herd tests on meat livestock to protect consumers from zoonotic pathogens and chemical residues
TRANSCRIPT
Veterinary Science Communications, 2 (1978) 63--72 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands �9 ECSC, EEC, EAEC, Luxembourg, 1978
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EUROPEAN COMMUNITY PREVIEW ARTICLE
HERD TESTS ON MEAT LIVESTOCK TO PROTECT CONSUMERS FROM ZOONOTIC PATHOGENS AND CHEMICAL RESIDUES
D. GROSSKLAUS
Federal Health Department, Institute of Veterinary Medicine, (Robert von Ostertag Institute), Berlin, Dahlem, (Federal Republic of Germany)
ABSTRACT
Grossklaus, D., 1978. Herd tests on meat livestock to protect consumers from zoonotic pathogens and chemical residues. Vet. Sci. Commun., 2: 63-72.
Clinical veterinary work is of prime importance for the task of the veterinary food hygienist. This is particularly true of early clinical, allergological, serological and bacteriological examination of herds of meat livestock, as proposed by Bartels, Kampelmacher, Grossklaus and others. Such investigations would make it possible to diagnose latent types of zoonosis which would otherwise remain undetected during official meat inspection. The pathological and anatomical findingsduring meat inspection are also of clinical importance. To these must be added the necessary measures to eliminate toxicologically significant residues of pharmacologically active substances. On ~he basis of his own research the author presentsproposals for herd tests which could help to promote, with improved safety, international trade in animal products for human consumption.
INTRODUCTION
The changing disease situation among meat livestock in many
countries, the trend towards factory farming and the continued
extension of international trade in animals and animal foodstuffs
mean that food hygienists must examine new ways of developing trade
and protecting consumers against pathogens and harmful chdmical
residues. One way of doing this under existing national and
supranational meat hygiene regulations is to carry out regular
examinations of slaughtered animals at source, as discussed by
* This article was originally written in German. Copies of the German version maybe obtained free of charge by writinq to: Mr. j. Rodesch, Corimission of the European Communities, DG XIII, B~timent Jean Monnet, Rue Alcide de Gasperi, Kirchberg, Luxembourg.
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Bartels (1963, 1966), Dutschke (1966), Grossklaus (1968),
Kampelmacher (1969) and others. There &re two purely technical
reasons for carrying out herd tests.
i. Many animals are carriers of zoonotic pathogens but have at
the time of slaughter no clinical signs of disease. During
examinations of the living animal and the meat, it is not as
a rule possible to identify such animals. This loop-hole in
the system of official meat inspection may have adverse effects
on consumers.
2. The inspection of slaughtered animals for harmful residues of
chemical substances in meat and organs is pointless unless it
is possible to check on the situation in the herd of origin
when results are positive. Early random sampling of the
environment, feed and excreta (urine and faeces) of the animals,
however, could reduce the risk of undesirable contamination
in the meat produced. Finally, advice to the owner Of the
animals and supervision of the use of drugs on and in the
animal would ensure that 'waiting periods' are observed before
slaughter.
Figure 1 shows the most important zoonotic pathogens which often
remain undetected in slaughtered animals at the official meat
inspection as a result of latent infection and the absence of
pathologic anatomical changes in the organs. The list is based
mainly on the situation in the Federal Republic of Germany where
cattle and pig stocks are free of tuberculosis and brucellosis:
Infectio~s diseases
Tuberculosis
Brucellosis
Salmonellosis
Listeriosis
Leptospirosis
Toxoplasmosis
Rickettsiosis
Trichinosis
Incidence
Cattle, pigs, poultry
Cattle, pigs, sheep and goats
Cattle, pigs, sheep and goats, poultry
Cattle, sheep, goats, pigs, poultry
Pigst cattle, sheep
Pigs, poultry
Cattle, sheep, goats
Pigs
Cysticercosis (G. inermis) Cattle
Fig. 1. Types Qf zoonosis relevant to meat hygiene. Note underlining indicates those animals for which herd tests to determine the infected state are desirable.
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Figure 2 reviews the source of various residues in a, nimal foodstuffs:
Additives to feedstuffs
Drugs > A n i m a 1
Eggs
Pesticides
//Substances from
r contaminated
environment
Milk
Meat
Fig. 2. Origin of various residues in animal products for human consumption.
It is certain that most residues come from drugs which are
legally or, unfortunately, illegally administered. There are three
main reasons for the use of drugs by laymen without veterinary
precription:
a. diseases of iyoung animals
b. mastitis
c. growth promotion
During the past three years concern about the residues of
pharmacologically active substances has led legislators in the
Federal Republic of Germany to amend a number of laws or to
pass new ones. Laws on foodstuffs, drugs and animal feeding
stuffs have thus been improved and certain chemical substances
are now not permitted as residues in foodstuffs while maximum
levels have been set for others, (acceptable levels). The central
idea of these statutory provisions is the introduction of waiting
periods, viz. the time during which residues of harmful substances
may be expected in feedstuffs obtained from animals treated with
drugs in accordance with regulations. Until a waiting period has
been determined from detailed tests on the elimination rates of
the particular chemical substance a transitional ruling requires
a five day delay. FortuNately similar drug and feedstuffs laws are
being considered for all European Community countries with the
result that no one competitor wiil have an unfair advantage.
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Methods of identifying zoon0tic pathogens and residues in the source stock
The veterinary surgeon treating farm animals will in future have
an important part ~ to play in the hygienic production of animal
foodstuffs. He will increasingly be concerned not only with
maintaining the health of the animals in his care but also with
guaranteeing the quality of foodstuffs obtained from the animals.
In our opinion, he can do this by means of regular stock tests if
research helps him by providing practical methods for reliable
detection of pathogens and residues in the living animal. In
addition, the clinical veterinary surgeon knows the health conditions
of the animal stocks and can prevent inappropriate or even illegal
use of drugs. Close contact with the owner of the animals also
helps him to ensure the observance of waiting periods and to
provide only animal drugs which do not result in harmful residues.
For example Figure 3 demonstrates contamination pathways following
------- Insecticide
Insects on the animal
(Lice, fleas, mites, flies)
Insects in animal housing Contamination of
(air, walls, floor) feed
Animal bodies~ ~'~
Animal products for human consumption
Fig. 3. Uptake of insecticides by animals
the incosrect use of insecticides, which are mostly chlorinated
hydrocarbon derivates. In this case it is clear that only the
clinician can eliminate the causes and demonstrate the effects.
It also shows the close links between clinical and veterinary
food hygiene work and how both equally serve the consumer.
Since the introduction of official inspections of both livestock
and meat the veterinary surgeons responsible for clinical work and
meat inspection have cooperated closely, particularly when animals
have been slaughtered because of illness or other emergencies.
Identification of pathogens
Figure 4 show~ how latent infections may be identified in the
living animal. In general, this is possible by means of additional
67 ~
Method Disease Relia~bility
AP,-FBSA (poultry)
AP (LA, ABR, KBR)
BU droppings (LA)
(see original)
Tuberculosis +
Brucellosis +
Salmonellosis +
Listeriosis (+)
Leptospirosis +
Toxoplasmosis +
Rickettsiosis
Trichinosis
Cysticercosis (§
Fig. 4. Methods of detecting zoonoses relevant to meat hygiene.
allergological, serological and bacteriological tests some of which
are still relatively expensive and must be carried out in the
laboratory.
The intracutaneous test using tuberculin has proved to be the
ideal method for diagnosing tuberculosis in cattle. A member of
our research group has therefore attempted to use the intracutaneous
test for detecting brucellosis in pigs and sheep and has produced
a brucellin on a polysaccharide base. A fairly extensive field test
in Cyprus and in the Soviet Union is now being conducted to
investigate its suitability for mass testing. We did similar work
on the diagnosis of leptospirosis. Obiger and Sch~nberg (1972,
1973) developed a leptospirin from the most important pathogenic
serotypes for an intracutaneous test which is also undergoing field
tests at the moment. If it were possible to use an intracutaneous
toxoplasmin test for the diagnosis of toxoplasmosis in pigs great
progress will have been achieved. Additional tests would be
needed to determine, whether the antigen used could be improved.
An additional improvement would doubtless be the fluorescence
antibody techniques which could replace the laborious Sabin-
Feldmann test. It remains to be seen how far the fluorescence
antibody "technique which we are testing for the diagnosis of
trichinellosis, etc., in cooperation with other Member countries
of the European Community, could replace the microscopic inspection
of meat
Nor is it yet certain whether our tests (walter and GrossMlaus
1972) on the diagnosis of cysticercosis in living cattle by means
of latex agglutinationand indirect haemagglutination and using
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an antigen prepared specially from taenia can ultimately be
successfully developed for practical use. Itwill essentially
depend on whether there are suitable~dentification~methods
aVailable for the proposed herd tests.
Identification of residues
Since 1973 German meat inspection legislation has provided a
legal basis for random samples (1% of all animals) and examination
of suspect slaughter animals. All animal carcases subjected to
bacteriological meat examination are also tested for inhibitory
substances. Because of the importance and occurrence of certain
residues, identification methods for
i. antibiotics
2. oestrogenic substances and
3. anti-thyroid preparations
were developed as priorities and made compulsory. Since rapid
methods are needed, a bioassay using a B. subtilis strain was
prescribed for identifying antibiotics, the mouse uterus test for
identifying oestrogens and histological examination of the thyroid
for identifying anti-thyroid preparations (e.g. methylthiouracil,
propylthiouracil). Although these methods have certain shortcomings
as regards specificity, they have contributed to a marked reduction
in positive findings. In many cases followUup tests on animal
stocks have confirmed the findings. Also, the regular observations
of a veterinary surgeon in practice skouldbe able to prevent
unwanted residues in farm animals.
Analysis of a sample of urine by the agar diffusion test
(Terplan, 1974) will reveal whether inhibitory substances were
administered; The substance must of course be eliminated via the
kidneys; this is true of most antibiotics and sulphonamides,
although bacitracin, sulphaguanidine and a few others are
exceptions. Detection of inhibitory substances in urine is about
as reliable as the compulsory method for detection in meat and
organs. Oestrogenic substances administered parenterally can
be detected by analysis of urine from the living animal. Thin
layer chromatography by the Schuller method (Karg, 1971) is most
suit~l~ for determining diethylstilboestrol. Oestradiol and its
derivatives may be detected by fluorimetry. There is, however,
no reliable method for detecting inti-thyroid substances in the
living animal. It is therefore both necessary and possible for
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clinicians and food hygienists to cooperate closely in protecting
consumers against residues of pharmacologically active substances.
Herd tests in practice
In an earlier publication (Grossklaus, 1973), an attempt was made
to provide a guide to stock tests for veterinary surgeons in practice.
This guide took into account the incubation time of various types
of zoonosis with the aim of providing stock destined for human
consumption with a valid certificate of health before slaughter.
By taking random samples and where necessary repeating tests,
especially in certain bacteriological and serological cases,
(e.g. 3 tests on faeces at three monthly intervals to detect
salmonella, and determining a titration curve in toxoplasmosis),
stock tests do seem feasible. In addition tests for residues would
need to be repeated shortly before slaughter.
But a number of conditions must still be fulfilled before these
tests reach the practical stage. This has led the food hygiene
section of the German Association of Veterinary Medicine to form a
working group concerned exclusively with these problems. It would
be most useful if the World Association of Veterinary Food
Hygienists (WAVFH) could also work on the problems. Figure 5
shows in diagrammatic form the different stages of a herd test.
Veterinary surgeon
Herd
V e t e r i n a r y i n s p e c t i o n o f f i c e and s l a u g h t e r - house l a b o r a t o r y
Therapeutic measures Waiting period Possible postponement Clinical, of slaughter
allergological, serological, and ---}Diagnosis bacteriological "~ examinations Health certificate for
slaughterhouse
Rejection of Approval of diseasedanimals healthy stock
Slaughter animal examination Meat examination
Fig. 5. The different stages of a herd test and the consequences for meat hygiene.
CONCLUSIONS
In considering "The CorrelatiOn of activities in veterinary food-
hygiene work and yeterinary-clinilcai practice"~ .I think that the
comments on existing cooperation and what will be necessary in future
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have shown when herd tests should be used for the early detection
of latent infections and harmful residues of chemical substances in
meat livestock. Figure 6 clearly shows how much clinicians and
food hygienists or clinical and food hygiene knowledge complement
one another in consumer protection. It also shows the many aspects
of the veterinary surgeon's work in helping to protect both the
environment and the health of the general public. Training should
therefore be increasingly concentrated on these tasks.
National and international legislation
Animal hygiene Control of livestock (breeding, housing epidemics and zoonoses disease)
E x a m i n a t i o n o f E n v i r o n m e n t a l p r o t e c t i o n a n i m a l s f o r slaughter and ) and health protection of q Animal nutrition
the general public meat inspection / / ~ I
Foodstuffs inspection Removal of dung and waste water
Removal of carcases
Fig. 6. Participation of various special fields of veterinary medicine in environmental protection and health protection of the general public.
REFERENCES
Bartels, H., 1963. Lecture to the German Association of Veterinary Medicine, 6: iO. 1962. Special edition Parey Verlag, Berlin and Hamburg.
Bartels, H., 1966. Schlacht-Viehhof-Ztg., 66: 508-514. Dutschke, G., 1966. Schlacht-Viehhof-Ztg., 66: 4-8. Grossklaus, D., 1968. Schlacht-Viehhof-Ztg., 68: 461-468. Grossklaus, D., 1973. Fleischwirtshaft, 53: 1721-1725. Kampelmacher, E.H., 1969. Paper read to the 5th Symposium World
Ass. Vet. Food Hyg., Opatija (Yugoslavia). Karg, H., 1971. Paper read to the Conference of the German
Association of Veterinary Medicine on 30.9 in Freiburg. Obiger, G. and Sch~nberg, A., 1972. Fleischwirtschaft, 52:
1458-1460. Obiger, G. and Sch~nberg, A., 1973. Fleischwirtschaft, 53: 1452-1456 Scheibner, E., 1970. Unpublished studies. Terplan, G., 1974. Paper read to the 16th meeting of the Food
Hygiene Section of the German Association of Veterinary Medicine, Garmisch-Partenkirchen 24-27 September.
Walther, M. and Grossklaus, D., 1972. Zbl. Vet. Med. (B), 19: 309-319.
71
KuRZFASSUNG
Grossklaus, D., 1978. Bestandsuntersuchungen bei Schlachttieren zum zum Schutze des Verbrauchers vor Zoonoseerzegeen und chemischen Ruckst~nden. Vet. Sci. Commun., 2: 63-72 (in Englisch).
Die klinische T~tigkeit des Tierarztes beeinflusst wesentlich die Arbeit des tier~rztlichen Lebensmittelhygienikers. Dies trifft besonders for die rechtzeitige klinische, allergologische, serologische und bakteriologisch-virologische Untersuchung von Schlachttieren in ihren Best~nden zu, wie sie u.a. von Bartels, Kampelmacher und Grossklaus vorgeschlagen wurde. Sie soll u.a. die Diagnose inapparent verlaufender Zoonosen erm6glichen, die sonst im Rahmen der amtlichen Fleischuntersuchung unerkannt bleiben. Der pathologisch-anatomische Befund aus der Fleischuntersuchung ist zudem wichtig fflr den Kliniker. Hinzu kommen erforderliche Massnahmen zur Ausschaltung von toxikologisch relevanten R~ckst~nden~ pharmakologisch wirksamer Substanzen. Anhand eigener Untersuchungen web, den Vorschl~ge f~r sog. Bestandsuntersuchungen unterbreitet die in der Lage sein k~nnten, den internationalen Handel mit vom Tier stammenden Lebensmitteln sicherer zu gestalten und zu f~rdern.
REsuME
Grossklaus, D., 1978. Inspection v~t~rinaire des animaux de boucherie au niveau des @l~vages pour protEger les consommateurs contre les agents de zoonoses et les residus chimiques. Vet. Sci. Commun., 2: 63-72 (en anglais).
L'action du v~tErinaire praticien a une influence primordiale sur le travail du v~tErinaire hygiEniste. Cela est particuli~rement vras pour l'examen clinique, allergologique, sErologique et bactEriologique des animaux de boucherie, au niveau des ~levages, propose par des auteurs comme Bartels, Kampelmacher et Grossklaus. Il doit rendre possible le diagnostic des zoonoses inapparentes qui risqueraient de passer inapercues au stade de l'inspection des viandes. Du reste, le diagnostic anatomo-pathologique resultant de l'inspection des viandes est important pour le clinicien. Ii faut ajouter les mesures n~cessaires pour ~liminer les r~sidus toxiques provenant de substances pharmacologiques actives. En se basant sur ses propres Etudes, l'auteur fait des propositions pour des examens dits des "troupeaux" qui pourraient rendre plus sQr et plus efficace le commerce international des dentEes d'origine animale.
7~
RIASSUNTO
Grossk!a~s,~.~.~i1978.~ Ispezione veterinaria degli animali da macell~ neglial~evamenti~p~ la protezione dei consumatori contro gli agenti di~z!oon~si~ed!i residui chimici. Vet. Sci. Commun., 2:: 63-72 (in Inglese).
L'at~iVit~ del medico veterinario influenza sensibilmente il lavoro~dell'~ge~ista Veterinario-alimentare. QuestO vale in partlcolere per: l'4same clinico, allergico, sierologico e batteri61ogfCodegi~ animali da macello negli allevamenti, proposti da aut'or~ quali Bartels, Kampelmacher e Grossklaus. Gli esami'debbono permettere la diagnosi delle zoonosi inapparenti che rischierebbero di passare inosservate in fase di ispezione delle carni. Pertanto la diagnosi anas risultante dall'isPezione delle carni ~ importante anche per il clinico. A cio' sl devono aggiungere misure atte ad eliminare i residui tossici provenienti dalle sostanze farmacologiche attive. Basandosi sui suof studi, l'autore fa proposte relative agli esami dett• di "mandria" che potrebbero rendere pi~ sicuro e efficace il commercio internazionale ~egli alimenti di origine animale.