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Avian Pneumoencephalitis (Newcastle Disease) in the California Official Egg Laying Contest During the 1947-48 Test Year
RESEARCH NOTES
307
AVIAN PNEUMOENCEPHALITIS (NEWCASTLE DISEASE) IN THE CALIFORNIA OFFICIAL EGG LAYING CONTEST DURING THE 1947-48 TEST YEAR J. R. BEACH Department of Veterinary Science, University of California, Berkeley (Received for publication December 22, 1948)
Careful inspection of each entry on arrival at the Contest did not reveal evidence of the presence of any disease among them. On October 28, four weeks later, a sudden and marked drop in the egg yield of pen 15 in house A caused the presence of pneumoencephalitis (PE) to be suspected. A week later, Nov. 3, pen 36 in house B suffered a like decline in production. Between Dec. 10 and Jan. 10, three more pens in House A and two in House B were suspected to have become affected. A blood sample for hemaglutination-inhibition test (HI), a procedure used in the diagnosis of PE, was now taken from one bird selected at random from each of the 7 suspected pens. The blood of the birds from 6 pens gave a positive reaction for PE and one was negative. .
during the latter part of March. HI tests of blood samples from this pen were negative. A companion entry from the same source in pen 32 which had not shown evidence of illness at any time, however, was tested and found, positive for PE. These results indicated that the sickness in pen 33 was not due to PE and that pen 32 had had subclinical infection. At this time blood samples were taken from 3 other pens selected at random. Two of these were PE positive and one was negative. This brought the number of pens tested up to 12, of which 9 were positive to the HI test for PE and 3 were negative.
On Sept. 28, two days before the close of the test year, blood samples for HI test were taken from 3 birds of each entry. The results of these tests for PE were as follows: The blood samples from the 3 pens which had been negative and from the 9 pens which had been positive to HI tests in January or March were, respectively, still negative and positive. Of the 26 pens not previously tested for HI antibodies all of the 3 blood samples from each of 12 pens were positive, one of the 3 blood samples from each of 6 pens was positive, and all of the 3 blood samples from each of 13 pens were negative. Thus the results of the HI tests show that all or part of the birds in 22 of the 38 pens at sometime had been infected with PE, but they do not indicate whether The next cause for suspecting the pres- the infection occurred before or after the ence of PE was dullness, inappetence, and birds arrived at the Contest. However, if drop in egg yield of the birds in pen 33 one assumes that all birds coming from
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 31, 2015
The chicken population consisted of 38 entries of 26 pullets each, a total of 988; there were 2 entries from each of 6 farms, and 3 and 4 entries respectively from each of two farms. Twenty-six entries were of California origin; 12 came from breeders in 7 widely scattered states. The entries were confined separately in 38 pens, without yards, distributed equally in two houses (A & B). The pens were separated by a solid wood partition which prevented all direct contact between birds of different entries. The only access to any pen was by a door at the front. This was kept locked day and night and only caretakers were permitted to enter.
308
RESEARCH NOTES
The fact that 16 of the entries appear to have escaped infection entirely shows that the segregation provided by the solid partitions between pens and/or the operational procedures followed had been effective to an appreciable degree in preventing the spread of a highly contagious disease. The influence of the disease on the performance of the entries involved is difficult to evaluate because there is no certain means of estimating what their total egg yield would have been if they had not been affected. Comparison of records of the 2 pens of the double entries proved of little help. In 2 cases the performance of the infected pen exceeded that of noninfected pen, and in one instance the positions of the infected and non-infected pens were reversed; in one instance in which both pens of a single breeder were infected their final places were the 15th and 30th. The egg yield of a majority of the infected pens did temporarily decline, however, and two pens did not again lay at the pre-infection rate. On the whole, however, the loss in eggs from the effect of the disease did not appear to affect materially the total production for the test year. There were no
deaths definitely attributable to PE although there were 2 in one entry which might have been. This mild outbreak of PE presents some unusual features. The most striking of these, perhaps, is the fact that, on the basis of the results of HI tests, 16 of the 38 entries did not become infected. The complete separation of each entry from others provided by the solid doorless par- r titions between pens undoubtedly acted as a barrier to the spread of infection by direct contact between diseased and susceptible entries. This factor conceivably may also have been an obstacle to transmission of infection by the air-borne route between the pens and perhaps also between houses. One can only speculate on this point, however, because too little is known of the route of travel of air currents by which infection-laden dust would be carried. In no wise affected, however, was the possibility of mechanical transfer of infection by caretakers whose duties required them to enter each pen several times each day. Another somewhat surprising finding is the fact that, on the basis of the results of the HI tests, the infection in some pens did not involve all of the birds. This is quite contrary to concept commonly held that although an outbreak of PE may cause no death loss the morbidity is likely to be 100 percent. Observations made of this outbreak concur with those of outbreaks on poultry farms in demonstrating that a flock of laying pullets can experience PE infection without an appreciable loss from any cause resulting therefrom. They also show that it might be possible, although perhaps not practicable, for poultry raisers to provide housing facilities and adopt operational procedures which would enable them to confine any PE infection that may appear to a relatively small part of their flocks.
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 31, 2015
flocks which had gone through an outbreak of PE before the entries were selected would have been infected, it appears then that much of the infection detected by the HI test at the contest had actually resulted from spread from the 2 pens initially infected. This is shown by the fact that positive reactors to the HI test were found in only one pen of each of 4 of the 6 double entries, in only one pen of the one triple entry, and in only 2 pens of the quadruple entry. The source of the infection at the Contest is unknown, but two possibilities are, that one or more entries had undetected subclinical infection on arrival, or that chance introduction of the virus from the outside had occurred.
307
AVIAN PNEUMOENCEPHALITIS (NEWCASTLE DISEASE) IN THE CALIFORNIA OFFICIAL EGG LAYING CONTEST DURING THE 1947-48 TEST YEAR J. R. BEACH Department of Veterinary Science, University of California, Berkeley (Received for publication December 22, 1948)
Careful inspection of each entry on arrival at the Contest did not reveal evidence of the presence of any disease among them. On October 28, four weeks later, a sudden and marked drop in the egg yield of pen 15 in house A caused the presence of pneumoencephalitis (PE) to be suspected. A week later, Nov. 3, pen 36 in house B suffered a like decline in production. Between Dec. 10 and Jan. 10, three more pens in House A and two in House B were suspected to have become affected. A blood sample for hemaglutination-inhibition test (HI), a procedure used in the diagnosis of PE, was now taken from one bird selected at random from each of the 7 suspected pens. The blood of the birds from 6 pens gave a positive reaction for PE and one was negative. .
during the latter part of March. HI tests of blood samples from this pen were negative. A companion entry from the same source in pen 32 which had not shown evidence of illness at any time, however, was tested and found, positive for PE. These results indicated that the sickness in pen 33 was not due to PE and that pen 32 had had subclinical infection. At this time blood samples were taken from 3 other pens selected at random. Two of these were PE positive and one was negative. This brought the number of pens tested up to 12, of which 9 were positive to the HI test for PE and 3 were negative.
On Sept. 28, two days before the close of the test year, blood samples for HI test were taken from 3 birds of each entry. The results of these tests for PE were as follows: The blood samples from the 3 pens which had been negative and from the 9 pens which had been positive to HI tests in January or March were, respectively, still negative and positive. Of the 26 pens not previously tested for HI antibodies all of the 3 blood samples from each of 12 pens were positive, one of the 3 blood samples from each of 6 pens was positive, and all of the 3 blood samples from each of 13 pens were negative. Thus the results of the HI tests show that all or part of the birds in 22 of the 38 pens at sometime had been infected with PE, but they do not indicate whether The next cause for suspecting the pres- the infection occurred before or after the ence of PE was dullness, inappetence, and birds arrived at the Contest. However, if drop in egg yield of the birds in pen 33 one assumes that all birds coming from
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 31, 2015
The chicken population consisted of 38 entries of 26 pullets each, a total of 988; there were 2 entries from each of 6 farms, and 3 and 4 entries respectively from each of two farms. Twenty-six entries were of California origin; 12 came from breeders in 7 widely scattered states. The entries were confined separately in 38 pens, without yards, distributed equally in two houses (A & B). The pens were separated by a solid wood partition which prevented all direct contact between birds of different entries. The only access to any pen was by a door at the front. This was kept locked day and night and only caretakers were permitted to enter.
308
RESEARCH NOTES
The fact that 16 of the entries appear to have escaped infection entirely shows that the segregation provided by the solid partitions between pens and/or the operational procedures followed had been effective to an appreciable degree in preventing the spread of a highly contagious disease. The influence of the disease on the performance of the entries involved is difficult to evaluate because there is no certain means of estimating what their total egg yield would have been if they had not been affected. Comparison of records of the 2 pens of the double entries proved of little help. In 2 cases the performance of the infected pen exceeded that of noninfected pen, and in one instance the positions of the infected and non-infected pens were reversed; in one instance in which both pens of a single breeder were infected their final places were the 15th and 30th. The egg yield of a majority of the infected pens did temporarily decline, however, and two pens did not again lay at the pre-infection rate. On the whole, however, the loss in eggs from the effect of the disease did not appear to affect materially the total production for the test year. There were no
deaths definitely attributable to PE although there were 2 in one entry which might have been. This mild outbreak of PE presents some unusual features. The most striking of these, perhaps, is the fact that, on the basis of the results of HI tests, 16 of the 38 entries did not become infected. The complete separation of each entry from others provided by the solid doorless par- r titions between pens undoubtedly acted as a barrier to the spread of infection by direct contact between diseased and susceptible entries. This factor conceivably may also have been an obstacle to transmission of infection by the air-borne route between the pens and perhaps also between houses. One can only speculate on this point, however, because too little is known of the route of travel of air currents by which infection-laden dust would be carried. In no wise affected, however, was the possibility of mechanical transfer of infection by caretakers whose duties required them to enter each pen several times each day. Another somewhat surprising finding is the fact that, on the basis of the results of the HI tests, the infection in some pens did not involve all of the birds. This is quite contrary to concept commonly held that although an outbreak of PE may cause no death loss the morbidity is likely to be 100 percent. Observations made of this outbreak concur with those of outbreaks on poultry farms in demonstrating that a flock of laying pullets can experience PE infection without an appreciable loss from any cause resulting therefrom. They also show that it might be possible, although perhaps not practicable, for poultry raisers to provide housing facilities and adopt operational procedures which would enable them to confine any PE infection that may appear to a relatively small part of their flocks.
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 31, 2015
flocks which had gone through an outbreak of PE before the entries were selected would have been infected, it appears then that much of the infection detected by the HI test at the contest had actually resulted from spread from the 2 pens initially infected. This is shown by the fact that positive reactors to the HI test were found in only one pen of each of 4 of the 6 double entries, in only one pen of the one triple entry, and in only 2 pens of the quadruple entry. The source of the infection at the Contest is unknown, but two possibilities are, that one or more entries had undetected subclinical infection on arrival, or that chance introduction of the virus from the outside had occurred.