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Notes
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Here is where, for practical purposes, the study of Newcastle disease began. Some have argued for earlier descriptions of Newcastle disease from Europe and Africa but this is the first well-recognised and easily-retrievable description in English. The outbreak near Newcastle-upon-Tyne, UK, actually occurred in 1926, the year before publication. Two further outbreaks were also reported, one in Somerset and one, involving many farms, in Staffordshire.
Doyle records a number of observations before he describes his experimental work. Contemporary workers would appreciate the problems and recognise the findings that are described.
· Political events (the General Strike in the UK) presented initial access to the index farm.
· Transmission experiments conducted by others (Dr. Clayton and Mr. Howie) indicated an infectious disease with an incubation period longer than that of fowl plague, the important infectious disease recognised at that time.
· When the farm could be visited, Doyle advised destruction of the surviving birds, burning of the carcasses, disinfection of the premises which should then remain empty for "a couple of months" and introduction of a few healthy sentinel birds before complete restocking.
· The spread of the disease with the sale of affected birds through markets.
· Mortalities of 100% on some farms.
· An earlier report of a similar disease in an industry journal.
· Doyle suggested the name Newcastle disease.
· The need to improvise accommodation to isolate experimental birds.
The experimental studies indicated an incubation period of 4 to 11 days with an average of 5 days. The sequence of clinical signs with the experimental disease was fever, refusal to eat, drowsiness, increased respiration, watery diarrhoea and death after 6 to 8 days. Particular mention was made of the respiratory sign with "long gasping inhalation through the half-opened beak". Nervous signs with head movements, lameness and paralysis were also described. Only 6 of the hundreds of experimental chickens survived the infection.
Gross pathological examinations were made on about 200 chickens with Newcastle disease and 100 with fowl plague. It was concluded that there were no characteristic lesions for Newcastle disease. When Doyle failed to find a bacterial cause for the disease, he undertook filtration experiments. Mouth exudate was the favoured source and in one experiment 7 serial passages were performed.
Pigeons, especially young pigeons, were susceptible to experimental infection. These hosts were usually resistant to fowl plague.
Chickens were most readily infected by intravenous inoculation. The disease could also be transmitted by subcutaneous inoculation, skin scarification, conjunctival exposure and introduction into the crop. Intramuscular inoculation gave irregular results.
Experimental inoculation of chickens with homogenates of organs and other materials from affected chickens showed that the infectious agent was widely distributed. Homogenates of mouth exudate diluted as much as 1:2,000,000 were infectious.
Various forms of infectious material were stored (temperature not stated) and injected into chickens. Of interest was the survival of infectivity in 50% glycerine saline for at least 197 days. Some chickens inoculated with "negative" samples were later found to be immune, possibly an early indication of the efficacy of inactivated Newcastle disease vaccines.
It was shown that chickens immune to Newcastle disease were susceptible to fowl plague, and chickens immune to fowl plague succumbed to Newcastle disease. Cross neutralisation tests further indicated the differences between the agents causing these conditions.
Similar in vivo tests were undertaken to test the effect of various disinfectants on infectious material. The virus was more susceptible to alkalis than to acids, and susceptibility to ether was demonstrated.
Doyle was apparently unaware of the study in the Dutch language published the previous year and describing a similar disease in what is now Jakarta in Indonesia.
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