwellers had dye-test antibodies (Sabin-Feldman) to a titer of 1:16, or higher. In the more recent clinical studies also, Beverley and Beattie made use of the Sabin-Feldman 6 dye test for the diagnosis of active infection, following the principle that the dye-test titer should increase eight-fold, or more, at least to a level of 1:256. In the presence of active infection, the titer will be maintained at or near this level for several weeks. ~[n addition to the dye test, the authors have employed complement-fixation antibody procedures f or verification, and state that " t h e level of the complement-fixing antibody should either change from negative to positive and rise to a titre of 1/s, or, if positive initially, should subsequently increase at least four-fold. ''~ For purposes of this recent clinical study, Beverley and Beattie adopted an arbit r a r y level of 1:256 for the dye-test titer, and a complement-fixation titer of 1:10, the results obtained being correlated wherever possible with search for the toxoplasma organism. In 4 of the 30 cases described, toxoplasma organisms were isolated from excised glandular tissue by the inoculation of mice. As the authors emphasize, these organisms when obtained from man often prove of low virulence for laboratory animals. However, in some instances in which the animals are free of objective signs, toxoplasmic cysts may be seen in the brains of inoculated animals for as long as a month, or more, after inoculation. This problem of low virulence
3~9
in relation to exact etiologic diagnosis may be solved to some extent by the use of methods more recently developed: inoculation of the embryonatcd egg and of tissue culture preparations.' It is difficult also to detect the parasite in stained sections of lymph glands excised from human subjects; after long search Stanton and Pinkerton s were able to report the finding of one cyst. Likewise, the pathologic changes observed in human lymph nodes are not characteristic, being described in some instances as a "lymphohistiocytic medullary retieulosis," and in others as a "focal medullary reticulosis." In the cases of glandular toxoplasmosis reported currently, the initial clinical diagnosis most commonly considered was that of infectious mononucleosis. Other clinical impressions included tonsillitis, mumps, Hodgkin's disease, lymphosarcoma, leukemia, aleukemic leukemia, and poliomyelitis, indicating that the clinical manifestations are so varied as to be of little aid in diagnosis. None of the patients with glandular toxoplasmosm showed a positive Paul-Bunnell reaction. The age incidence is of interest: 10 of the 30 patients were under the age of 10 years, 11 patients were between the ages of 11 and 20 years, 4 patients ranged in age from 20 to 30 years, a~d 5 of the 30 patients were over 30 years of age. This age distribution is similar to the age incidence of infectiot~s mononucleosis in children and young adults. The clinical manifestations of the disease process varied greatly in severity and duration. Some were never ill; others complained that they were " be l ow p a r " for weeks. In 20 of the 30 patients, swelling and pain in the lymph glands (usually cervical) were noted initially. As a rule, these enlarged glands regressed vei:y slowly, sometimes requiring many months for return to normal size. Sore throat, which was not a prominent symptom, was noted initially in only 7 patients, but developed later in the course in 3 others. Other symptoms
390
THE
J O U R N A L OF P E D I A T R I C S
included severe headache, fatigue, depression, and muscle pain. From the clinical point of view, it is of interest that none of the 30 patients experienced high fever and 11 of them were afebrile. In some patients, pain in the neck and the back led to the suspicion of poliomyelitis, and in other instances meningismus was suspected. Several complained of pain in the joints and limbs and in some abdominal pain was present, suggesting some degree of mesenteric lymphadenitis. Fatigue was a common manifestation, and in some instances was long continued. Blood studies in 6 patients revealed an absolute leukocytosis; in 15 patients lymphocytosis was observed, and in 6, cells of the glandular-fever type were reported. In only one instance was there any suggestion of pulmonary involvement, and in one other instance enlarged hilar nodes were noted on x-ray examination. No serious sequelae were reported in this se~'ies of 30 patients. The source of infection in human toxoplasmosis is not known definitely ; animals have been suspected, since the organism is to be found in many animals and birds potentially associated with man: the gondi in Africa; mice, rats, rabbits, guinea pigs, squirrels, foxes, mink, chinchilla, dogs, cats, swine, sheep, cattle, various primates, as well as pigeons, chickens, ducks, and penguins2 The animals most commonly suspected are dogs, cats, and rabbits. In the series of patients with glandular toxoplasmosis currently reported from England, 4 21 had association with dogs, in some instances close contact; 12 with cats, and 5 with budgerigars, a psittaeine bird becoming increasingly popular as a pet. The significance of close association with animals or birds is indicated by the known occurrence of toxoplasma organisms in the droppings of birds, in the urine, feces, and saliva of animals, and also in the saliva of man. While the route of invasion in man is not known, it has been suggested that the organism may gain access to the body through the mucous membrane of the
tonsillo-pharyngeal region, since cervical adenopathy is a common manifestation. The widespread occurrence of toxoplasma infection in the human subject is reflected by surveys carried out on the human population in various parts of the world. Such a survey reported recently from the Toronto area by Harper, Ormsby, and Coekeram 1~ indicates that positive skin test for toxoplasmin increases with age from about 10 per cent positive in the youngest age group studied to 40 per cent positive in the older age group. Also, the presence of complement-fixing antibodies in normal members of the population in this area would indicate that inapparent and unrecognized toxoplasmic infections are widespread. Thus, it appears that human infection with toxoplasma organisms is more common than has been supposed heretofore. Lymphadenopathy as a clinical manifestation appears to be one of the more common forms of acquired toxoplasmosis, and it seems reasonable that the various diagnostic tests for toxoplasmosis are indicated whenever the clinician encounters an unusual form of glandular involvement in the human subject. Since inapparent infection in the pregnant woman may result in abnormalities in the fetus, diagnosis would be of particular value in this group. The treatment of toxoplasmic infections has not been entirely satisfactory; reports in the literature, however, suggest that a combination of sulfadiazine and pyrimethamine, or triple sulfonamides plus pyrlmethamine may be of value. 4, 9 Since pyrimethamine is a folie acid antagonist, and severe leukopenia may result from its use, leukocyte counts should be checked at frequent intervals in order to detect any adverse reaction to this drug. The prevalence of toxoplasma infection among animals and birds would suggest that careful scrutiny be given the possible animal sources of human toxoplasmosis, particularly household pets. The recognition of toxoplasmosis as an infection widespread in the
COMMENTS ON CURRENT LITERATURE
human population, and current emphasis on the protean manifestations of this disease, including glandular involvement, particularly in the cervical region, should alert the clinician to this diagnostic possibility whenever unusual cases of glandular fever are encountered.
4. 5.
RUSSELL J. BLATTNER REFERENCES 1. Wolf~ A., Cowen, D., a n d Paige, B. H.: H u m a n Toxoplasmosis: Occurrence in I n f a n t s as an Encephalomyelitis; Verification b y Transmission to Animals, Science 89: 226~ 1939. Toxoplasmlc Encephalomyelitis: A New Case of Granulomatous Encephalomyelitis Duo to a Protozoan, Am. J. Path. 15: 657~ 1939. Toxoplasmie Encephalomyelitis: Experimental Transmission of I n f e c t i o n to Animals F r o m a H u m a n I n f a n t , J. Exper. Med. 71: 187, 1940. Sabin, A . B . : Biologic and Immunological I d e n t i t y of Toxoplasma of Animal and H u m a n Origin, Prec. Soc. Exper. Biol. & Med. 41: 75, 1939. 2. Beckett, R. S., and F l y n n , F. J., Jr.: Toxoplasmosis: Report of Two New Cases, W i t h a Classification and W i t h a Demonstration of the Organisms in the H u m a n Placenta, New England J. Med. 249: 345, 1953. 3. Slim, J. C.: Toxoplasma Acquisita Lymphonodosa: Clinical and Pathological Aspects, Ann. New York Acad. Sc. 64: 185, 1956. Conference on Clinical
6.
7.
8.
9. 10.
391
Aspects and Diagnostic P r o b l e m s of Toxoplasmosis in Paediatrics, E i g h t h I n t e r n a t i o n a l Congress of Paediatrics, Copenhagen, Denmark, July 25 to 26, Discussion-Vol., Copenhagen, Denmark, Berlingska Boktryckeriet, 1956, p. 40]. Beverley, J-. K. A., and Beattie, C. P.: Glandular Toxoplasmosis: A S u r v e y of T h i r t y Cases~ Lancet 2: 379, 1958. Beattie, C. P.: Clinical and Epidemiological Aspects of Toxoplasmosis, Tr. Roy. Soc. Trop. Med. & Hyg. 51: 96, 1957. Sabin, A. B., and Feldman, H. A.: Dyes as Microchemical I n d i c a t o r s of a New I m m u n i t y Phenomenon Affecting a Protozoan P a r a s i t e (Toxoplasma), Science 108: 660, 1948. Chernin, E., and Weller, T. H.: Serial Propagation of Toxoplasma gondii in Roller Tube Cultures of Mouse and Human Tissues, Prec. Soc. Exper. Biol. & Med. 85: 68, 1954. F u r t h e r Observations on the G r o w t h of Toxoplasma gondii in Roller Tube Cultures of Mouse aud Primate Tissues, J. Parasitol. 43: 33, 1957. Balducci, D., and Tyrrell, D.: Quantit a t i v e Studies of Toxoplasma gondii in Culture of Trypsin-Dispersed Mammalian Cells, Brit. J. Exper. Path. 37: 168, 1956. Stanton, M. F., and Pinkerton, H.: Benign Acquired Toxoplasmosis W i t h Subsequent Pregnancy, Am. J. Clin. P a t h . 23: 1199, 1953. Feldmau, H. A.: Toxoplasmosis: Review Article, P e d i a t r i c s 22: 559, 1958. Harper, D. W., Ormsby, H. L., and Cockeram, A.: A Su'rvey of Skill and Complement F i x a t i o n Tests for Toxoplasmosis in the Toronto Area, Canad. M. A. J. 79: 25, 1958.
9
rodent, the gondi, and about the same time in the wild rabbit in Brazil, it was not established definitely until 1939 that the agent could produce disease in the human subject. 1 Clinical manifestations of the disease were recognized first in the form of congenital toxoplasmosis: encephalomyelitis in early infancy, usually with ehorioretinitis. Typical. manifestations of infection in the newborn infant included hepatomegaly, splenomegaly, icterus, maculopapular rash, chorioretinitis, and cerebral calcification, with the subsequent development of hydrocephalus, or microcephaly, a not uncommon result. While the congenital forms of toxoplasmosis have continued to be a striking manifestation of this infection, it has become increasingly apparent that the acquired postnatal form is common, and that the manifestations of this infectious process may vary widely: from inapparent infection to definite clinical disease, which includes meningoencephalitis, glandular involvement, or eye involvement. Clinical manifestations in some instances may simulate those of the rickettsial diseases. A practical classification of toxoplasmic infection in human subjects, suggested by Beckett and FIynn 2 in 1953, serves to emphasize the wide variety of clinical manifestation for which the toxoplasma organism may be responsible: (1) a silent infection essentially asymptomatic; (2) a mild grippe-like infection similar in some
respects to nonparalytic poliomyelitis; (3) a mild infection simulating infectious mononucleosis which is characterized by enlarged glands and slow convalescence, with eventual complete recovery, and with negative PaulBunnell test; (4) chorioretinitis; (5) an acquired systemic infection occurring in adults and children which gives rise to signs and symptoms of widespread disease. In this last category, the illness may be characterized by a rash which spares the scalp, palms of the hands, and soles of the feet, suggestive of acute rickettsial infection; by an encephalitis without visceral involvement; by chorioretinitis; or by a febrile illness suggesting widespread collagen disease. Congenital toxoplasmosis, discussed by these authors as a separate category, is divided further into two essential types with allowance for overlapping manifestations: (a) a severe febrile illness beginning in the immediate neonatal period with vomiting, convulsions, and nystagmus, followed by progressive hydrocephalus, ehorioretinitis, and cerebral calcification, which is characteristically diffuse and spotty; and (b) predominant perinatal manifestations similar to those seen in erythroblastosis fetalis : jaundice and hepatosplenomegaly. Of particular interest to the cliniciar~ is a glandular form of toxoplasmic disease, reported currently in medical literature, which contributes significantly to the etiologic diagnosis of lymphadenopathy of unknown origin. In Denmark, Slim 3 has encountered over 100 such cases, and estimates that toxoplasma infection 388
COMMENTS ON CURRENT LITERATURE
accounts for about 5 pe r cent of the cases of lymphadenopathy of unknown origin. In a recent issue of Lancet a report from the University of Sheffield appears; this report by Beverley and Beattie 9 is entitled "Glandular Toxoplasmosis : A Survey of Thirty Cases." Earlier studies by Beattie 5 which were based on antibody titers had indicated that in the areas surveyed subclinical infection with toxoplasma was relatively common. In Lincolnshire, for example, 36 per cent of the country-dwellers and 22 per cent of the town-dwellers had dye-test antibodies (Sabin-Feldman) to a titer of 1:16, or higher. In the more recent clinical studies also, Beverley and Beattie made use of the Sabin-Feldman 6 dye test for the diagnosis of active infection, following the principle that the dye-test titer should increase eight-fold, or more, at least to a level of 1:256. In the presence of active infection, the titer will be maintained at or near this level for several weeks. ~[n addition to the dye test, the authors have employed complement-fixation antibody procedures f or verification, and state that " t h e level of the complement-fixing antibody should either change from negative to positive and rise to a titre of 1/s, or, if positive initially, should subsequently increase at least four-fold. ''~ For purposes of this recent clinical study, Beverley and Beattie adopted an arbit r a r y level of 1:256 for the dye-test titer, and a complement-fixation titer of 1:10, the results obtained being correlated wherever possible with search for the toxoplasma organism. In 4 of the 30 cases described, toxoplasma organisms were isolated from excised glandular tissue by the inoculation of mice. As the authors emphasize, these organisms when obtained from man often prove of low virulence for laboratory animals. However, in some instances in which the animals are free of objective signs, toxoplasmic cysts may be seen in the brains of inoculated animals for as long as a month, or more, after inoculation. This problem of low virulence
3~9
in relation to exact etiologic diagnosis may be solved to some extent by the use of methods more recently developed: inoculation of the embryonatcd egg and of tissue culture preparations.' It is difficult also to detect the parasite in stained sections of lymph glands excised from human subjects; after long search Stanton and Pinkerton s were able to report the finding of one cyst. Likewise, the pathologic changes observed in human lymph nodes are not characteristic, being described in some instances as a "lymphohistiocytic medullary retieulosis," and in others as a "focal medullary reticulosis." In the cases of glandular toxoplasmosis reported currently, the initial clinical diagnosis most commonly considered was that of infectious mononucleosis. Other clinical impressions included tonsillitis, mumps, Hodgkin's disease, lymphosarcoma, leukemia, aleukemic leukemia, and poliomyelitis, indicating that the clinical manifestations are so varied as to be of little aid in diagnosis. None of the patients with glandular toxoplasmosm showed a positive Paul-Bunnell reaction. The age incidence is of interest: 10 of the 30 patients were under the age of 10 years, 11 patients were between the ages of 11 and 20 years, 4 patients ranged in age from 20 to 30 years, a~d 5 of the 30 patients were over 30 years of age. This age distribution is similar to the age incidence of infectiot~s mononucleosis in children and young adults. The clinical manifestations of the disease process varied greatly in severity and duration. Some were never ill; others complained that they were " be l ow p a r " for weeks. In 20 of the 30 patients, swelling and pain in the lymph glands (usually cervical) were noted initially. As a rule, these enlarged glands regressed vei:y slowly, sometimes requiring many months for return to normal size. Sore throat, which was not a prominent symptom, was noted initially in only 7 patients, but developed later in the course in 3 others. Other symptoms
390
THE
J O U R N A L OF P E D I A T R I C S
included severe headache, fatigue, depression, and muscle pain. From the clinical point of view, it is of interest that none of the 30 patients experienced high fever and 11 of them were afebrile. In some patients, pain in the neck and the back led to the suspicion of poliomyelitis, and in other instances meningismus was suspected. Several complained of pain in the joints and limbs and in some abdominal pain was present, suggesting some degree of mesenteric lymphadenitis. Fatigue was a common manifestation, and in some instances was long continued. Blood studies in 6 patients revealed an absolute leukocytosis; in 15 patients lymphocytosis was observed, and in 6, cells of the glandular-fever type were reported. In only one instance was there any suggestion of pulmonary involvement, and in one other instance enlarged hilar nodes were noted on x-ray examination. No serious sequelae were reported in this se~'ies of 30 patients. The source of infection in human toxoplasmosis is not known definitely ; animals have been suspected, since the organism is to be found in many animals and birds potentially associated with man: the gondi in Africa; mice, rats, rabbits, guinea pigs, squirrels, foxes, mink, chinchilla, dogs, cats, swine, sheep, cattle, various primates, as well as pigeons, chickens, ducks, and penguins2 The animals most commonly suspected are dogs, cats, and rabbits. In the series of patients with glandular toxoplasmosis currently reported from England, 4 21 had association with dogs, in some instances close contact; 12 with cats, and 5 with budgerigars, a psittaeine bird becoming increasingly popular as a pet. The significance of close association with animals or birds is indicated by the known occurrence of toxoplasma organisms in the droppings of birds, in the urine, feces, and saliva of animals, and also in the saliva of man. While the route of invasion in man is not known, it has been suggested that the organism may gain access to the body through the mucous membrane of the
tonsillo-pharyngeal region, since cervical adenopathy is a common manifestation. The widespread occurrence of toxoplasma infection in the human subject is reflected by surveys carried out on the human population in various parts of the world. Such a survey reported recently from the Toronto area by Harper, Ormsby, and Coekeram 1~ indicates that positive skin test for toxoplasmin increases with age from about 10 per cent positive in the youngest age group studied to 40 per cent positive in the older age group. Also, the presence of complement-fixing antibodies in normal members of the population in this area would indicate that inapparent and unrecognized toxoplasmic infections are widespread. Thus, it appears that human infection with toxoplasma organisms is more common than has been supposed heretofore. Lymphadenopathy as a clinical manifestation appears to be one of the more common forms of acquired toxoplasmosis, and it seems reasonable that the various diagnostic tests for toxoplasmosis are indicated whenever the clinician encounters an unusual form of glandular involvement in the human subject. Since inapparent infection in the pregnant woman may result in abnormalities in the fetus, diagnosis would be of particular value in this group. The treatment of toxoplasmic infections has not been entirely satisfactory; reports in the literature, however, suggest that a combination of sulfadiazine and pyrimethamine, or triple sulfonamides plus pyrlmethamine may be of value. 4, 9 Since pyrimethamine is a folie acid antagonist, and severe leukopenia may result from its use, leukocyte counts should be checked at frequent intervals in order to detect any adverse reaction to this drug. The prevalence of toxoplasma infection among animals and birds would suggest that careful scrutiny be given the possible animal sources of human toxoplasmosis, particularly household pets. The recognition of toxoplasmosis as an infection widespread in the
COMMENTS ON CURRENT LITERATURE
human population, and current emphasis on the protean manifestations of this disease, including glandular involvement, particularly in the cervical region, should alert the clinician to this diagnostic possibility whenever unusual cases of glandular fever are encountered.
4. 5.
RUSSELL J. BLATTNER REFERENCES 1. Wolf~ A., Cowen, D., a n d Paige, B. H.: H u m a n Toxoplasmosis: Occurrence in I n f a n t s as an Encephalomyelitis; Verification b y Transmission to Animals, Science 89: 226~ 1939. Toxoplasmlc Encephalomyelitis: A New Case of Granulomatous Encephalomyelitis Duo to a Protozoan, Am. J. Path. 15: 657~ 1939. Toxoplasmie Encephalomyelitis: Experimental Transmission of I n f e c t i o n to Animals F r o m a H u m a n I n f a n t , J. Exper. Med. 71: 187, 1940. Sabin, A . B . : Biologic and Immunological I d e n t i t y of Toxoplasma of Animal and H u m a n Origin, Prec. Soc. Exper. Biol. & Med. 41: 75, 1939. 2. Beckett, R. S., and F l y n n , F. J., Jr.: Toxoplasmosis: Report of Two New Cases, W i t h a Classification and W i t h a Demonstration of the Organisms in the H u m a n Placenta, New England J. Med. 249: 345, 1953. 3. Slim, J. C.: Toxoplasma Acquisita Lymphonodosa: Clinical and Pathological Aspects, Ann. New York Acad. Sc. 64: 185, 1956. Conference on Clinical
6.
7.
8.
9. 10.
391
Aspects and Diagnostic P r o b l e m s of Toxoplasmosis in Paediatrics, E i g h t h I n t e r n a t i o n a l Congress of Paediatrics, Copenhagen, Denmark, July 25 to 26, Discussion-Vol., Copenhagen, Denmark, Berlingska Boktryckeriet, 1956, p. 40]. Beverley, J-. K. A., and Beattie, C. P.: Glandular Toxoplasmosis: A S u r v e y of T h i r t y Cases~ Lancet 2: 379, 1958. Beattie, C. P.: Clinical and Epidemiological Aspects of Toxoplasmosis, Tr. Roy. Soc. Trop. Med. & Hyg. 51: 96, 1957. Sabin, A. B., and Feldman, H. A.: Dyes as Microchemical I n d i c a t o r s of a New I m m u n i t y Phenomenon Affecting a Protozoan P a r a s i t e (Toxoplasma), Science 108: 660, 1948. Chernin, E., and Weller, T. H.: Serial Propagation of Toxoplasma gondii in Roller Tube Cultures of Mouse and Human Tissues, Prec. Soc. Exper. Biol. & Med. 85: 68, 1954. F u r t h e r Observations on the G r o w t h of Toxoplasma gondii in Roller Tube Cultures of Mouse aud Primate Tissues, J. Parasitol. 43: 33, 1957. Balducci, D., and Tyrrell, D.: Quantit a t i v e Studies of Toxoplasma gondii in Culture of Trypsin-Dispersed Mammalian Cells, Brit. J. Exper. Path. 37: 168, 1956. Stanton, M. F., and Pinkerton, H.: Benign Acquired Toxoplasmosis W i t h Subsequent Pregnancy, Am. J. Clin. P a t h . 23: 1199, 1953. Feldmau, H. A.: Toxoplasmosis: Review Article, P e d i a t r i c s 22: 559, 1958. Harper, D. W., Ormsby, H. L., and Cockeram, A.: A Su'rvey of Skill and Complement F i x a t i o n Tests for Toxoplasmosis in the Toronto Area, Canad. M. A. J. 79: 25, 1958.