In the study of sporadic bovine encephalitis it has been necessary to propagate the causative agent by animal passage. This has been rather expensive and time consuming where calves were employed and only slightly less so when guinea pigs were used. In an effort to find a more satisfactory method, chick embryos were inoculated with the peritoneal exudates or the ground liver and spleen of guinea pigs killed during the height of the disease. These materials were known to be high in concentration of the infectious agent. The methods of embroyo inoculation were those usually employed

McNutt, S. H.

English

Iowa State University Computer Science Technical Reports

Bovine Encephalitis

In the study of sporadic bovine encephalitis it has been necessary to propagate the causative agent by animal passage. This has been rather expensive and time consuming where calves were employed and only slightly less so when guinea pigs were used. In an effort to find a more satisfactory method, chick embryos were inoculated with the peritoneal exudates or the ground liver and spleen of guinea pigs killed during the height of the disease. These materials were known to be high in concentration of the infectious agent. The methods of embroyo inoculation were those usually employed.</p

McNutt, S.

Digital Repository @ Iowa State University (ISU)

Bovine Encephalitis Sporadic bovine encephalitis proven an infectious disease by use of chick embryo S. H. McNutt, D.V.M. * I N THE study of sporadic bovine en .. cephalitis2 .3 it has been necessary to propagate the causative agent by animal passage. This has been rather expensive and time consuming where calves were employed and only slightly less so when guinea pigs were used. In an effort to find a more satisfactory method, chick embryos were inoculated with the peritoneal exudates or the ground liver and spleen of guinea pigs killed dur-ing the height of the disease. These ma-terials were known to be high in concen-tration of the infectious agent. The methods of embroyo inoculation were those usually employed. First Trials In the first trials, the inoculations were made into the allantoic sac of 6 to 12 day old embryos. Insofar as could be deter-mined, this method of inoculation pro-duced no effect whatever on the embryo or its membranes. If one is to use embryos for propagation of infectious materials, it is highly desirable that the embryos show some recognizable change whereby one can determine whether or not there has been multiplication. This is not always possible, but in order to determine if it could be done in this case, a second method of inoculation was tried. This proved to be satisfactory. The successful method by which the causative agent was cultivated on chick embryos is known as yolk sac inocula-* Veterinary Research Institute. Iowa Stare College. Ames, Iowa. Win ter-I94 I tion 1. The developing embryos were candled at the desired age and the posi-tion of the embryo and the natural air cell were marked. Some workers using this method locate the position of the yolk or yolk sac before inoculation, but this has not been necessary since that portion of the egg lies on the side opposite the actual embryo and at a slightly lower level. Thus, if the position of the embryo is known, the location of the yolk sac is obvious. Eggs with floating or mislocatecl air cells were discarded. A small hole was bored through the shell over the air cell and after the application of a disinfectant to this area, a twenty gauge needle W2.S inserted through the hole and shell mem-branes. The needle was directed toward the side opposite the embryo and an in-jection of not more than 0.2 cc was made at a depth of nearly an inch, after which the eggs were returned to the incubator and candled daily thereafter. Embryos of from six to nine days were employed. The eggs were incubated under good ., hatchery conditions as regards to temper-ature, moisture, rotation of the eggs, etc. The first inoculation of infectious material into embryos made in this manner result-ed in death of about 50% of the embryos within nine days. A mixture of yolk and embryonic fluids from such dead em-bryos was again injected into the yolk of fresh seven day old embryos and in this way the infection has been propagated in series through 48 passages or subcultures. The interval between inoculation and death of the embryo gradually lessened until 707< of the inoculated embrvos died between the third and fourth day~ and all were opened and examined at that time. Occasionally, the concentration of infec-tion in some of the live embryos was so small that death of freshly inoculated em-bryos was delayed, although often such live infected embryos contained as much of the causative agent as did the dead embryos. Inoculated eggs were candled on the first and second day after injection, and all embryos found dead at that time were discarded because such deaths were usually due to accidents or bacterial con-tamination. Cultures and stained smears were made from all embryos in order to eliminate bacterial contamination. Ma-terial from infected embryos was occas-ionally injected into guinea pigs as an added proof that the infectious agent of bovine encephalitis was the cause of the embryo death. Such material has always produced a more severe disease with earlier symptoms than where infectious animal tissues were employed. Such find-ings indicate an increased concentration in the embryos, and tests are now under-way to determine whether or not this is actually true. Results In the study of sporadic bovine en-cephalomyelitis, developing chick em-bryos are also being injected with bac-teria-free filtrates of infectious material to determine whether or not such filtrates contain the causative agent. Guinea pigs have been found to be more satisfactory for such tests, but this may be due to the fact that the guinea pigs are given a relatively large inoculation, whereas the embryo yolk sac inoculations have been small. Chick embryos have also been em-ployed in attempts to assay the concen-tration of infection in various materials. Preliminary trials have given irregular but very promising results. Takes have been obtained when as little as 0.2 cc of a 1: 100,000 dilution have been injected into the yolk sac of developing embryos. When the technic has been worked out, it is thought that takes will be possible when using a dilution of 1: 100,000 or even higher. After showing that sporadic bovine encephalomyelitis was an infectious dis-ease, efforts have been mainly concerned with attempts to identify the infection. v; In this, the encephalomyelitis has been compared with known similar diseases; attempts have been made to grow the causative agent in culture media; 66 material has been stained in an endeavor to find inclusion bodies; filtrations have been made to identify a virus; and chick embryos have been employed. The dis-ease has been shown not to be related to equine encephalomyelitis, Listerellosis, rabies, Aujesky's disease, or malignant catarrhal fever. It has been impossible to grow bacteria from tissues of the affected animals. In culturing, a study using aero-bic methods has been quite exhaustive. Trials by anaerobic methods have not been so complete, but all those so far em-ployed have been equally negative. Efforts to stain inclusion bodies like those seen in some virus diseases, but especially those found in the Rickettsia diseases and in contagious pleuro-pneumonia, have met with total failure. Thus, attempts to iden-tify the causative agent by the above three methods have failed. Infectious material has been passed through the coarse and medium grades of Berkefeld filters. This has resulted in 19 filtrates that were con-sidered satisfactory. Nine of these gave positive results and 10 gave negative re-sults when injected into susceptible animals. The filters used in the nine posi-tive instances held back bacteria that were known to be present in the material before filtration, and at the same time al-lowed the infectious agent of the encep-halitis to pass. Other methods of identi-fication have so far failed entirely, where-as this method has given a strong promise of success. The work with infected chick embryos has been highly satisfactory and furnishes a cheap method of propagation whereby large amounts of infectious ma-terial can be obtained at frequent inter-vals. A study of the infected embryos and the different egg parts is continuing, but here again efforts to identify the causative agent by this study have so far failed. Bibliography 1. Cox, Harold R. 1938. Use of yolk sac of developing chick embryo as medium for growing Rickettsiae of Rocky Mountain spotted fever typhus groups. U. S. Pub. Health Rpts. 53:2241-2247 2. McNutt, S. H. 1940. A preliminary report on an infectious encephalomyelitis of cattle. Vet. Med. 35 :227 3. McNutt, S. H. 1940. Sporadic bovine encephal-omyelitis. Cornell Veterinarian 30:437-448 The Veterinary Student 

https://dr.lib.iastate.edu/bitstreams/753dda9e-d7a6-4f56-945b-fa773c3061bd/download

Bovine Encephalitis

Abstract

Similar works

Full text

Available Versions

Iowa State University Computer Science Technical Reports

Digital Repository @ Iowa State University (ISU)

Iowa State University Computer Science Technical Reports