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This article was published in 1940
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
SOME RESULTS OF RECENT RESEARCH AT GLENFIELD VETERINARY RESEARCH STATION
By W. L. HINDMARSH, B.V.Sc., M.R.C.V.S., D.V.H.,
Director of Veterinary Research.
The results of investigations into stock diseases are usually not available until the work is complete and ready for publication although it is the custom to circulate to field officers information that may be suitable for immediate application. Some comments on the work in progress will therefore be of interest to inspectors and of use to them in the pursuance of their duties.
SALMONELLA INFECTIONS.
The Salmonella group of bacteria is closely related to the Typhoid bacillus and it has been a common custom to refer to these organisms as Paratyphoid bacilli. These are not only capable of causing ill-health in man and animals by direct infection, but they are the most common cause of food poisoning when they have infected milk, meat, sausages, pies, icecream and other foodstuffs. In European countries they have come into prominence of recent years because duck eggs infected with Salmonellae have been reported to have caused food poisoning in human beings who ate the eggs. In Australia we have recognised for a long time that one species of Salmonella was the cause of ill-health in pigs. In acute cases it caused septicaemia with heavy mortality but in less virulent infections it caused Necrotic Enteritis, a disease scheduled under the Stock Diseases Act. It is, however, only in recent years that Salmonellae have been incriminated as a cause of sheep mortality in Australia. In the first outbreak attributed to this infection, some hundreds of sheep had died. The organism was recovered from a waterhole in one of the paddocks and there is little doubt that the disease was water borne. The sheep showed a high fever, diarrhoea and later dysentery. On post-mortem examination there was intense gastro-enteritis frequently with free haemorrhage. Swelling of the spleen was also present and this lesion is a useful guide in conjunction with the inflammatory changes of the digestive tract; Of course, other internal organs such as the mesenteric lymphatic glands, liver and kidney show swelling and congestion and petechiation of the serous membranes may be noted. This is the classical picture but, as in all diseases, every case does not run true to form and a reference to Mr. Walker's article in your year book for 1939 will give much valuable information on the field investigation, and the post-mortem findings as seen by him. These cases were not altogether typical.
BRUCELLA INFECTION OF PIGS (Infectious abortion).
This disease is related to Contagious Abortion (Bang's Disease of cows) but the organism, although indistinguishable from that of the cattle infection except by special tests, is more virulent to the human being. In America it is a recognised hazard of the pig slaughtering industry and the majority of cases of Undulant Fever in that country have been derived from infected pigs. Infectious Abortion of pigs has recently come into prominence by reason of the fact that the disease has been found in a few piggeries. In one, the majority of the pigs tested was found infected. It was felt that the position demanded immediate action and arrangements have been made for a survey of the pig raising districts. In other countries it has been found that the boar is the chief agent of spread. The bacilli picked up, usually by service of an infected sow, invade the genital tract and its associated glands, and are passed out with the semen in service. It also is passed out in the urine. Infection can also be effected by ingestion and by the skin. Whilst in America the disease has been regarded as a self limiting one, that is to say after the first outbreak the disease lessens in intensity naturally, in other countries it has been looked upon more seriously and rigid methods of control have been adopted. There is evidence now that veterinarians in America have changed their attitude especially since the discovery that the infecting organism is pathogenic to man. The bacillus is apparently more resistant to exposure than the cattle strain and some American authorities consider it unsafe to place uninfected pigs in yards previously used for infected animals under a period of two years. In addition to abortion this infection may cause birth of dead pigs, metritis and sterility. As in the case of cattle, infected pigs can be selected by the agglutination test.
ARTHRITIS IN LAMBS.
Although we know the cause of this disease and have found that the infection gains entrance from skin wounds, especially at marking time, we have had reports of severe outbreaks in young lambs that had not been marked. It, was evident that all these lambs could not have received injuries and experiments have been commenced to ascertain if there are other methods of infection. At Glenfield three recently born lambs became infected after a small quantity of culture had been applied to their feet and it is evident from this that in very young lambs infection can pass through the intact skin. This offers an explanation of the field experiences. Further work is in progress. In addition, experiments are being conducted to ascertain if any method of immunising lambs can be evolved.
VITAMINS AND FERTILITY.
It is evident that we are now on the threshhold of many discoveries regarding the part played by those accessory food substances known as vitamins. One of these is known as the Anti Sterility factor or Vitamin E. It is marketed commercially in the form of wheat germ oil which is rich in this vitamin. Many extraordinary claims have been made for this substance but until further research is conducted one must be hesitant about accepting them. Most of the experiment work had been carried out with rats, and results that are obtained in rat experiments are not necessarily applicable to larger animals. It is generally accepted that a lack of Vitamin E will lead to sterility in both male and female animals. Since our live stock are fed largely on natural foods it is probable that under ordinary conditions they do not suffer from any lack of it. Avitaminosis E in rats leads to degeneration of the testes in the male and abnormalities of the foetus leading to resorption or death in the female. Claims have been made that the administration of Vitamin E protects against Bang's Disease but these have not been substantiated and are not generally accepted. The following case is reported as being of interest:—
A local farmer reported that a Berkshire boar, purchased by him, showed no sexual desire whatever. It grazed with sows and took no interest whatever when the sows were in oestrum. He was inspected by us and was well grown but rather effeminate in appearance. The testes appeared normal. Wheat germ oil was prescribed to be given twice weekly. After the fourth dose his disposition changed and the hitherto quiet lazy animal resented handling. He became more masculine in appearance. When allowed to graze with sows he attempted to mate with them although they were not in oestrum. In all, he received six doses of oil each of 5 ml. About six weeks after the commencement of the treatment he served a sow and since he has mated with a number of others. The sows are apparently impregnated and we are waiting the parturitions.
This boar was mature, had been on the farm five months without evincing any sexual desire and the owner had decided to castrate it, when he first mentioned it to us. There seems little doubt that the altered sexual behaviour of this animal was due to the wheat germ oil.
AVIAN ENCEPHALOMYELITIS.
This is a nerve infection of poultry recently recognised for the first time in Australia. The disease was first reported upon in America in 1932 under the name of "Epidemic Tremor." Later work revealed that it was a specific infection due to a virus. Mortality in some hatcheries in America was reported to be high. Last year, chicks showing symptoms similar to those described in U.S.A. were submitted to this Station for examination, and, during the succeeding eight weeks, birds from eight outbreaks were received. There is no doubt that the disease investigated by us was identical with that occurring in America. The chief symptom is progressive inco-ordination of muscular action until finally the chicks are unable to stand. In the early stages the birds are dull, and sit about instead of moving actively. Death may occur quickly but usually the chicks die of starvation because they cannot move to their food and water. Many of the chicks develop a muscular tremor which is characteristic; it affects the head and neck chiefly, and may be so fine and rapid that it is difficult to perceive with the eye but is readily detected when holding the bird. The virus attacks the brain and although this may appear normal to naked eye examination typical lesions are seen in microscopic preparations. The method of spread is not yet known but there are indications that it may be transmitted through the egg. No method of control is at present known.
SWINE DYSENTERY.
This is a disease which will be confused with Necrotic Enteritis (Swine Paratyphoid). It has been recognised as a separate entity in N.S.W. during the past three years. The chief lesion is necrosis of the mucous membrane and subcutaneous tissue of the colon. The following differential features are therefore of interest.
Age incidence. In N.S.W., Swine Dysentery has been seen mostly in pigs over four months of age although younger pigs are affected. Necrotic enteritis usually attacks younger pigs.
Temperature. In Swine Dysentery the temperature is usually very high up to 108°. In Necrotic Enteritis it rarely passes 106°.
Appetite is completely suppressed in Swine Dysentery. Appetite may be impaired in Necrotic Enteritis but is usually not absent except in septicaemic cases.
Faeces. In Swine Dysentery faeces are fluid, contain much blood and later contain many shreds of necrotic mucous membrane that have been shed. In Necrotic Enteritis there is diarrhoea but, no dysentery. Faeces are usually foetid.
Course. The course of Swine Dysentery is short. The disease ends with recovery or death within seven days of the exhibition of symptoms. In Necrotic Enteritis the course is more chronic, the period between the first sign of illness and death depending upon the virulence of the infecting organisms.
Lesions. In Swine Dysentery the characteristic lesions are confined to the colon and the caecum. They appear to commence in the colon and the caecum is involved only at a later stage. The condition commences with oedema and swelling continuing to extensive necrosis of the mucous membrane. A feature of value is the clearly cut limitation of the lesions to the large bowel, the small bowel is not affected. In Necrotic Enteritis the lesions commence as separate ulcers covered with necrotic tissue. These are frequently close to the ileo caecal valve. The caecum is involved early in the disease. Later, the ulcers may coalesce and the greater portion of the bowel mucous membrane becomes affected, so that the appearance is very similar to Swine Dysentery. The small bowel, however, usually congested and may also be ulcerated whilst gastric congestion and serious involvement of spleen, liver and kidney are common.
The cause has not been determined. There is evidence that rigid disinfection of affected sties will assist in the control. The administration of yeast appeared to have some beneficial effect as a preventive.