MASSEY COLLEGE

Manawatu Standard, Volume LII, Issue 229, 27 August 1932, Page 4

MASSEY COLLEGE

LECTURES TO SHEEP BREEDERS. FOOT AND MOUTH DISEASE. PRESENT DAY KNOWLEDGE. , By .T. M. MeLinden, M.R.C.V.S., N.D.A. The spring of 1925 saw the comImencement of a bold policy of research into tho disoase known as Foot and Mouth Disoase. This was not tho first ■committee but actually tho third committee constituted to execute this policy. Breadth of Investigation. No limit. There was no hampering in any way of this committee which ■was given an absolutely free hand to investigate not only in Great Britain flrnt to extend their activities abroad. It was of paramount importance to Great Britain that this disease should be mastered if at all possible. Committee Members’ Qualifications. On that committee are to be found most distinguished veterinary and medical men from their corresponding institutions, every endeavour being made to bring together a very outstanding

group of scientists. Its representatives were all renowned for their scientific achievement. Facilities for Research. 1. Munst.rey's Laboratory, Weybridge. 2. Lister Institute for Preventive Medicines. There can be no question of the status of those two institutions and work done in either can be regarded as being as reliablo as it is humanly possible to be. 3. The National Institute for Medical Research. Their collaboration and help was always available. Experimental Station: It was found by a previous committee that this work could not bo satisfactorily carried on on an obsolete battleship, so the Ministry’s Cattle Testing Station at Pirbright was used. These buildings could be made to form a compound suitable for holding cattle, sheep and pigs, and also to have a buffer zone from which live stock could be excluded. Historical: Past Work. Recent Work of Immediate Interest. Much had been done before the institution of this committee, chiefly on the Continent of Europe, but it is the work of recent dato which concerns us. Chief Facts

Skeleton Symptoms: Briefly these are: —Stringy saliva flowing from tire mouth or jiossible lameness in one or more leet. A closer inspection would reveal watery blisters ot varying size upon the tongue, lips and checks and ulceration of the hoof head, the animals affected being cattle, sheep and pigs chiefly. Other animals and man are more rarely attacked. The disease is extraordinarily contagious to susceptible farm animals. It is the most contagious of all known diseases.

Cause: From tho first there was little doubt that it was caused by a living organism and one which was capable of rapid multiplication under suitable conditions.

Nature of Organism—Extraordinary. At one time this was the cause of much doubting but to-day it is known that it is not an ordinary organism capable of culture under ordinary laboratory methods—methods which have proved so successful in establishing the organism of many other infectious diseases. Inoculation Experiments—Blisters Infective : These experiments have repeatedly demonstrate that the virus of foot and mouth disease is present in the fluid of the vesicles on tho feet and mouth although under the microscope

no organism can he seen and although nothing can be grown from it. In recent years, many such examples, with other diseases, have been observed so that they are all gathered into a group which aro called ultra-visible viruses or filter passers.

Fact Observed in 1897 by Loffler and Frosch: It is as long ago as 1597 that Loffler and Frosch observed this peculiarity of t.ho vesicular fluid of foot and mouth disease. Tins finding has definitely been confirmed by the present investigating committee. An intense research lias since been going on by the leading veterinary and medical research workers of our time. Eroscli and Dabmen of Berlin believed that they had solved the difficulty of culture of this virus in 1924. That is culture in tho laboratory. They believed they had rendered it visible to photographic processes and this after 25 generations cultivating outsido tho body. Two main lines of investigation appeared essential, (a) the cultivation of the virus, and (b) n detailed study of tho disease as it affected rodents which had been artificially infected. Study of the Virus.

1. Attempted Cultivation Unsuccessful: The attempts made to grow the organisms from the vesicles of infected guinea pigs proved fruitless. Lest some inhibiting agency due to the vesicle fluid was at work, attempts were made to mechanically separate the virus. The work has been repeatedly done but 'there is no confirmation coming that Frosc-h and Dahmen’s methods will grow the vims. 2. Effect of Temperature: 30deg. C. rendered inocuous in 9 days—Loffler and Frosch; 37deg. C. undiluted vesicular fluid doad 12-21 hours; 37dcg. C., diluted vesicular survived 2-1 hours but not three days; 50deg. C, virus dead in 15 minutes. The effect of cold temperatures on the virus are very slight. ISdeg. C. virulent after 8 hours. In an ice chest, after 3 and 1 months, and in one instance afttr 8 months. At 4 deg. to 7 deg. C., virulent fluid from mouth is still active after 190 days. From tho feet at 4-4 cleg, to 3 deg. c., virulent fluid is still active after 124 days. The fluid was alternately frozen and thawed at least 20 times. At 55 deg. G. defibrinated blood infective at 15 minutes but not 20 minutes.

These facts are of importance with regard to the best method of disinfection of contaminated material: Action of Phenol: The Lister Institute showed that in .5 per cent, solution the virulence had not completely disappeared in 41 hours at 37deg. C. or 21 days at room temperature.

Action of Alcohol: The virus withstood (30 per cent, alcohol for IS hours at room temperature. Chlorine and lodine: Solutions containing free chlorine or iodine 1-100.000 and 1-50,000 respectively and potassium permanganate 1-50,000 were effective. Caustic soda was capable of disinfccing in 1-20,000 after three hours. These experiments repeated in fneces •reduced the efficacy of chlorine and iodine by one thousandth. Very weak solution of soda no longer sterilised, requiring 100 times as much.

Disinfection of Hay and Hides: This led to the disinfection of hay nnd (hides. It was found that grossly con-

taminated hay stacks could be effectively disinfected by spraying with a solution of formalin and apparently without destroying the hay. Hides soaked in 1 per cent, solution of formalin for 4S hours were disinfected. This is no use for hides. Distribution of Virus in the Body. It is evident that with the formation of the primary vesicle there is multiplication of the virus because when it is diluted one million fold it is infective.

From the primary vesicle tho virus soon reaches tho vossels and is distributed by the blood stream throughout the body. For two or three days after the appearance of the local lesion it can be recovered from the blood. Foot Lesions: Twenty-four hours after maturation of the primary vesicles secondary ve-siclos appear upon tho feet and tonguo. These two contain virus in high concentration. Disappearance of the Virus in Bodies of Living Animals: Vallee and Carre showed that infectivity of cattle rapidly declined after full development of the secondary vesicles. Although tho vesicles remained charged for several days with virus it was unusual for infection to spread from sick animals to healthy ones placed in contact with them.

Reppin recovered the virus occasionally as lato as 11 days after inoculation. He believes infectivity to have coased by the fourteenth day. It has been suggested that cattle may carry infection in or around the hoof after an attack of the disoaso, and may distribute it as the hoofs wear. YValdeman oxamined 63 but failed to find one after one or two months. Tho American Commission discovered one carrying the virus 34 days after infecti on.

In Germany the carcases of any cattle killed during convalosence are regarded as free from infection and used for food

These findings suggest that the high ly infective period of tho disease precedes tho eruption of the vesicles.

Natural Disinfection: Research makes it clear that there is a process of natural disinfection taking placo in tho living body. This begins immediately after tho vesicles on the feet and tongue have reached their maximum. This proceeds so quickly that infective material cannot be found about tho feet or mouth nor in the skin or tissues after one week. Exceptionally this does not happen however.

Survival of Virus Outside the Body: A low temperature nnd a dry atmosphere a.rc found to tie tho most favourable conditions for the survival of the virus. Light, particularly ultra-violet light has prejudicial action. Under natural atmospheric conditions t.he virus has not so far been found alive longer than five months.

AVhen dried on clean grass, cotton wool and filter paper, it dies rapidly. It has been found to live much longer upon hay arid bran. Diluted vesicle fluid was infective after 20 weeks. On cow hair it was infective after one month.

After wot and dry salting virus recovered after 42 days from the bone marrow, the disease being readily conveyed to pigs by feeding the crushed bones.

Source of Infection: These experiments help to oxplain the ways in which infection may lie dormant for months and then give rise to further outbreaks. It appears that the virus in carcases or driod discharges upon foddor and hah - is perhaps of greater significance than is carriage in the bodies of recovered animals.

Plurality of Types: Vallee and Carre showed that there were two types, but the German Commission showed later that it was more complicated still, for they eliminated a third type. This complicates preventive treatment as it will bo necessary to ascertain to what type the outbreak belongs if these measures are to have a reasonable chance. Dr. Cinoa of Bucharest, appears to have solved the identification process. Susceptibility of Wild Animals.

As many outbreaks were of undiscovernblo origin, wmrk was started to investigate tho possible part played by wild animal life.

Rodents other than guinea pigs and rabbits were found to possess a natural resistance to foot and mouth disease and e\on when they could be infected the disease did not spread by natural means. Wild rodents did not seem to plav a part in the spread of the disease. W'iid rabbits infected with virus did not infect their cage mates. A rat was found in the Ministry’s researoh station suffering from foot and mouth disease and one other was found on a farm where an outbreak occurred. Immunity. An animal which has had an attack of foot and mouth disease is resistant to inoculations for from six months to one year. The belief that immunity is short lived has been explained by the discovery of three typns which cannot bo distinguished clinicalry and which do not protect one against the other. Questions Mr. Wheeler: What in your opinion are the chances of this disease ('hfot and mouth) being introduced by stoCKcoming from Great Britain? Prof. Peren: I regret to say that the college cannot be drawn into tho controversy on this matter. A member of tho audience: You state that this disease does not often prove fatal; would you please tell us how it afreets an animal?

Mr. MclAnden: The disease does not prove fatal, but one cannot ignore the economic effect. Stock which have been affected, but which have recovered, are, under the very best of treatment and management, extremely poor producers, either as milkers or fatteners, for a number of years in some cases, but in all cases for at least ono year. Then again, in-calf cows almost always lose their calves, and from the stud breeder’s point of view this would be his greatest loss, for such calves are always born dead. Mr. J. A. Mitchell: In 1920 I was in South America and visited a farm which had 50 cows suffering from foot and mouth disease. 1 can tell vou that the animals which had had the disease were physical wrecks in every way, and of course the calves dio. Mr. Hewitt: You tell us that there are no virus carriers. Two years ago at an agricultural conference held in Wellington it was stated by one of those present that he had received iot-

tors from a veterinarian, in the United States of America to the effect that there might be virus carriers of this disease. If this is the caso it is too dangerous to open our doors, but if it is not so, I withdraw my opposition. Mr. McLindcn: Tho American commission investigating foot and mouth disease does not state that there are virus carriers, and one can take it that these gentlemen would say so if they even suspected carriers to exist.