MEAT BORNE DISEASES
Dr.Kedar Karki,
VS,Nepal
Consumption of meat by human being is evident since the dawn of civilization. By experience, people learnt that the flesh of sick animals may lead to serious consequences of health deteriorations. As the meat industry started developing, in the process of producing slaughtering, processing, distribution and storage, the importance of meat borne diseases has been realized. Meat borne diseases can be discussed under three headings;
(i) meat borne diseases of chemical toxicological origin, (ii) animal diseases transmissible to man through meat consumption and
(iii) environmental contamination of meat and meat products and bacterial food poisoning.
A. Meat-borne diseases of chemical or toxicological origin.
The flesh of any of the mammalian or avian species is not poisonous. But it becomes poisonous when livestock consume poisonous plants. Even after the death also the concentration of alkaloids remain high enough to cause illness in the persons who consume such meat. So, it is better to avoid those animals which are constantly dependent on poisonous plants. Even if the alkaloids or other toxic substances do not accumulate in muscle tissues, certain visceral organs especially the liver which act as a detoxifier and the storehouse of specific biochemical, may contain sufficient quantities of toxic substances which may be harmful to human health when consumed, are being mixed up with the meat and meat products.The other form of possible danger is that the excessive addition of organic and inorganic chemicals as preservatives. If they are added in more than permissible limits, they may cause serious diseases in human beings. Antibiotics on the other hand which are added to inhibit bacterial growth also may upset the health of the consumers. The meat kept exposed like in restaurants, canteens, bakeries and abattoirs would get contaminated when any insecticide is being sprayed
B. Animal diseases transmissible to man through meat
During handling and slaughtering of food animals and while dressing for meat purposes there is a possibility of transferring infectious agents from animals to man. The infection would spread not only from the digestic tracts but also through the abraded and broken skin. The important meat borne diseases are as follows.
1. Anthrax:
The countries in which efficient methods of inspecting meat and meat products are existing, there are remote chances of infection with anthrax. But this disease is still not completely eradicated from domestic animals, so there is a potential threat which requires careful preventive measures by those handling the animals. Human beings get infected with these diseases either through the skin (malignant pustules) or through the lungs (wool sorters or rag sorters disease). Infection by ingestion has been reported in some tribals who are not careful about the source of meat and its cooling temperature.It has also been reported that while handling the anthrax affected meat if the person had any cut or injury those per- sons have died in few days on account of septiccamia, haemorrhegic leptomeningitis due to Bacillusanthracis. Hides wool shaving brushes made from infected hog bristles have sometimes spread the disease to human beings. But this hasbecome very rare due to availability of effective sterilization methods. It has antimortem and postmortem symptoms by which we can judge the disease.
a. Antimortem examination
Depending on the species, clinical symptoms vary. CattIe, sheep and goats are highly susceptible in which the disease is seen as a fulminant form of septicaemia and the affected animal die in a very short time. In less severe form of disease the animals show high fever and general constitutional disturbances. Bloody discharges from natural orifices/openings are commonly observed. However, less susceptible animals like swine exhibit no characteristic symptom. Usually this disease would occur in a chronic form in: swine but in some cases only local infection of the pharynx and enlargement of the cervical lymph nodes are noticed.
b. Postmortem examination
In the postmortem examination one may find greatly enlarged spleen engorged with dark unclotted blood. In hogs and the emergency slaughtered cattle, sheep and goats, enlargement of spleen may be slight or absent. Petechial haemorrhages are observed especially beneath the pericardium and pleura. We can confirm with microscopic examination of stained smears from the splenic pulp, the lymph of the mesentric glands, the blood veins of the skin, etc.
c. Precautions
The meat of the animals affected with anthrax is unfit for consumption and should be destroyed. If the animals antemortem examination detects anthrax its slaughter should be forbidden. All possible measures should be taken up for preventing the dissemination of the disease.If the disease is detected during the postmortem examination, all the instruments like knives, saws, scissors, etc., which come into contact with the infected carcass should be sterilized. The slaughter house and the premises should be disinfected with 2% lye solution. It essential to examine all persons involved in the slaughtering and handling the animals for any possible cuts and wounds. Immediate medical aid should be sought for the treatment. Every necessary care should be taken to ensure that the infection do not get transferred from diseased to healthy ones.
2. Tuberculosis:
After a debate in the international conferences, it has been concluded that tuberculosis affected animal meat is unfit for consumption and necessarily be destroyed. But later after a result of deliberations it was declared that the infected animals can be condemned only if the disease has been acute miliary tuberculosis or where a recent collapse of the organic defences has been observed or when the disease is accompanied by cachexia. Otherwise after the careful destruction of tuberculous lesions the meat can be consumed. This solution is acknowledged as it prevents the wastage of valuable animal protein. It was unknown that the muscle portion of the animal which is eaten as meat is a poor culture medium for tuberculocis bacilli. It is essentially, an infection of reticulo-histiocybic system. After gaining this knowledge it was accepted that the meat of tuberculosis affected animal need not necessarily be destroyed. The meat inspectors should be well versed with the diagnostic symptoms of tuberculosis as the pathological lesions gives a good indication of the stage of the disease when the tubercle bacilli pass through the blood stream so as to bring about generalization.
a. Antemortem inspection
The clinical symptoms of this disease become apparent only when it reaches an advanced stage. Even then one cannot be surely confirm of tuberculosis symptoms. However, nodular swellings of lymph nodes, hard tight skin, and rough coat of hair are the suspicious symptoms of the disease. In hogs exostosis and curvature of the spine without rachitic symptoms should arouse suspicion of the disease.
b. Postmortem examination
All lymph nodes should be thoroughly examined which include bronchial mediastinal submaxillary retropharyngeal and mescentric tissues. The characteristic lesion is the tubercle which usually takes the form of a firm or hard white grey or yellow nodule. In cattle, calcification is common particularly in the lymph nodes. As such tubercles are cut they give a gritty sensation and grating sound. In the case of pearl disease, a form of tuberculosis, pleuritic or peritonitis, large masses of smooth grape like bodies are found covering the surfaces. In lung tuberculosis there are strong and firm adhesions of the lungs to the chest wall and removal of the lungs from the cavity is difficult. The lung lesions usually take the form of case of calcareous tubercles.Active and recent lesions show hyperaemia around the periphery ot’ caseous masses whereas old inactive lesions be- come calcareous and encapsulated. Occasionally a tubercle may break into a blood vessel resulting in the lodging of a large number of tubercle bacilli in the capillaries of the parenchyma of visceral organs where they give rise to myriad tu- bercles looking like sprinkling of millet seeds. Hence the name “miliary tuberculosis” is given to it.
The incidence of tuberculosis among goats and sheep under natural conditions is very low when compared with that in cattle and buffaloes. However, both these species of animals are highly susceptible to infection with tubercle bacilli of the bovine type and readily get infected to the disease on coming in close contact with tuberculous cattle.
c. Preventive measures
Carcasses of tuberculos animals should be seized when they are caught up with cachexia or acute miliary tuberculosis or tuberculous lesions indicating a recent collapse of the organic defences ie. massive caseous tuberculosis of an organ, acute exudative tuberculosis of the pleura peritoneum pericardium, etc.In tuberculosis of serous membranes, the wall of the corresponding cavity would be destroyed. Any organ with a tuberculous lesion or where the corresponding lymph node has a tuberculous lesion should be destroyed. If the disease is found in bone whole skeleton is to be destroyed. In other cases, carcasses can be released for human and animal consumption subject to careful extirpation (to remove) and destruction of all tuberculous lesions.
3. Brucellosis:
Brucellosis is often transmitted to man with the consumption of meat and meat products. But some minor abrasions of skin and mucous membranes also serve as entry of infection. The personnel handling the meat trade are also susceptible to this disease. In such cases control of brucellosis is very difficult till the disease can be eradicated from animals, since handling of livestock, slaughtering, etc. are unavoidable.It is not easy to identify the brucella infected animals during ante and post mortem examination. But serro-agglutination test indicates the disease. Efforts are being underway to develop more easier methods of confirming this disease but presently this seems to be difficult to attain such standards of disease control in the near future. So, educating the meat handlers and improving the sanitation of slaughter houses are the preventive measures that are recommended.
4. Salmonellosis
If the meat of animals infected with salmonellosis is inadequately cooked such as underdone beef steaks, gently fried sausages, large masses of roasted meat with improper heat, etc, and if it is consumed, this diseases occurs in man. Apart from this, contamination of meat by the persons handling it or contamination in course of manufactured and processed meat products or its contamination with faeces of livestock, rodents, pet animals, etc during storage are also the sources of contamination.Several species of salmonella group produce powerful toxins like bacterial toxins, toxalbumins, toxigenic substances, etc. which on ingestion produce meat poisoning. The activities of the micro-organisms may be accentuated during storage under heat and damp conditions and make the meat poisonous. Some species grow luxuriantly in the muscular tissue even at a low temperature (10 degree C).There are no typical clinical symptoms of meat poisoning due to salmonellosis in human beings. But symptoms like nausea, cramps, vomiting, diarrhoea can be correlated with it provided the animal is not suffering from any other disease. As such it is difficult to identity salmonellosis affected animals. However by improving the standards of meat inspection and hygiene, it is possible to reduce the incidence.
5. Botulism
Soil and polluted water are the chief natural habitats of spores of Clostridium botulinum. Occasionally pigs and certain types of fish such as the sturgeon act as intestinal carriers. Botulinic syndrome is basically due to ingestion of performed toxins in the food material. Hence, contamination of meat with soil, especially when it is to be preserved for some period, should be carefully avoided. In pork, infestation may be caused by exterior soiling or by invasion of botulinum organisms from the intestinal tract in the case of carriers.
a. Preventive measures
Since the spores of Clostridium botulinum are practically confined to the soil and to animal faeces special care has to be taken to avoid conveying soil organisms during the process of slaughtering and dressing. Meat should be kept under dust proof conditions. Surface contamination with spores of C. botulinum is less troublesome but sometimes they may get lodged beneath meat surface were oxygen tension is low which increases their germination rate. Then the motile vegetative forms of the organisms move into deeper strata and multiply rapidly with production of toxins.To avoid contamination from animal faeces all operations in the slaughter house should be carried out under strict hygienic conditions and the animal intestines used for sausage casings must be meticulously cleansed. Care should be exercised at all stages in the preparation of preserved meat and sausages and bacteriological standards should be strictly followed to ensure freedom from contamination with pathogenic micro-organisms.
The following precautions will help in reducing the incidence of bolutism.
1. Preserved meat preparation which emit a rancid or butyric acid like odour should not be consumed.
2. Preserved meat preparations should preferably cooked before consumption and not eaten in a raw state.
3. For pickles, brine solution of at least 10% common salt should be used because at this concentration, the growth of C. botulinum is hampered.
6. Staphylococcal meat intoxication:
Enterotoxin which is a toxic metabolite is produced by certain strains of staphylococus on many types of foodstuff including meat and meat products. It does not change the appearance, odour and taste of the products. This substance causes disturbances in gastro intestinal tract and provokes vomiting and diarrhoea by specific effect upon the central nervous system.To prevent the formation of enterotoxin, the following characteristics of entertoxin are to be considered.
a. Ubiquity of the causal microorganisms of this group.
b. Complexities in determining enterotoxigenic strains.
c. The formation of enterotoxin in foodstuffs including meat and meat products even at a relatively low temperature.
d. Comparatively high resistance to heat.
These characteristics cause hindrances. These are to be tackled by minimizing the chances of a access of enterotoxigenic staphylococci to meat preparations, by applying enough heat to destroy the staphylococcal contaminants and by refrigerating at lower temperatures to inhibit the production of enterotoxin.Prevention of enterotoxin production in meat and meat products is difficult because of the ubicuitous presence of the organism. To minimise the contamination, attention should be paid to personal hygiene. Any person known to be a carrier of this organism should be prevented from handling operations unless it is certified that the organisms in the nasopharynx lack food poisoning propensities. Keeping the meat under coverage helps to reduce contaminations. Refrigeration is the most effective method to prevent contamination and if this facility is not available, the meat should be kept cool by other devices. For canned meat, enough heat should be applied to ensure destruction of the organism. The central portion of the meat should be heated to 65 degree C for 30 minutes to ensure safety from contamination.
7. Taeniasis:
Measly beef (Cysticercus bovis) and measly pork (Cysticercus cellulosae) are sources of adult tapeworms to human being when consumed in an inadequately cooked form or as raw sausages. These measly organisms of cattle and pigs are readily visible to the naked eye. For a thorough inspection of the carcass several cuts should be made in the muscles. The inner and outer muscles of mastication and the tongue musculature should be particularly examined. Heavily infested meat should be destroyed while lightly infested meat should be made harmless by thorough boiling salting and pickling.
8. Trichinosis:
This disease occurs in human beings following consumption of raw inadequately cooked or improperly cured infected pork. In tropical countries where meat is thoroughly cooked the incidence of this disease is low or absent. Besides pigs, infected meat of wild boars, bear, etc, is also a source of human trichinosis.Trichenae are found in greatest numbers in the diaphragmatic tissues and muscles. Next in the order of frequency are the tongue, laryngeal, lumber masticatory and abdominal muscles.Trichonis meat is definitely harmful to health but fat from these carcasses can be used. The muscle trichinae are not very resistant to the heat. Heating at 62-70 degree centigrade kills the parasites and makes them safe for human consumption. Salting and pickling of meat also destroys them in 4-6 weeks.To avoid ill health from all these above mentioned disease and contaminations, it is essential to carefully examine the meat during inspection.
MEAT BORNE DISEASES & ZOONOSES
MEAT BORNE DISEASES & ZOONOSES
