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Fowl Leukosis
Fowl Leukosis V. TRANSMISSION E X P E R I M E N T S * C. D . L E E Veterinary Research Institute AND
(Presented at Annual Meeting August 1938; Received for publication October 3, 1938)
I
N CONDUCTING transmission experiments with a disease such as fowl leukosis, it seems of prime importance that one should have definite knowledge of the origin of the chicks used for injection. The birds used in these experiments were hatched at the laboratory from our own breeding flocks, kept solely for this purpose. A definite mating and hatching, as well as family record, was available for each chick. The chicks from each hen were separated into a series, that is, one chick for injection, one for contact and one for a control. In the event any cases of leukosis developed in the breeding flock during the experiment the chicks from this hen were immediately removed from the experiment and are not tabulated in the results. This precaution was solely to eliminate the possibility of spontaneous cases in our experimental birds. The controls were kept on a separate part of the farm, far from any other chickens and were cared for by a caretaker who had no contact with other chickens. The birds were taken directly from the incubator to the brooder houses which were equipped with screen porches and at no time were birds allowed to be on the ground. It is quite generally agreed tht the younger birds are * Joint contribution from the Veterinary Research Institute and the Iowa Agricultural Experiment Station. Journal Paper No. J638 of the Iowa Agricultural Experiment Station. Project No. 61.
more suceptible than older birds, therefore it is very essential chicks must be injected at a very early age. In these experiments all birds were injected when one week to ten days old. Blood counts, differential smears and hemoglobin determinations were made weekly on all birds in the experiments, as well as control. At the end of the fourteen months' period all experimental birds that did not die or were not killed because of symptoms, were sacrificed and a complete histopathological examination was made. Transmission experiments herein recorded are with tissues other than blood. The birds used in these experiments were Leghorns and are designated as susceptible and resistant, since there appears to be a distinct difference in the susceptibility and resistance of the different families in this flock. EXPERIMENT I
Transmission by Injection and Pen Contact A saline suspension was made from an enormous ovarian tumor from a pullet that showed no eye or nerve lesions. The bone marrow appeared normal as was the blood picture. Histologically the cells were variable in size and shape and were principally undifferentiated blast cells (Hemocytoblasts). Group 1 contained forty susceptible Leghorns, which were placed in the house as
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H . L . WlLCKE Iowa Agricultural Experiment Station, Iowa State College
FOWL LEUKOSIS—TRANSMISSION EXPERIMENTS
12 birds (30 percent of the total of 40 became affected. In the injected group, 8 birds (40 percent), and in the contact group, 4 birds (20 percent) became affected. The positive cases include erythroleukosis 2' cases; eye type 1 case; nerve type 2 cases; myeloid leukosis 2 cases; hemocytoblastosis 2 cases; and lymphocytoma 3 cases. The experiment with this group indicates a wide difference in susceptibility and resistance as compared to group 1. It is also worthy of note that as in group 1 many various manifestations were produced by a single inoculum. The 15 birds used as controls in this experiment showed no evidence of disease over the fourteen months' period. EXPERIMENT II
Transmission by Injection and Pen Contact A tissue suspension in saline solution was made of two markedly enlarged and infiltrated ischiatic nerves and used as inoculum for groups 3 and 4. The tissue was obtained from a 9 months' old cockerel suffering from a complete paralysis of both legs. The bird had been paralyzed for 22 days, and was extremely emaciated and weak. The blood smears over a period of 10 days were normal and upon autopsy no gross lesions were noted except in the ischiatic nerves which were greatly enlarged, edematous, soft, yellow grey in appearance and showing visible cross striatums. Group 3 was composed of 40 susceptible Leghorns of which 20 were inoculated intraperitoneally with 2 cc. of the inoculum when 1 week old. The remaining 20 birds were left uninoculated for pen exposure contact. From the data collected from group 3 over a fourteen months' period, it was found 24 (60 percent) of the 40 birds
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on June 7, 2015
soon as taken from the incubator. Twenty of these birds were inoculated intraperitoneally with 2 cc. of the inoculum when they were one week old. The remaining twenty birds were left uninoculated solely for pen exposure contact. In data collected from this group over a fourteen months' period it was found 70 percent of the total 40 birds became affected. In the injected group, 18 birds (90 percent), and in the pen exposure contact group, 10 birds (50 percent) became affected. The positive cases recorded include practically all the previously mentioned manifestations, namely, nerve type 6 cases; eye type 2 cases; erythroleukosis 4 cases; myeloid leukosis 3 cases; hemocytoblastosis 4 cases and lymphocytoma 9 cases. This experiment indicates that the etiological agent or agents were present in this suspension of ovarian tumor tissue, and that erythroleukosis, myeloid leukosis, iritis, hemocytoblastic and lymphocytic infiltrations of nerves causing paralysis and tumors were produced by the same inoculum. The disease was transmitted by intraperitoneal injection of affected tissue suspensions into young chicks and to a less extent by pen contact exposure. In general there was a difference in time element between injected and contact groups, the contact group taking a longer time. Twenty birds of the same age and pedigree were used as controls. None of these birds became affected during the fourteen months of the experiment. Group 2, composed of forty birds of a resistant strain of White Leghorns, were inoculated intraperitoneally with 2 cc. of the same inoculum as was used in group 1. The birds were of the same age and cared for in the same manner as was group 1. In data collected from group 2 over a fourteen months' period, it was found that
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EXPERIMENT III A tissue suspension was made from an enormously enlarged liver of a bird that had been injected six months previously with a saline tissue suspension of a large ovarian tumor. The liver was grey in color, very friable, soft-lymphoid-like in character. When a section was cut the grey infiltrative process was found to extend throughout the entire organ. Histologically the cells were variable in size and many mitotic figures were observed. Some of the cells were definitely lymphocytes but a majority were in the undifferentiated blast stage and were regarded as hemocytoblasts. The blood picture of this bird had been normal over the inoculation period and the last differential smear was made four days before the bird died. The spleen was moderately enlarged as was the kidneys. In group 5, 20 susceptible Leghorns were inoculated intraperitoneally with 2 cc. of this material when one week old, and 20 chicks were left uninoculatd for pen exposure contact. In data collected over a fourteen months' period it was noted 20 (50 percent) of the birds became affected. In the injected group, 15 birds became affected while in the pen exposure group only 5. The positive cases observed were nerve type 2 cases; eye type 2 cases; erythroleukosis 2 cases; myeloid leukosis 3 cases; hemocytoblastosis 4 cases and lymphocytoma 7 cases. The controls, numbering 20 birds, remained healthy during the entire period. In group 6, 20 resistant Leghorns were inoculated with the same material as in group 5 and 20 birds were left uninoculated for pen contact exposure. The data obtained from this group over a period of fourteen months showed that only 6 (15 percent) out of 40 birds became infected.
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on June 7, 2015
became affected. In the injected group, 16 (80 percent) of the birds were affected. In the pen contact group, 8 (40 percent) of the birds were affected. The positive cases recorded include practically all the previously mentioned manifestations, namely, nerve type 4 cases; eye type 2 cases; erythroleukosis 2 cases; myeloid leukosis 5 cases; hemocytoblastosis 4 cases and lymphocytoma 7 cases. The controls of this group, IS in number, remained healthy and no cases developed over the fourteen months' period. Group 4 contained 40 resistant Leghorn chicks of which 20 were inoculated intraperitoneally when 1 week old with 2 cc. of the same inoculum as was used in group 3. The remaining 20 birds were left uninoculated solely for pen exposure contact. In data collected from group 4 over a fourteen months' period it was found, 8 (20 percent) of the 40 birds became affected. In the injected group, 6 (30 percent) became affected and in the pen contact exposure group, 2 (10 percent) were affected. The positive cases in group 4 were— nerve type 2 cases; eye type 1 case; erythroleukosis 1 case; myeloid leukosis 1 case; hemacytoblastosis 2 cases and lymphomatosis 1 case. The controls of this group, 15 birds in number, remained healthy during the fourteen months. This experiment indicates that the transmitting agent was present in the affected nerve and that erythroleukosis, myeloid leukosis, paralysis, iritis, lymphocytic and hemocytoblastic infiltrations and tumors were produced by a single inoculum. In general, as in Experiment I, there was a difference in time element between the inoculated and pen contact group, the contact group taking a little longer. There was a wide difference in susceptibility and resistance in groups 3 and 4.
FOWL LEUKOSIS—TRANSMISSION EXPERIMENTS
EXPERIMENT IV Transmission by Injection and Pen Contact—Berkejeld Filtrate, Ovarian Tumor A saline suspension of the same ovarian tumor, as used in Experiment I, was passed through a glass funnel packed with moist filter paper. The filtered material was then centrifuged and the supernatant fluid was passed through a Berkefeld 3N filter. Nineteen Leghorn chicks when one week old were injected intraperitoneally with 2 cc. of this material. Seventeen chicks in this group were left uninoculated for pen contact exposure. In the data collected from Experiment IV over a period of fourteen months, it was noted 12 of the 36 birds (33 1/3 percent) became affected. In the injected group, 8 of the 19 birds (42 percent) were affected and 4 of the 17 birds (25 percent) in the pen contact exposure group. The positive cases recorded include practically all of the manifestations previously mentioned. The positive cases in the injected group include lymphomatosis 2; myeloid leukosis 1; erythroleukosis 2; paralysis (nerve type) 1; hemocytoblastosis 2. The positive cases recorded in the pen
contact exposure group include lymphomatosis 1; myeloid leukosis 1; erythroleukosis 1; hemocytoblastosis 1. This experiment indicates that the etiological agent is present in filtrates of affected organs. The percentage of birds becoming affected was considerably less when filtrates were used than when tissue extracts were used. In general, the incubation time was longer with filtrates than with tissue extracts and was also longer in case of pen exposure contact birds as compared with inoculated birds. This experiment, as Experiment I, shows that the various manifestations such as erythroleukosis, myeloid leukosis, hemocytoblastic and lymphocytic infiltrations causing paralysis and tumor formation, were produced by the same inoculum, this material being a filtrate of an ovarian tumor. The 17 birds of the same age and pedigree used in the control group remained unaffected for a period of fourteen months. EXPERIMENT V Transmission by Litter Exposure Contact The house used for this group had been used previously for transmission groups and had housed numerous birds showing the various manifestations of fowl leukosis. The litter, which was ground cobs, and the droppings were not removed from this house during the previous experiments and were allowed to accumulate for two years. The litter was about six inches deep in the house and the only preparation of this house was to rake the litter and dry it. Thirty chicks of a susceptible strain were placed in this house when taken from the incubator on April 30, 1934. The tabulations were made over a period of 19 months and birds that were not autopsied appeared in perfect health. Differential smears as well as blood counts were performed on all birds classified as
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on June 7, 2015
The positive cases were erythroleukosis 1 case; myeloid leukosis 1 case; nerve type 1 case; lymphocytoma 2 cases and myelocytoblastosis 1 case. The controls of this experiment, 20 in number, remained healthy throughout the fourteen months' period. This experiment indicates that the saline suspension of a lymphomatosis liver contained the transmitting agent. It also indicates that the various manifestations of this disease may be transmitted from a single etiological agent. It also indicates that as in Experiments I and II there is a great deal of difference in resistance and susceptibility of different families of a strain of birds.
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C. D. LEE AND H. L. WILCKE
SUMMARY AND CONCLUSIONS 1. The term, fowl leukosis, is used to
include in common the group of transmissible leukemic, aleukemic, and leukemic-like dieases of fowls. 2. The disease in all expressions may be transmitted to healthy chicks by injection of tissue suspensions of affected organs, by injection of cell-free filtrates, by pen contact exposure or by contact with contaminated soil or litter. 3. The evidence indicates that fowl leukosis is an infectious disease and transmitted by a filterable virus. 4. The incubation period of the disease is rather long, with a majority of cases occurring between four and eight months. The clinical course is variable, extending over a period of weeks or months in some cases, while in others it is comparatively short. No recoveries have been observed but temporary respites do occur. 5. In the light of our present knowledge it seems rather important that a complete histopathological examination be made of all birds before a definite diagnosis is made. 6. The injection of a suspension made from one type produces all the various manifestations considered to be expressions of this disease. Different suspensions experimentally produce similar results. 7. Neurolymphomatosis associated with iritis, hemocytoblastosis, lymphoid, erythroid and myeloid types of leukosis, are different expressions of the same disease and all are transmitted by a common etiologic agent. 8. There seems to be a definite inherent difference of susceptibility and resistance in different birds and birds of different strains. 9. The most important methods of control are careful culling, sanitation and use of breeding stock from resistant sources.
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on June 7, 2015
negative before they were allowed to be put in this classification. It is to be noted that 15 birds, or 50 percent of the entire group, became affected during the nineteen months' period. It is also interesting to note that, as in the other experiments, practically all the various forms or manifestations occurred. The following different expressions occurred: lymphomatous tumors and infiltrations 3 birds; myeloid leukosis 2 birds; erythroleukosis 2' birds; nerve type 6 birds; eye type 1 bird and 1 bird with a combination of eye type and hemocytoblastosis. This experiment indicates that the infection may be transmitted by contact with contaminated litter or surroundings. This is important to know in instituting effective control measures. It also indicates infection may remain in houses or litter for at least two years and possibly for a much longer time. The controls of this group were kept for 19 months and, of the group of 15 birds, one bird developed a lymphoid-like tumorous mass in the ovary and one a complete paralysis case with infiltration of the ischiatic nerves. In addition to the above experiments in susceptibility and resistance we have had rather direct supervision over some thirtyfive farm flocks. Five years ago the incidence of fowl leukosis with its various manifestations was approximately 25 percent. A careful program of culling, sanitation and breeding for resistance has been carried out. This has been by selection of resistant pullets and by use of two years old birds in the breeding flock. The incidence of fowl leukosis has been reduced to about 1 percent in these flocks.
(Presented at Annual Meeting August 1938; Received for publication October 3, 1938)
I
N CONDUCTING transmission experiments with a disease such as fowl leukosis, it seems of prime importance that one should have definite knowledge of the origin of the chicks used for injection. The birds used in these experiments were hatched at the laboratory from our own breeding flocks, kept solely for this purpose. A definite mating and hatching, as well as family record, was available for each chick. The chicks from each hen were separated into a series, that is, one chick for injection, one for contact and one for a control. In the event any cases of leukosis developed in the breeding flock during the experiment the chicks from this hen were immediately removed from the experiment and are not tabulated in the results. This precaution was solely to eliminate the possibility of spontaneous cases in our experimental birds. The controls were kept on a separate part of the farm, far from any other chickens and were cared for by a caretaker who had no contact with other chickens. The birds were taken directly from the incubator to the brooder houses which were equipped with screen porches and at no time were birds allowed to be on the ground. It is quite generally agreed tht the younger birds are * Joint contribution from the Veterinary Research Institute and the Iowa Agricultural Experiment Station. Journal Paper No. J638 of the Iowa Agricultural Experiment Station. Project No. 61.
more suceptible than older birds, therefore it is very essential chicks must be injected at a very early age. In these experiments all birds were injected when one week to ten days old. Blood counts, differential smears and hemoglobin determinations were made weekly on all birds in the experiments, as well as control. At the end of the fourteen months' period all experimental birds that did not die or were not killed because of symptoms, were sacrificed and a complete histopathological examination was made. Transmission experiments herein recorded are with tissues other than blood. The birds used in these experiments were Leghorns and are designated as susceptible and resistant, since there appears to be a distinct difference in the susceptibility and resistance of the different families in this flock. EXPERIMENT I
Transmission by Injection and Pen Contact A saline suspension was made from an enormous ovarian tumor from a pullet that showed no eye or nerve lesions. The bone marrow appeared normal as was the blood picture. Histologically the cells were variable in size and shape and were principally undifferentiated blast cells (Hemocytoblasts). Group 1 contained forty susceptible Leghorns, which were placed in the house as
[250]
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on June 7, 2015
H . L . WlLCKE Iowa Agricultural Experiment Station, Iowa State College
FOWL LEUKOSIS—TRANSMISSION EXPERIMENTS
12 birds (30 percent of the total of 40 became affected. In the injected group, 8 birds (40 percent), and in the contact group, 4 birds (20 percent) became affected. The positive cases include erythroleukosis 2' cases; eye type 1 case; nerve type 2 cases; myeloid leukosis 2 cases; hemocytoblastosis 2 cases; and lymphocytoma 3 cases. The experiment with this group indicates a wide difference in susceptibility and resistance as compared to group 1. It is also worthy of note that as in group 1 many various manifestations were produced by a single inoculum. The 15 birds used as controls in this experiment showed no evidence of disease over the fourteen months' period. EXPERIMENT II
Transmission by Injection and Pen Contact A tissue suspension in saline solution was made of two markedly enlarged and infiltrated ischiatic nerves and used as inoculum for groups 3 and 4. The tissue was obtained from a 9 months' old cockerel suffering from a complete paralysis of both legs. The bird had been paralyzed for 22 days, and was extremely emaciated and weak. The blood smears over a period of 10 days were normal and upon autopsy no gross lesions were noted except in the ischiatic nerves which were greatly enlarged, edematous, soft, yellow grey in appearance and showing visible cross striatums. Group 3 was composed of 40 susceptible Leghorns of which 20 were inoculated intraperitoneally with 2 cc. of the inoculum when 1 week old. The remaining 20 birds were left uninoculated for pen exposure contact. From the data collected from group 3 over a fourteen months' period, it was found 24 (60 percent) of the 40 birds
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on June 7, 2015
soon as taken from the incubator. Twenty of these birds were inoculated intraperitoneally with 2 cc. of the inoculum when they were one week old. The remaining twenty birds were left uninoculated solely for pen exposure contact. In data collected from this group over a fourteen months' period it was found 70 percent of the total 40 birds became affected. In the injected group, 18 birds (90 percent), and in the pen exposure contact group, 10 birds (50 percent) became affected. The positive cases recorded include practically all the previously mentioned manifestations, namely, nerve type 6 cases; eye type 2 cases; erythroleukosis 4 cases; myeloid leukosis 3 cases; hemocytoblastosis 4 cases and lymphocytoma 9 cases. This experiment indicates that the etiological agent or agents were present in this suspension of ovarian tumor tissue, and that erythroleukosis, myeloid leukosis, iritis, hemocytoblastic and lymphocytic infiltrations of nerves causing paralysis and tumors were produced by the same inoculum. The disease was transmitted by intraperitoneal injection of affected tissue suspensions into young chicks and to a less extent by pen contact exposure. In general there was a difference in time element between injected and contact groups, the contact group taking a longer time. Twenty birds of the same age and pedigree were used as controls. None of these birds became affected during the fourteen months of the experiment. Group 2, composed of forty birds of a resistant strain of White Leghorns, were inoculated intraperitoneally with 2 cc. of the same inoculum as was used in group 1. The birds were of the same age and cared for in the same manner as was group 1. In data collected from group 2 over a fourteen months' period, it was found that
251
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C. D. LEE AND H. L. WILCKE
EXPERIMENT III A tissue suspension was made from an enormously enlarged liver of a bird that had been injected six months previously with a saline tissue suspension of a large ovarian tumor. The liver was grey in color, very friable, soft-lymphoid-like in character. When a section was cut the grey infiltrative process was found to extend throughout the entire organ. Histologically the cells were variable in size and many mitotic figures were observed. Some of the cells were definitely lymphocytes but a majority were in the undifferentiated blast stage and were regarded as hemocytoblasts. The blood picture of this bird had been normal over the inoculation period and the last differential smear was made four days before the bird died. The spleen was moderately enlarged as was the kidneys. In group 5, 20 susceptible Leghorns were inoculated intraperitoneally with 2 cc. of this material when one week old, and 20 chicks were left uninoculatd for pen exposure contact. In data collected over a fourteen months' period it was noted 20 (50 percent) of the birds became affected. In the injected group, 15 birds became affected while in the pen exposure group only 5. The positive cases observed were nerve type 2 cases; eye type 2 cases; erythroleukosis 2 cases; myeloid leukosis 3 cases; hemocytoblastosis 4 cases and lymphocytoma 7 cases. The controls, numbering 20 birds, remained healthy during the entire period. In group 6, 20 resistant Leghorns were inoculated with the same material as in group 5 and 20 birds were left uninoculated for pen contact exposure. The data obtained from this group over a period of fourteen months showed that only 6 (15 percent) out of 40 birds became infected.
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on June 7, 2015
became affected. In the injected group, 16 (80 percent) of the birds were affected. In the pen contact group, 8 (40 percent) of the birds were affected. The positive cases recorded include practically all the previously mentioned manifestations, namely, nerve type 4 cases; eye type 2 cases; erythroleukosis 2 cases; myeloid leukosis 5 cases; hemocytoblastosis 4 cases and lymphocytoma 7 cases. The controls of this group, IS in number, remained healthy and no cases developed over the fourteen months' period. Group 4 contained 40 resistant Leghorn chicks of which 20 were inoculated intraperitoneally when 1 week old with 2 cc. of the same inoculum as was used in group 3. The remaining 20 birds were left uninoculated solely for pen exposure contact. In data collected from group 4 over a fourteen months' period it was found, 8 (20 percent) of the 40 birds became affected. In the injected group, 6 (30 percent) became affected and in the pen contact exposure group, 2 (10 percent) were affected. The positive cases in group 4 were— nerve type 2 cases; eye type 1 case; erythroleukosis 1 case; myeloid leukosis 1 case; hemacytoblastosis 2 cases and lymphomatosis 1 case. The controls of this group, 15 birds in number, remained healthy during the fourteen months. This experiment indicates that the transmitting agent was present in the affected nerve and that erythroleukosis, myeloid leukosis, paralysis, iritis, lymphocytic and hemocytoblastic infiltrations and tumors were produced by a single inoculum. In general, as in Experiment I, there was a difference in time element between the inoculated and pen contact group, the contact group taking a little longer. There was a wide difference in susceptibility and resistance in groups 3 and 4.
FOWL LEUKOSIS—TRANSMISSION EXPERIMENTS
EXPERIMENT IV Transmission by Injection and Pen Contact—Berkejeld Filtrate, Ovarian Tumor A saline suspension of the same ovarian tumor, as used in Experiment I, was passed through a glass funnel packed with moist filter paper. The filtered material was then centrifuged and the supernatant fluid was passed through a Berkefeld 3N filter. Nineteen Leghorn chicks when one week old were injected intraperitoneally with 2 cc. of this material. Seventeen chicks in this group were left uninoculated for pen contact exposure. In the data collected from Experiment IV over a period of fourteen months, it was noted 12 of the 36 birds (33 1/3 percent) became affected. In the injected group, 8 of the 19 birds (42 percent) were affected and 4 of the 17 birds (25 percent) in the pen contact exposure group. The positive cases recorded include practically all of the manifestations previously mentioned. The positive cases in the injected group include lymphomatosis 2; myeloid leukosis 1; erythroleukosis 2; paralysis (nerve type) 1; hemocytoblastosis 2. The positive cases recorded in the pen
contact exposure group include lymphomatosis 1; myeloid leukosis 1; erythroleukosis 1; hemocytoblastosis 1. This experiment indicates that the etiological agent is present in filtrates of affected organs. The percentage of birds becoming affected was considerably less when filtrates were used than when tissue extracts were used. In general, the incubation time was longer with filtrates than with tissue extracts and was also longer in case of pen exposure contact birds as compared with inoculated birds. This experiment, as Experiment I, shows that the various manifestations such as erythroleukosis, myeloid leukosis, hemocytoblastic and lymphocytic infiltrations causing paralysis and tumor formation, were produced by the same inoculum, this material being a filtrate of an ovarian tumor. The 17 birds of the same age and pedigree used in the control group remained unaffected for a period of fourteen months. EXPERIMENT V Transmission by Litter Exposure Contact The house used for this group had been used previously for transmission groups and had housed numerous birds showing the various manifestations of fowl leukosis. The litter, which was ground cobs, and the droppings were not removed from this house during the previous experiments and were allowed to accumulate for two years. The litter was about six inches deep in the house and the only preparation of this house was to rake the litter and dry it. Thirty chicks of a susceptible strain were placed in this house when taken from the incubator on April 30, 1934. The tabulations were made over a period of 19 months and birds that were not autopsied appeared in perfect health. Differential smears as well as blood counts were performed on all birds classified as
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on June 7, 2015
The positive cases were erythroleukosis 1 case; myeloid leukosis 1 case; nerve type 1 case; lymphocytoma 2 cases and myelocytoblastosis 1 case. The controls of this experiment, 20 in number, remained healthy throughout the fourteen months' period. This experiment indicates that the saline suspension of a lymphomatosis liver contained the transmitting agent. It also indicates that the various manifestations of this disease may be transmitted from a single etiological agent. It also indicates that as in Experiments I and II there is a great deal of difference in resistance and susceptibility of different families of a strain of birds.
253
254
C. D. LEE AND H. L. WILCKE
SUMMARY AND CONCLUSIONS 1. The term, fowl leukosis, is used to
include in common the group of transmissible leukemic, aleukemic, and leukemic-like dieases of fowls. 2. The disease in all expressions may be transmitted to healthy chicks by injection of tissue suspensions of affected organs, by injection of cell-free filtrates, by pen contact exposure or by contact with contaminated soil or litter. 3. The evidence indicates that fowl leukosis is an infectious disease and transmitted by a filterable virus. 4. The incubation period of the disease is rather long, with a majority of cases occurring between four and eight months. The clinical course is variable, extending over a period of weeks or months in some cases, while in others it is comparatively short. No recoveries have been observed but temporary respites do occur. 5. In the light of our present knowledge it seems rather important that a complete histopathological examination be made of all birds before a definite diagnosis is made. 6. The injection of a suspension made from one type produces all the various manifestations considered to be expressions of this disease. Different suspensions experimentally produce similar results. 7. Neurolymphomatosis associated with iritis, hemocytoblastosis, lymphoid, erythroid and myeloid types of leukosis, are different expressions of the same disease and all are transmitted by a common etiologic agent. 8. There seems to be a definite inherent difference of susceptibility and resistance in different birds and birds of different strains. 9. The most important methods of control are careful culling, sanitation and use of breeding stock from resistant sources.
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on June 7, 2015
negative before they were allowed to be put in this classification. It is to be noted that 15 birds, or 50 percent of the entire group, became affected during the nineteen months' period. It is also interesting to note that, as in the other experiments, practically all the various forms or manifestations occurred. The following different expressions occurred: lymphomatous tumors and infiltrations 3 birds; myeloid leukosis 2 birds; erythroleukosis 2' birds; nerve type 6 birds; eye type 1 bird and 1 bird with a combination of eye type and hemocytoblastosis. This experiment indicates that the infection may be transmitted by contact with contaminated litter or surroundings. This is important to know in instituting effective control measures. It also indicates infection may remain in houses or litter for at least two years and possibly for a much longer time. The controls of this group were kept for 19 months and, of the group of 15 birds, one bird developed a lymphoid-like tumorous mass in the ovary and one a complete paralysis case with infiltration of the ischiatic nerves. In addition to the above experiments in susceptibility and resistance we have had rather direct supervision over some thirtyfive farm flocks. Five years ago the incidence of fowl leukosis with its various manifestations was approximately 25 percent. A careful program of culling, sanitation and breeding for resistance has been carried out. This has been by selection of resistant pullets and by use of two years old birds in the breeding flock. The incidence of fowl leukosis has been reduced to about 1 percent in these flocks.