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On Tracing the Source of Tuberculous Milk
THE SOURCE OF TUBERCULOUS MILK
495
The working expenses have been estimated a t kr. 46 ,goo , b ut owing to rise in prices this amount must now proba bly be doubl ed. The receipts have been estimated at kr. 25,500, which can hardly be increased.
ON TRACING THE SOURCE OF TUBERCULOUS MILK. By H. T. MATTHEWS. B.V.Sc. D.V.H., F.R.C.V.S., Veterinary Department, C1:ty of Liverpool.
TH E task o i discovering and dealing with th e origin of tuberc ulous milk was, until recentl y, performed mainly by veterinary surgeons a ppointed by th e town s in which such milk was being consumed . Since the change in legisla ti on which delegated th e responsibility to the Authority of the producing districts , m any practitioners have had to tackle what was to them a n unknown problem , with th e natural result that standards of action a nd of effi ciency vary markedly in different districts , even in the same county. In law it is the province of th e medical offi cers of health to define the course of the investiga ~ tion , but in practice th ey seem content to leave it to the veterinary s urgeon . The ob ject of this a rticl e is to discuss the scope of such veterin a ry inquiry a nd to name some of the difficulties which arise . The greate r number of these cases occur as a result of a bulk sa mple having bee n t,a ken in th e consuming district , usually a town. It is h elpful to h ave some knowledge of the ma nner in which such samples a re obtained for t est. Ordinarily the sampling is done by a sanitary in spector at the destination of the milk , or it may be before actual a rrival at the premises of the milk dealer , for example , at a railway station. In either case he is faced with a row of cans of ma ny shapes a nd sizes, marked in a diversity of ways, coming from numerous d istricts. He has no infallibl e means of knowing what his sample invol ves. It m ay be from only half a dozen cows of a big herd , o r it may represent t he whole herd or many h erds. Unless the can is sealed he cannot t ell wh eth er it is as it st arted from the farm or has been subj ected to contam ina tion en ro ute. Statements as to its origin made, possibly in good fai th , by the milk d eale r, but in the absence of a da ted sealed lab el, a re of questionable value . P erhaps the can has neve r been sterilized in its life , a nd contains bact eri a acquired many days before. And so on . After all , Ostertag showed th a t it was t heoretically possible for the product of one tuberculous udder to be diluted with more tha n a whole day's supply for the entire country, and s till infec t a guinea-pig. So long as we recognise th e possible
496
THE VETERINARY JOURNAL
a nd , indeed , inevita ble, errors of the bad sys tem of bulk-samp ling , we shall be better occupied in doing our pa rt of the work properly, tha n in bla ming others for a nomalies tha t a rise. Even guinea-pigs have been known to disagree a mong themselves as to . th e correc t result of a sample. The medical offi cer of the producing district must ta ke, a t its face value, the statement , by the medical offi cer of the consuming district , th a t a sample of milk taken on such a da te, coming from such a fa rm , proved tuberculous. It may be the truth . It is a n incomplete statement at bPst , a nd always la te, in that there has been plenty of time for damage . If correct; in mos t cases it ought to be possible to trace the source of the infection , but not in all . Some ve terina ry surgeons will begin the investigation by a clinical examina tion of the suspected cattle, ha ving in mind only the fac.t that they a re suspec t. Others will like to interrogate the farmer firs t . P ersonally, I prefer the former method as giving more freedom for unbiased judgment. The examina tion can properly be conducted a t any time between morning milking a nd about noon, or after evening milking . Very few cows fill up with milk before noon so as seriously to interfere with palpa tion . It is important to h a ve all the milking stock on the fa~:m submitted , whether dry or not. There is a distin ct advantage in being present during milking so as to see the sta ndard of method employed. While the examination is primarily directed towards th e udders, a general view of each cow is desira ble, a nd indeed is una voidable. Condition , respira tion and the wall in front , a re the ma in points, in addition to palpa tion of each quarter and teat. The eyes should certainly. assist the fmgers in examination of the udder , and especially of the teats.. The greater the skill , the greate r the speed , up to a point. If a case of tuberculous mas titis is found , p robably the source of the original infection has been discovered , but it is not neces a rily" the only source. A sample of milk from the infected qua rter, or qua rters, is ta ken, direct into a sterile bottle, for subsequent confirmatory examination . It matters little whether it be fore-milk , middle or strippings. Bacteriologis ts like to have about six ounces for biological test . One ounce is enough for microscopic diagn osis. The remainder of the herd should certainly be controlled in one or more group samples, to make sure tha t no other early case has been missed. But it is when no such definite culprit is de tected tha t diffi culty arises. Probably some degree of suspicion ·will be directed to on e or m ore of the cow . H ere the element of individual judgment enters
THE SOURCE OF TUBERC1JLOUS MILK
497
and mus t determin e whe ther th ey a re to be sampled ·separately , a nd if their milk is to be withdra wn from the supply. While approximate standardisation of system is both possible a nd desirable, it is not possible to sta ndardise cl inical skill. If there is reasonable doub t , the consumer must be co nsidered fir t , but it is my experi ence that prac titioners a re inclin ed to e rr 0 11 the side of severity, and th at many a cow's milk is stopped without due ca use. Not infrequently it ha ppens th at no cow can Le singled out as the likely source of th e trouble. In view of the numerous possibilities of infection other th a n direc t from a cow, one is tempted to declare the h erd clini ca lly health y and leave it at that. I a m sure tha t such lack of decisive conclusion is wrong. In prac tically every case wher e a bulk sam ple has been found tuberculous, the suspected herd should be put to furth er test by control (o r group) samples. Such sa mp l e~ are a lways taken in the confident hope that th ey will· be returned _n egative, a nd so free the herd from suspicion . ·Sometimes, of coyrse, the hope is '!ot realised, in which case one has at .least n armw~ d~.~ h ~ .field , of later _inquiry. The guinea-pig , with all his _faults, is m or~ sensitive than is the mos t delicate clinical touch , and the be~ t mao "will have disappointments a t times. One or two streams of · milk from each teat of each cow, form. sufficient material for a control sample. If taken into a jug from the fa rm kitchen, it should be remembered that the jug has proba bly held milk before, and that washing is not sterilization . How ma ny cows to include in one sample is a question th a t can only be determined by the particula r circum sta nces of the case. It depends on the clinical findings, on the clinician 's confidence in hi s judgment , on the size of the herd , the arrangement of cowsh eds and so on. Probabl y it is seldom desirable to control more than 20 in one group. Interrogation of the farme r is an essential pa rt o f the in vestigation. What cows have been sold off since the original sample was taken ? \ Vhy ? . nless some special reason exists, it is hyper-effi cient to trace these to their destina tion . Have any died ? H ow many have gone dry , and how many calved ? And , particula rly as the fa rmer has had notice of the pending examination , what is in the loose-box in the stack-yard , or out in the pas ture farth est from the road ? Delicate q uestions, these. D oes an y n eighbour's milk go in with his? Does anybody else use his cooler ? Does he ge t his own cans back regularly? Are they ever , to his knowledge, sterilized ? Possible causes of the original infection , but difficult of proof, a re numerous. F cecal contamin ation . from dirty cows in dark cowsheds, is probably a fruitful source, in view o f the enormous incidence of the disease among da iry herds. Mud dropped into the milk is likely to have
THE VETERINARY JOURNAL
498
been derived from a picturesque pond , into which all the tuberculous cattle of the farm have def
I9IS.
M.O.H .
FARM. .. . ...... . .. .. .. . ... .... . . .... .... . ... . ... . .. ........
M IL EAGE ...... . .. .. ... .
DATE OF V I SIT ........ ....... . . ..... . . BuLK SAMPLE TAKEN AT ... ...... ... o N ............ R ETURNED PRESENT MILKIN G H ERD CHANGES ... CLINI C AL NOTES AI\D . SAMPLE S TAKEN
T.B ... ...... .. . .
39 in milk, 4 dry. All examined. 2 sold beef, I gone dry , 2 calved , purchased.
I
newly
The herd consists mainly of young cattle ·i n fair condition. Sample No . 1. Aged red cow , white fa ce, cock horns , standing seccmd from door of long shed. L.H. quarter enlarged, indurated. Nohistory. Micro. positive.
SECTION OF COMPARATIVE MEDICINE Sample N o.
Control. 16 in long shed (excluding red cow and 2 dry) . Control. I I on house side· of double shed. Control. 10 on far side of double shed (excluding z dry and blue poll cow with acute mastitis) .
2.
N o. 3· No . 4·
REMARKS
499'
I am dealing with the red cow (S ample 1) under the T.B. Order forthwith. The milk of the blue poll cow is withdrawn pending recovery. Samples 2, 3 and 4 are submitted f or· guinea-pig test. The cattle are dirty. Signed ............ .. ........... . .. .. .... . ... ... . .... . ....... R.C.V .S.
SECTION OF COMPARATIVE MEDICINE. President- Sir
D ' AR CY
PowER, K.B.E. , F .R. C.S.
(March 28th, 1928.)
Intradermic Tuberculin Testing in Cattle.*
By T. DALLING, j. H. MASON
and
W. S. GORDON.
Proceedings of the Royal Society of Medicine, July, 1928. WE have carried out many tests in cattle, using concentrated tuberculiru intradermically, and some of the points investigated have already b een published. Two herds of milch cows have been under our observa tion for the past three years, and , using the double intradermic tuberculin test t wice a year, we ha ve succeeded in separating react ors from non-reactors· and in keeping the non-reactor sections tubercle free. F arm A had 103. milk cows and heifers, and when tested in 1925 , 67 reacted positively a nd 36 gave a negative result . From the non-reacting cows 6 were chosen for the supplying of milk for calf-rearing and removed to a special calf-rearing farm ; 31 of the best cows were removed to a new farm , These cattle have been tested twice annually for the last • R eprinte d b y permi ssion of the E ditor of th e proceed in gs o f t h e R oyal. Societ y o f Me dicin e.
495
The working expenses have been estimated a t kr. 46 ,goo , b ut owing to rise in prices this amount must now proba bly be doubl ed. The receipts have been estimated at kr. 25,500, which can hardly be increased.
ON TRACING THE SOURCE OF TUBERCULOUS MILK. By H. T. MATTHEWS. B.V.Sc. D.V.H., F.R.C.V.S., Veterinary Department, C1:ty of Liverpool.
TH E task o i discovering and dealing with th e origin of tuberc ulous milk was, until recentl y, performed mainly by veterinary surgeons a ppointed by th e town s in which such milk was being consumed . Since the change in legisla ti on which delegated th e responsibility to the Authority of the producing districts , m any practitioners have had to tackle what was to them a n unknown problem , with th e natural result that standards of action a nd of effi ciency vary markedly in different districts , even in the same county. In law it is the province of th e medical offi cers of health to define the course of the investiga ~ tion , but in practice th ey seem content to leave it to the veterinary s urgeon . The ob ject of this a rticl e is to discuss the scope of such veterin a ry inquiry a nd to name some of the difficulties which arise . The greate r number of these cases occur as a result of a bulk sa mple having bee n t,a ken in th e consuming district , usually a town. It is h elpful to h ave some knowledge of the ma nner in which such samples a re obtained for t est. Ordinarily the sampling is done by a sanitary in spector at the destination of the milk , or it may be before actual a rrival at the premises of the milk dealer , for example , at a railway station. In either case he is faced with a row of cans of ma ny shapes a nd sizes, marked in a diversity of ways, coming from numerous d istricts. He has no infallibl e means of knowing what his sample invol ves. It m ay be from only half a dozen cows of a big herd , o r it may represent t he whole herd or many h erds. Unless the can is sealed he cannot t ell wh eth er it is as it st arted from the farm or has been subj ected to contam ina tion en ro ute. Statements as to its origin made, possibly in good fai th , by the milk d eale r, but in the absence of a da ted sealed lab el, a re of questionable value . P erhaps the can has neve r been sterilized in its life , a nd contains bact eri a acquired many days before. And so on . After all , Ostertag showed th a t it was t heoretically possible for the product of one tuberculous udder to be diluted with more tha n a whole day's supply for the entire country, and s till infec t a guinea-pig. So long as we recognise th e possible
496
THE VETERINARY JOURNAL
a nd , indeed , inevita ble, errors of the bad sys tem of bulk-samp ling , we shall be better occupied in doing our pa rt of the work properly, tha n in bla ming others for a nomalies tha t a rise. Even guinea-pigs have been known to disagree a mong themselves as to . th e correc t result of a sample. The medical offi cer of the producing district must ta ke, a t its face value, the statement , by the medical offi cer of the consuming district , th a t a sample of milk taken on such a da te, coming from such a fa rm , proved tuberculous. It may be the truth . It is a n incomplete statement at bPst , a nd always la te, in that there has been plenty of time for damage . If correct; in mos t cases it ought to be possible to trace the source of the infection , but not in all . Some ve terina ry surgeons will begin the investigation by a clinical examina tion of the suspected cattle, ha ving in mind only the fac.t that they a re suspec t. Others will like to interrogate the farmer firs t . P ersonally, I prefer the former method as giving more freedom for unbiased judgment. The examina tion can properly be conducted a t any time between morning milking a nd about noon, or after evening milking . Very few cows fill up with milk before noon so as seriously to interfere with palpa tion . It is important to h a ve all the milking stock on the fa~:m submitted , whether dry or not. There is a distin ct advantage in being present during milking so as to see the sta ndard of method employed. While the examination is primarily directed towards th e udders, a general view of each cow is desira ble, a nd indeed is una voidable. Condition , respira tion and the wall in front , a re the ma in points, in addition to palpa tion of each quarter and teat. The eyes should certainly. assist the fmgers in examination of the udder , and especially of the teats.. The greater the skill , the greate r the speed , up to a point. If a case of tuberculous mas titis is found , p robably the source of the original infection has been discovered , but it is not neces a rily" the only source. A sample of milk from the infected qua rter, or qua rters, is ta ken, direct into a sterile bottle, for subsequent confirmatory examination . It matters little whether it be fore-milk , middle or strippings. Bacteriologis ts like to have about six ounces for biological test . One ounce is enough for microscopic diagn osis. The remainder of the herd should certainly be controlled in one or more group samples, to make sure tha t no other early case has been missed. But it is when no such definite culprit is de tected tha t diffi culty arises. Probably some degree of suspicion ·will be directed to on e or m ore of the cow . H ere the element of individual judgment enters
THE SOURCE OF TUBERC1JLOUS MILK
497
and mus t determin e whe ther th ey a re to be sampled ·separately , a nd if their milk is to be withdra wn from the supply. While approximate standardisation of system is both possible a nd desirable, it is not possible to sta ndardise cl inical skill. If there is reasonable doub t , the consumer must be co nsidered fir t , but it is my experi ence that prac titioners a re inclin ed to e rr 0 11 the side of severity, and th at many a cow's milk is stopped without due ca use. Not infrequently it ha ppens th at no cow can Le singled out as the likely source of th e trouble. In view of the numerous possibilities of infection other th a n direc t from a cow, one is tempted to declare the h erd clini ca lly health y and leave it at that. I a m sure tha t such lack of decisive conclusion is wrong. In prac tically every case wher e a bulk sam ple has been found tuberculous, the suspected herd should be put to furth er test by control (o r group) samples. Such sa mp l e~ are a lways taken in the confident hope that th ey will· be returned _n egative, a nd so free the herd from suspicion . ·Sometimes, of coyrse, the hope is '!ot realised, in which case one has at .least n armw~ d~.~ h ~ .field , of later _inquiry. The guinea-pig , with all his _faults, is m or~ sensitive than is the mos t delicate clinical touch , and the be~ t mao "will have disappointments a t times. One or two streams of · milk from each teat of each cow, form. sufficient material for a control sample. If taken into a jug from the fa rm kitchen, it should be remembered that the jug has proba bly held milk before, and that washing is not sterilization . How ma ny cows to include in one sample is a question th a t can only be determined by the particula r circum sta nces of the case. It depends on the clinical findings, on the clinician 's confidence in hi s judgment , on the size of the herd , the arrangement of cowsh eds and so on. Probabl y it is seldom desirable to control more than 20 in one group. Interrogation of the farme r is an essential pa rt o f the in vestigation. What cows have been sold off since the original sample was taken ? \ Vhy ? . nless some special reason exists, it is hyper-effi cient to trace these to their destina tion . Have any died ? H ow many have gone dry , and how many calved ? And , particula rly as the fa rmer has had notice of the pending examination , what is in the loose-box in the stack-yard , or out in the pas ture farth est from the road ? Delicate q uestions, these. D oes an y n eighbour's milk go in with his? Does anybody else use his cooler ? Does he ge t his own cans back regularly? Are they ever , to his knowledge, sterilized ? Possible causes of the original infection , but difficult of proof, a re numerous. F cecal contamin ation . from dirty cows in dark cowsheds, is probably a fruitful source, in view o f the enormous incidence of the disease among da iry herds. Mud dropped into the milk is likely to have
THE VETERINARY JOURNAL
498
been derived from a picturesque pond , into which all the tuberculous cattle of the farm have def
I9IS.
M.O.H .
FARM. .. . ...... . .. .. .. . ... .... . . .... .... . ... . ... . .. ........
M IL EAGE ...... . .. .. ... .
DATE OF V I SIT ........ ....... . . ..... . . BuLK SAMPLE TAKEN AT ... ...... ... o N ............ R ETURNED PRESENT MILKIN G H ERD CHANGES ... CLINI C AL NOTES AI\D . SAMPLE S TAKEN
T.B ... ...... .. . .
39 in milk, 4 dry. All examined. 2 sold beef, I gone dry , 2 calved , purchased.
I
newly
The herd consists mainly of young cattle ·i n fair condition. Sample No . 1. Aged red cow , white fa ce, cock horns , standing seccmd from door of long shed. L.H. quarter enlarged, indurated. Nohistory. Micro. positive.
SECTION OF COMPARATIVE MEDICINE Sample N o.
Control. 16 in long shed (excluding red cow and 2 dry) . Control. I I on house side· of double shed. Control. 10 on far side of double shed (excluding z dry and blue poll cow with acute mastitis) .
2.
N o. 3· No . 4·
REMARKS
499'
I am dealing with the red cow (S ample 1) under the T.B. Order forthwith. The milk of the blue poll cow is withdrawn pending recovery. Samples 2, 3 and 4 are submitted f or· guinea-pig test. The cattle are dirty. Signed ............ .. ........... . .. .. .... . ... ... . .... . ....... R.C.V .S.
SECTION OF COMPARATIVE MEDICINE. President- Sir
D ' AR CY
PowER, K.B.E. , F .R. C.S.
(March 28th, 1928.)
Intradermic Tuberculin Testing in Cattle.*
By T. DALLING, j. H. MASON
and
W. S. GORDON.
Proceedings of the Royal Society of Medicine, July, 1928. WE have carried out many tests in cattle, using concentrated tuberculiru intradermically, and some of the points investigated have already b een published. Two herds of milch cows have been under our observa tion for the past three years, and , using the double intradermic tuberculin test t wice a year, we ha ve succeeded in separating react ors from non-reactors· and in keeping the non-reactor sections tubercle free. F arm A had 103. milk cows and heifers, and when tested in 1925 , 67 reacted positively a nd 36 gave a negative result . From the non-reacting cows 6 were chosen for the supplying of milk for calf-rearing and removed to a special calf-rearing farm ; 31 of the best cows were removed to a new farm , These cattle have been tested twice annually for the last • R eprinte d b y permi ssion of the E ditor of th e proceed in gs o f t h e R oyal. Societ y o f Me dicin e.