Public health aspects of microbial contaminants in food

Food-borne diseases affect the health and welfare of hundred thousands of people and result in considerable economic loss. Salmonella and Campylobacter are by far the most important causes of food-borne illness. Raw foods of animal origin are the major sources of these pathogens. Mishandling of foods in kitchens contributes to food-borne disease outbreaks. More education is necessary. But because of the inevitable risk of recontamination of cooked foods in every kitchen, more emphasis should be placed on pathogen-free raising of food animals and good manufacturing practices during slaughter. This will minimise contamination of raw foods of animal origin, thus reducing the contamination pressure in the kitchen and more effectively controlling food-borne diseases.     

Public health aspects of dirofilariasis in the United States

Coin lesions in the human lung present significant differential diagnostic problems to the physician. There are at least 20 known causes of such lesions, including neoplastic lesions, infectious diseases, and granulomas. The human medical literature contains many misconceptions about the life cycle of Dirofilaria immitis, including the method of entry of the infective-stage larvae and the development of the young adult worm. These misconceptions have obscured the recognition of the clinical presentation of pulmonary dirofilariasis and the potential for D. immitis to lodge in many other areas of the human body besides the lung. Exposure to infective larvae of D. immitis is more common in humans than is currently recognized. Reported cases in humans reflect the prevalence in the canine population in areas of the United States. The veterinary literature provides compelling evidence that D. immitis is a vascular parasite, not an intracardiac one. Its presence in the right ventricle is a post-mortem artifact, because it has never been shown to be there by echocardiography or angiography in a living dog, even though these techniques have demonstrated adult D. immitis in the pulmonary, femoral, and hepatic arteries; posterior vena cava; and right atrium of live dogs. Physicians have taken the name "heartworm" literally, believing that the worm lives in the heart and only after it dies does it embolize to the pulmonary artery. However, the coin lesion is spherical in shape, not pyramidal, as embolic infarcts to the lung in humans are known to be. The coin lesion is an end-stage result of the parasite's death in the vascular bed of the lungs and the stimulation of a pneumonitis followed by granuloma formation. This pneumonitis phase of human pulmonary dirofilariasis is often not recognized by the radiologist because of the way pneumonitis is diagnosed and treated and because the developing nodule is obscured by the lung inflammation. Serologic methods for use in humans are needed for clinical evaluations of patients with pneumonitis living in highly enzootic D. immitis regions. As well, epidemiological surveys are needed to determine the real extent of this zoonotic infection.     

Human health aspects of antibiotic use in food animals: a review

Antibiotic use not only selects for resistance in pathogenic bacteria, but also in the commensal flora of exposed individuals. Veterinary surgeons regularly prescribe antibiotics for food animals to treat bacterial infections just as doctors do for human patients. In addition, however, animal feeds contain added antibiotics not for therapy but for economic reasons: to enhance the growth rate of these animals. Several of the antibiotics used as growth promoters are analogues of and fully cross resistant with important antibiotics used in human medicine. As a result of this high exposure to antibiotics, the prevalence of resistant bacteria in the faecal flora of these animals is high. These resistant bacteria can be directly and indirectly, via foods of animal origin, transferred to humans and either colonize the human intestinal tract or exchange their resistance genes with commensal bacteria of humans. As the intestinal flora functions as a reservoir of resistance genes for pathogenic bacteria and because many bacterial species of the intestinal flora are potential pathogens, the efficacy of antibiotic therapy in human medicine may be jeopardized.     

Public health and research perspectives on the microbial contamination of foods

Scientific advances in methodology and epidemiology have resulted in a renewed awareness of foodborne disease, and increased contact among nations of the world has stimulated rapid global distribution of foods as well as foodborne pathogens. New food vehicles are being identified for old, familiar pathogens, and new pathogens are being discovered. Current research in food microbiology has spurred development of rapid and specific methods to identify these pathogens and to assess their virulence. Organisms of recent interest, such as Bacillus, Yersinia, Campylobacter, Listeria, Sporothrix, Giardia, Cryptosporidium, and Anisakis, are the foci of new investigations, as are the more familiar foodborne pathogens, Salmonella, Shigella, Clostridium, Staphylococcus, Entamoeba and Ascaris. Some foodborne organisms, such as parasitic protozoa, serve as hosts for unique bacterial and viral symbionts but also might become infected with mammalian viruses. The remote possibility of the transmission of human immunodeficiency viruses in foodborne protozoa is discussed.     

Effects of animal housing facilities on residues and contaminants in food

There are--especially in the case of food of animal origin--only a few well-controlled studies available comparing organically and conventionally produced food with a focus on residues and contaminants. The differences found seemed to be much lower than expected, and the amounts of residues and contaminants were mostly below regulatory maximum residue levels. In the case of organically and conventionally produced milk there have been slight but usually not significant differences reported. One important observation is, that conventionally produced milk contains aflatoxin M1 more frequently than biologically produced milk. The investigation of eggs from different housing systems for laying hens showed in the case of dioxins the highest concentrations in free range eggs. In contrast, propoxur, an insecticide used against the poultry red mite, was found in eggs from battery cages in higher amounts than in those from enriched cages and in eggs obtained from an aviary system. Further research in this field is highly recommended, but there should be more sophisticated evaluation of the data sets from national and international monitoring programs.     

Public health aspects of bacterial drug resistance in modern battery and town/village poultry in the tropics

A correlation of antibiotic use and drug resistance was found among Escherichia coli strains isolated from battery poultry in the University of Ibadan Teaching and Research Farm. All the E. coli strains from battery birds were resistant to Tetracycline, Streptomycin and Sulphonamide (Sulphafurazole) by the disc sensitivity test. In contrast, all the strains isolated from free range town and village poultry were sensitive to the range of drugs tested, while the Minimal Inhibitory Concentrations of the drugs against these free range isolates were the same as those for the control E. coli strain N.C.T.C. 10418. Ninety-eight to 100% of the strains from both battery poultry and from town/village birds were sensitive to Colistin, Chloramphenicol, Nitrofurantoin and Nalidixic Acid. Since antibiotic-resistant Escherichia coli from animal sources are known to be indistinguishable from those found in man, the indiscriminate use of antibiotics is potentially capable of giving rise to a higher incidence of intractable infection with resistant bacteria. These drug-resistant organisms may be transmitted from animal to man, and complicate the therapy of human diseases.     

Public health advocate

With antimicrobial resistance mounting, an important public health goal is to preserve therapeutic effectiveness of remaining antimicrobials. To that end, fewer antimicrobials should be used in human medicine and in agriculture. Public health initiatives to reduce antimicrobial overuse could benefit from concurrent collection of agricultural usage data; they could aid scientific understanding of the resistance problem and confirm the efficacy of interventions. Data collection in this context should be a priority. However, usage data are nonessential to achieving the public health goal. U.S. regulation of agricultural antimicrobials today is very reliant on risk assessment. While more data can be useful for use in risk assessment, microbial risk assessment itself may not be well suited to the purpose of reducing antimicrobial overuse. Among other recognized shortcomings, current microbial risk assessment models typically fail to account for the essential ecological nature of antimicrobial resistance. This makes it inadequate for fully characterizing the human health or ecological risks of animal antimicrobials. European success at phasing out unnecessary antimicrobial usage in agriculture, on the other hand, has derived from decisions based on public health concerns and political will, and not on the collection of usage data or on the successful completion of a risk assessment.     

Gastrointestinal aspects of food allergy: A review

Food allergy in dogs and cats, although rare, is a well recognised cause of skin disease. However, despite reports of conditions responding to dietary manipulation, evidence for gastrointestinal manifestations of food allergy is scarce. Difficulties involved in reaching a clinical diagnosis of food allergy are discussed in an attempt to explain this enigma. The distinction between food allergy and intolerance, the complexity of the gastrointestinal immune system and the limited understanding of the mechanisms by which food allergy develops are reviewed.     

Long-term cryopreservation of microbial strains relevant to food hygiene

Experiments on long-time cryopreservation at -20 degrees C were conducted, using 42 microbial strains of relevance to food hygiene. Blood slant agar was coated with 10% glycerol solution, so that all strains were in re-culturing conditions, following 12 months of storage. Re-culturing of 18 in 20 of the microbial genera used in the experiment was possible after 24 months of storage, if strains had been kept only in 10% glycerol solution. The method proved suitable particularly for strain keeping of highly sensitive genera (Lactobacillus, Pseudomonas, Aeromonas, Shigella).     

Public health and policy

Antimicrobial agent usage data are essential for focusing efforts to reduce misuse and overuse of antimicrobial agents in food producing animals because these practices may select for resistance in bacteria of animals. Transfer of resistant bacteria from animals to humans can lead to human infection caused by resistant pathogens. Resistant infections can lead to treatment failures, resulting in prolonged or more severe illness. Multiple World Health Organization (WHO) reports have concluded that both antimicrobial resistance and antimicrobial usage should be monitored on the national level. The system for collecting antimicrobial usage data should be clear and transparent to facilitate trend analysis and comparison within and among countries. Therapeutic, prophylactic and growth promotion use should be recorded, along with route of administration and animal species and/or production class treated. The usage data should be compared to resistance data, and the comparison should be made available in a timely manner. In the United States, surveillance of antimicrobial resistance in foodborne bacteria is performed by the National Antimicrobial Resistance Monitoring System (NARMS) for enteric bacteria, however, the United States still lacks a mechanism for collecting antimicrobial usage data. Combined with antimicrobial resistance information from NARMS, antimicrobial usage data will help to direct education efforts and policy decisions, minimizing the risk that people will develop antimicrobial resistant infections as a result of eating food of animal origin. Ultimately mitigation strategies guided by usage data will be more effective in maintaining antimicrobial drugs for appropriate veterinary use and in protecting human health.