Rev. sci. tech. Off. int. Epiz., 1995,14 (1), 177-189

Aircraft and ship disinfection F.M. CANCELLOTTI *

Summary: Shipment of animals, animal products and foodstuffs (for human or animal consumption) by sea and air is economically important. However, the possibilities of pathogen transmission represent a genuine danger, even if veterinary controls are performed continuously.

Bacteria, viruses, fungi and parasites excreted by animals may contaminate surfaces and are protected by organic matter.

Cleaning is an important step in the sanitising process, and if this is performed well, more than 90% of microorganisms can be removed.

Chemical disinfectants must be compatible with cleaning procedures, instruments and materials used previously, and should be without harmful effects on humans or animals.

The author outlines the basic procedures and fundamental principles involved.

KEYWORDS: Chemical disinfection - Cleaning - Excretion of microorganisms - Stress - Surface contamination - Transport.

INTRODUCTION

Shipment of animals, foodstuffs (for human or animal consumption) and products of animal origin always represents a risk factor from an epidemiological point of view (11). Transport of these materials represents a constant threat, even if veterinary controls are correctly and continuously performed both before and after shipment (13). All modes of international transport are potentially hazardous for animals and can lead to disease, stress and compromised welfare (1,3,15,16).

Veterinary services opera te to prevent the diffusion of major epizootic diseases (e.g. foot and mouth disease, bovine pleuropneumonia, rinderpest, African swine fever and classical swine fever [hog cholera]) and to prevent the spread of less invasive but nevertheless very important diseases (e.g. bovine tuberculosis, brucellosis and leukosis) (15).

When domest ic or non-domest ica ted animals are crowded together, a stressful situation originates which may prove dangerous for animals with potentially harmful microbial populations and differing levels of immunological defence.

Health and animal welfare are linked; one cannot be considered without the other (15). Disease may arise as a result of infection with a specific bacterial or viral agent, but disease can also occur due to a shift away from the normal physiological balance. Such changes from normality can predispose animals to viral or bacterial infection.

* Istituto Zooprofilattico delle Venezie, Via Orus 2, Padova 35100, Italy.

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The stress response, together with the general adaptat ion syndrome (resulting in changes in the immune system and reduced resistance to infection), is important and well documented. Accordingly, stress is linked with disease in two ways, as follows:

- Stress itself could be considered as a disease of adaptation and can also predispose to other diseases (1).

- Stressed animals, even if in an apparently healthy state, can excrete pathogenic organisms and contaminate their environment; this is the first and essential step which perpetuates the cycle of infection.

The dynamics of pa thogen shedding (i.e. numbers excreted at any time and the duration of shedding) vary between diseases (12), and pathogens vary greatly in their ability to resist unfavourable condit ions, such as exposure to ultraviolet light and (particularly) to drying. Many factors influence the survival of pathogens. In general, microorganisms are protected by the presence of organic materials (e.g. pus, serum and faeces) (12). Microorganisms which produce spores are very resistant to chemicals, heat and drying.

In addition, the presence of an undesirable 'guest' population (e.g. mice, rats, ticks, horse flies, mosquitoes) is often associated with living animals, foodstuffs or animal products. All of these species represent dangerous infection carriers and can be moved easily by sea and by air. A primary problem is the contamination of vehicles and various types of equipment by faecal material, urine, blood, skin fragments, mucus and other discharges released by animals, and unwanted 'guests ' . This is relevant to hygienic control, and mandatory measures therefore include efficient cleaning and disinfection of transport vehicles and equipment, prevention of entry of potential insect or small animal vectors of disease into transport vehicles, and the provision of uncontaminated feed and water (15).

Long-distance transport by sea or by air has been covered in several reports, and the problems involved in the disposal of effluent and carcasses are of particular concern (1 ,3 ,4 ,5 ,16) .

Different regulations have been issued by various administrative bodies. The most relevant guidelines to be considered are contained in the comprehensive United Kingdom Animal Health Act (5), the Live Animals Regulations of the International Air Transport Association (IATA) (4) and the International Animal Health Code of the Office International des Epizooties (OIE) (16). More recently, European Community Directive 91/628/CEE recalled the importance of sanitising procedures for ships and aircraft used to transport animals (3).

The conditions for transport of animals by sea and air have improved with general advances in comfort through vehicle design, and navigation aids which increase the oppor tuni ty for avoiding turbulent weather (15). Many former concerns about air transport of animals have been satisfied by advances in the design of aircraft and the application of the comprehensive IATA regulat ions (15). These regulat ions have become the accepted guidelines for the Convent ion on In ternat ional Trade in Endangered Species of Wild Fauna and Flora (15) and the OIE (16), and have been employed by the Council of Europe in the development of codes of conduct for the transport of animals (3).

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SAFETY

Cleaning and disinfection procedures involve the use of potential ly hazardous chemicals and specialised equipment, and the following basic procedures should be observed to guarantee the safety of workers and to protect materials and products (14):

a) The chemicals used are often corrosive and toxic. They must therefore be handled with care, in accordance with the instructions of the manufacturer, and must be stored in a secure place.

b) The electricity supply must be switched off when the washing process is performed.

c) All appliances powered by electricity must be properly maintained and handled.

d) Dust and aerosols may be dangerous; all staff should wear protective masks, boots, coats, trousers and gloves.

e) After fumigation, adequa te venti lat ion is necessary before the re-entry of personnel.

f) Structures, machines and instruments must be protected to avoid corrosion and other damage.

g) Caut ion should be exercised to protec t products of animal origin or living organisms (e.g. eggs, animal foodstuffs, embryos, semen, apiaries).

SURFACES AND INSTRUMENTS

A primary factor to be considered is the kind of surface to be treated. Springthorpe and Sattar (19) reviewed the fundamental aspects of this problem. The surfaces likely to carry contaminat ing microorganisms may be categorised as non-porous or porous .

Non-porous, inanimate surfaces may be termed 'hard ' surfaces. Functionally, this group of surfaces may be divided into instruments (which can be soaked in detergent or/and disinfectant solution be tween use) and environmental surfaces and objects (which are usually decontaminated by wiping with solutions). The definition of a hard surface is broad enough to cover everything from egg shells to cement , including stainless steel, aluminium, plastics, ceramics, glass and painted surfaces.

Porous surfaces are the most critical from a hygiene point of view and are mainly represented by wood, plywood, chipboard , formica and varnished surfaces. No environmental surface is completely 'clean': there is always some adherent organic matter. Any surface in contact with animal skin or secreted and excreted matter will acquire microorganisms, sebum components and other molecules from the skin surface. Any horizontal surface will become coated with dust part icles, oily emulsions, desiccated fat, body fluids, etc. (19).

Microorganisms are incorporated in layered soilage. The contaminated surfaces represent a complex challenge to cleaning and disinfectant solutions (19). Disinfectant efficacy on surfaces will be influenced by factors associated with the surface itself - the type and topography of the surface and its 'wetability' - and by the levels and nature of other chemical and biological residues. It should be noted that repea ted use of antimicrobial solutions which act as fixatives (e.g. alcohols and aldehydes) may help to build up residual soilage on surfaces.

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Soilage and contaminating microorganisms are not necessarily exposed at the top layers of the contaminated surfaces. In porous surfaces, the contaminants penetra te between the structures and fill the holes and every irregularity of the surface structure. All surfaces - even 'hard ' surfaces - tend to become further scratched and cracked during use, and to accumulate soilage which is resistant to removal by cleaning and disinfectant agents. The presence of soilage on inanimate surfaces and the surface topography may interfere with the ability of the disinfectant to completely wet the contaminated surface. Hence, components with surface-active properties are desirable in all disinfectant formulations designed for use on surfaces (19).

The surface must be properly rinsed before disinfection is performed. The rinsing fluid must be compatible with the chosen disinfectant, as soaps and detergent residues on surfaces may interfere with the subsequent action of certain disinfectants (19). Table I indicates the various degrees of ease with which a selection of surface materials may be cleaned.

TABLE I

Materials employed in animal facilities and vehicles (Adapted from 14)

Material Ease of cleaning

Phenolic resin coated on plyboard Bituminous paint and boat varnish

on plyboard

Oil-tempered hardboard Silicone-treated chipboard

Glazed and ceramic tiles Laminated plastics

Wood and wood products Asbestos Cement Galvanised steel

CLEANING

The cleaning phase is the stage at which the greatest numbers of microorganisms can be removed (approximately 90% if the process is performed thoroughly) . The procedure described below is most effective when surfaces are free from organic matter. The steps in the cleaning process may be summarised as follows:

a) remove all gross dirt and all movable equipment and animal facilities (e.g. cages and walls)

b) rinse surfaces if necessary

c) apply the cleaning solution

d) wash again.

Very easy

Fairly easy

Difficult

Very difficult

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CLEANING AGENTS

A wide choice of cleaning agents is available, including alkalis, mineral and organic acids, and cationic, anionic or non-ionic surfactants (10,14). The criteria for selection of cleaning agents are as follows:

- suitable for the surface to be cleaned and non-corrosive

- able to remove the type of soil present without leaving any sort of residue

- compatible with the water supply.

A suitable detergent must have adequate wetting properties to enable the solvent (usually water) to contact all areas, by reducing the surface tension and facilitating penetra t ion into all cracks, pinholes and porous materials (10). In addit ion, the detergent should disperse any aggregates of soilage into small particles, and retain any insoluble material in suspension, so that this may be easily flushed from the surface. The detergent itself must be rinsed away without leaving a deposit on the surface.

Ideally, only soft water should be used for cleaning; where this is impracticable using the local water supply, water conditioning or sequestering agents may be added. If very hard water is used, it may be necessary to incorporate an acid rinse into the cleaning cycle to prevent scale formation (10).

Detergents themselves may have a lethal effect on microorganisms and are mainly used at 50-60°C, while some disinfectants may exert a detergent action (10,14, 20). Detergents are usually composed of one or more surface-active agents, and one or more complementary agents (e.g. sequestering, dispersing, complexing, oxidating, suspending or deodorising products) which enhance the power of cleansing products themselves.

Each type of surface-active agent has different properties:

- anionics, salts of complex organic acids, are good detergents but poor bactericides

- non-ionics, organic compounds but not salts, have good wetting powers

- cationics, salts of complex organic bases, are good bactericides but have lesser detergent properties.

Cationic and anionic compounds must not be used together, but their properties are combined in amphoteric compounds.

Table II summarises the properties of surface-active agents.

Cleaning agents are often more effective when used hot, but temperatures of 65°C should not be exceeded when removing fat-containing films, as the emulsion formed with the detergent is destroyed at higher temperatures. This temperature restriction also applies to some alkaline detergents when used with hard water. Acidic cleaners are normally used cold.

It is sometimes useful to combine the cleaning and sanitising stages, but this is only successful where soiling is light and the level of microbial contamination to be removed is relatively low. Not all detergents and disinfectants are compatible, and this must be checked if new combinations are used (10,14,20).

Three main types of detergents are available, as follows:

a) alkaline detergents formulated with chlorine-liberating compounds

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Property Soap Sulphates Sulphonates Non-ionic

Detergent power H S M H Dispersing action M S H H Wetting property M S H H Foaming power M s H I Foam stability H s M I Activity/concentration M S H H Chemical resistance I s H H Hard water resistance I s H H Solubility M s H H Harmfulness to skin L L H H

H: high S: sufficient M: mediocre I: insufficient L: low

b) alkaline detergents formulated with quaternary ammonium compounds or non-ionic surfactants

c) acid detergents with iodophors.

In conclusion, meticulous cleaning of ships and aircraft is usually sufficient to remove and neutralise the microorganisms excreted by animals. Nevertheless, the relevant veterinary authorities may prescribe more rigourous programmes involving disinfection.

CHOICE OF CHEMICAL DISINFECTANT

Many different types of antimicrobial agents are available, serving a variety of purposes (18). In veterinary practice, chemical agents form the most widely-used means of disinfection (17,18).

Numerous reports and reviews on aspects and methods of disinfection in veterinary practice present guidelines for operators (2 ,5 ,6 ,7 ,8 ) .

The efficacy of a chemical disinfectant is mainly determined by the conditions under which it is used. The following factors and variables may influence the choice and the efficacy of disinfectants:

- price - ease of use - specific nature of the antimicrobial agent - physical conditions of the surface to be treated - presence of organic matter - intrinsic characteristics and burden of microorganisms present or suspected - concentration of chemical - duration of contact - temperature - pH - relative humidity.

TABLE II

Comparison of properties of various surface-active agents

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TABLE III

Factors affecting the activity of disinfectants (18)

Disinfectant pH

Factors affecting activity

Organic Water Use against matter hardness bacterial spores

Phenols + ± ± Spores resistant Acids + + ± Alkalis + + + Chlorine-releasing compounds + + ± Sporicidal Iodine compounds + + + Sporicidal Quaternary ammonium compounds + + + Spores resistant Chlorhexidine + + + Spores resistant Glutaraldehyde + Sporicidal Formaldehyde solution - + Sporicidal Alcohols - + Spores resistant Hydrogen peroxide - + Sporicidal Ethylene oxide - + Sporicidal Formaldehyde vapour - + Sporicidal ß-propiolactone - + Sporicidal Methyl bromide - + * all agents are active against most types of non-sporulating bacteria, although activity against mycobacteria may vary

+ influenced ± activity of individual members of a group influenced to varying extents

- not influenced ? little effect

All published reviews on disinfectants recall the desired characterist ics of an antimicrobial product, as follows:

a) rapidly toxic to a wide range of microorganisms at room temperature b) unaffected by envi ronmenta l factors (e.g. organic matter , soap and other

detergents, pH and relative humidity) c) without harmful effects on animals and humans d) non-corrosive e) stable when concentrated or diluted f) soluble in water and unaffected by hard water g) odourless h) cheap, readily-available and easy to use i) able to penetrate and develop a detergent action.

Russel and Hugo (18) summarise the most widely-used disinfectants in veterinary practice and the factors affecting their activity (Tables III and IV) . All personnel involved in the prophylaxis of transmissible infections of animals should be acquainted with this fundamental information.

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TABLE I V

Disinfectants most widely employed in veterinary medicine (18)

Disinfectant type Veterinary uses

Phenols

Acids Citric acid Lactic acid

Formic and propionic acids Hydrochloric acid

Alkalis Lime

Sodium carbonate

Chlorine-releasing compounds

Iodine compounds (iodophors)

Quaternary ammonium compounds

Biguanides (Chlorhexidine)

Aldehydes Glutaraldehyde Formaldehyde solution

Alcohols

Heavy metals

Hydrogen peroxide

Vapour-phase agents Ethylene oxide Formaldehyde Propylene oxide

Widely used as general disinfectants; disinfection of individual pens; wheel or foot dips

Approved for use against foot and mouth disease virus Aerial disinfectant; terminal decontaminant in slaughter and processing procedures Controlling salmonellae in feedstuffs Disinfection of hides and skin contaminated with anthrax spores

Disinfection of livestock pens; white-washing surfaces Cleansing agent

Disinfection of farm buildings and transport vehicles; disinfection of sheep and goat skins

Dairy industry; skin and wound disinfection; veterinary antiseptic; disinfectant; teat dip

Disinfection of automatic calf feeders; incorporation into sheep dips

Application to teats after milking

Disinfection of utensils and premises General farm disinfectant; approved for use against foot and mouth disease and swine vesicular disease viruses; transport vehicles

Skin disinfectants

Copper sulphate as feed additive and (mixed with tar) as topical treatment of foot rot

Disinfection of tools, utensils and premises

Decontaminating agent; steriliser; fumigation of eggshells Fumigant in poultry science For production of contaminant-free animal feeds

SPECIFIC PROCEDURES FOR AIRCRAFT AND SHIP DISINFECTION

The following basic matters must be considered for ship and aircraft disinfection (9,16):

- Cleaning and disinfection should be performed regularly after every shipment of animals, animal products or foodstuffs.

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- Veterinary authori t ies should advise of the type of chemical products and procedures to be used, and perform checks on the execution and efficacy of the disinfection procedure.

- When some danger (e.g. death of animals during the shipment) or epidemic is suspected, veter inary authori t ies should s t rengthen the cleaning and disinfection procedures , de te rmine part icular actions to be taken and select products able to neutralise the specific suspected pathogen.

- Animals generally remain in aircraft for only a short t ime, and the planning of cleaning and disinfection procedures may therefore be difficult.

- In the airport, a specific, separated area should be set aside for use as a quarantine station in case of a suspected epidemic.

- Pens, platforms, bridges and gangplanks should be cleaned and disinfected, together with any other area used for carrying animals and foodstuffs.

The routine procedures may be summarised as follows (2,9,14):

a) Remove gross dirt, straw, hay, food and loose litter. If possible, these materials should be burned; otherwise they should be treated (for at least one week) with one of the following disinfecting solutions: sodium hydroxide 2 % , sodium carbonate 4 % , formaldehyde 1% or cresylic solution 4%. The materials should then be removed and buried.

b) Wooden or plastic materials, ropes, brushes, chains and blankets should be soaked in one of the above solutions.

c) Wash the surfaces with a suitable detergent solution.

d) Fumigate after estimation of the volume. The least expensive and most active product is formaldehyde. Ethylene oxide and glutaraldehyde are effective but are more difficult to use and more expensive. Great care should be taken to protect personnel against exposure to fumigation products , and the premises should be meticulously sealed during fumigation. For every 25 m 3 of space to be fumigated, 1,000 ml of 40% formaldehyde solution and 650 g of potassium permanganate should be mixed in an open metallic container. The gas should be allowed to act for at least 10 h before the enclosure is opened. The temperature of the room must exceed 16°C. Formaldehyde is most effective in moist air and the relative humidity should be > 60%. Alternatively, the gas can be generated by heating paraformaldehyde in an electrically-heated pan or by using an aerosol generator filled with formalin. After fumigation, thorough ventilation is necessary before entry of personnel and animals.

e) Alternatively, chemical disinfection can be performed in a shor ter t ime by spraying or wetting with a disinfectant solution. The disinfectants most widely used in veterinary practice (due to their action against a wide variety of the most pathogenic microorganisms) are listed in Table V.

f) After chemical disinfection, the areas treated should be cleaned (preferably using high-pressure water) to remove any residue.

CONCLUSION

Shipment of animals by sea or air represents a disease threat , due to the possible diffusion of pathogenic agents (mainly exotic viruses, bacteria or parasites).

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TABLE V

Chemical disinfectants useful for disinfection of ships and aircraft

Disinfectant Range of activity Cautions

Sodium hydroxide 2-4%

Sodium orthophenylphenate 4%

Vegetative cells, bacterial spores, many viruses (e.g. FMDV, HCV, SVDV)

Vegetative cells, fungi

Caustic; causes irritation to the skin, eyes and respiratory system; must not be mixed with other products or used on painted surfaces (removes paint)

Mildly caustic and irritating to the skin; must be used at a temperature of >30°C to ensure effective disinfection

Phenolic compounds (cresylic solution 3-4%)

Vegetative cells, acid-fast bacteria, some enveloped viruses

The undiluted product is very irritating to the skin and should be used with caution

Sodium carbonate (soda ash) 2-4%

Sodium hypochlorite 1%

Formaldehyde 2% Glutaraldeyde 2%

Amphoteric agent solution 1-2%

Vegetative cells, some viruses (e.g. FMDV)

Vegetative cells, fungal and bacterial spores, acid-fast bacteria, rickettsiae, chlamydiae, some viruses

Vegetative cells, acid-fast, bacterial spores, rickettsiae, chlamydiae, some viruses

Vegetative cells, G+ bacteria, fungi, some enveloped viruses

Surface-active compounds (quaternary ammonium compounds)

Mixture of peroxide surface-active compounds and organic acids

Vegetative cells, G+ bacteria, fungistatic, some enveloped viruses

Vegetative cells, G+ and G- bacteria, fungi, some viruses

Mildly irritating to the skin; water temperature must be >35°C to ensure crystals go into solution; mainly used for disinfection of vehicles, but will remove some types of paint

Causes irritation to the skin, eyes and respiratory system; rapidly neutralised by organic matter; unstable when diluted

Toxic; causes irritation to the skin, eyes and respiratory system; may be mutagenic

Non-toxic; non-corrosive for materials; can be used as solution with water or alcohol mainly for disinfection of porous surfaces (plywood, cardboard, wood); sporicidal if used at 5% concentration and 60°C

Non-toxic; not harmful to tissue; incompatible with wide range of anionic surfactants (soaps)

Non-toxic; non-corrosive for materials; must be associated with surface-active substances

FMDV: HCV:

SVDV: G+A

foot and mouth disease virus hog cholera virus swine vesicular disease virus Gram-positive/-negative

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If an appropriate and suitable cleaning procedure is followed, this can be effective in removing at least 90% of microorganisms.

Chemical disinfectants should be officially approved by national authorities for use as general purpose disinfectants, or for use against specific groups of pa thogens (e.g. mycobacteria, foot and mouth disease virus, swine vesicular virus, spore-forming bacteria).

Chemical disinfectants are corrosive and harmful to living tissue, and safety measures must therefore be applied to protect workers and animals.

Veterinary authorities must plan the cleaning and disinfection procedures, and must be aware of the efficacy, danger and cost of using the various products and equipment available for fumigation, aerosolisation and wetting of internal surfaces and platforms on ships and aircraft.

* *

LA DÉSINFECTION DANS LES AVIONS ET LES BATEAUX. - EM. Cancellotti.

Résumé : Le transport par avion et bateau d'animaux, de produits d'origine animale et de produits alimentaires est d'une grande importance pour l'économie, mais le risque de transmission d'agents pathogènes représente un réel danger, même si des contrôles vétérinaires sont effectués en permanence.

Bactéries, virus, champignons et parasites excrétés par les animaux contaminent les surfaces et se trouvent à l'abri dans les matières organiques.

Le nettoyage se révèle une étape fondamentale dans les processus de désinfection et, s'il est correctement réalisé, il peut éliminer plus de 90 % des micro-organismes.

Les désinfectants d'origine chimique doivent être compatibles avec les opérations préalables de nettoyage et avec les instruments et les matériaux utilisés ; ils doivent également être sans danger pour les hommes et les animaux.

L'auteur décrit les opérations de base ainsi que leurs principes fondamentaux.

MOTS-CLÉS : Contamination de surfaces - Désinfection chimique -Excrétion de micro-organismes - Nettoyage - Stress - Transport.

* *

LA DESINFECCIÓN EN AVIONES Y BARCOS. - EM. Cancellotti.

Resumen: El transporte por mar y aire de animales, productos pecuarios y productos alimenticios es económicamente importante, pero también representa un verdadero peligro de transmisión de agentes patógenos, incluso cuando los controles veterinarios son realizados de modo permanente.

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Bacterias, virus, hongos y parásitos excretados por los animales pueden contaminar las superficies y son protegidos por la materia orgánica.

La limpieza es un importante paso en el proceso de desinfección y, cuando está bien hecha, puede eliminar más del 90% de los microorganismos.

Los desinfectantes químicos deben ser compatibles con los procesos de limpieza previos y con los instrumentos y materiales utilizados, y deben ser inofensivos para el hombre y los animales.

El autor describe los procedimientos básicos y los principios fundamentales.

PALABRAS CLAVE: Contaminación de superficies - Desinfección química - Estrés - Excreción de microorganismos - Limpieza - Transporte.

REFERENCES

1. ADAMS D.B. (1994). - Transportation of animals and welfare. In Animal welfare and Veterinary Services (R. Moss, ed.). Rev. sci. tech. Off. int. Epiz., 13 (1), 153-169.

2. ANON. (1976). - Emergency animal disease eradication guide. United States Department of Agriculture, Animal and Plant Health Inspection Service, Veterinary Services, Washington, D C , 91-97.

3. ANON. (1991). - Protection of animals during transport. European Community Directive 91/628/EEC, 19 November. Council of the European Communities, Brussels, 11 pp.

4. ANON. (1992). - International Air Transport Association (IATA) Live Animals Regulations, 19th Ed. IATA, Montreal, Canada, 234 pp.

5. ANON. (1993). - Animal Health Act 1981. Chapter 22. Her Majesty's Stationery Office, London, 1-63.

6. ANON. (1993). - Desinfektionsmittelliste der Deutschen Veterinärmedizinischen Gesellshaft (DVG) für die Tierhaltung. Dt. Tierärztebl., 41 (special issue), 8 pp.

7. BELOIAN A. (1990). - Disinfectants. In Official methods of analysis of the AOAC [Association of Official Analytical Chemists], 15th Ed. ( K . Helrich, ed.). AOAC Inc., Arlington, 133-146.

8. CANCELLOTTI EM. (1986). - Disinfezioni: basi razionali e metodi di impiego per la lotta contro le malattie trasmissibili. Selez. vet., 17 (4), 813-835.

9. HILDEBRANDT K . (1982). - Desinfecktionsprobleme bei Lufttransporten von Tieren. Dt. tierärztl. Wschr., 89 (4), 150-152.

10. H U G O W.B. & RUSSELL A.D. (1982). - Types of antimicrobial agents. In Principles and practice of disinfection, preservation and sterilisation, 1st Ed. (A.D. Russell, W.B. Hugo & G.A.J. Ayliffe, eds). Blackwell Scientific Publications, Oxford, 8-106.

11. KELLAR J.A. (1993). - The application of risk analysis to international trade in animals and animal products. In Risk analysis, animal health and trade (R.S. Morley, ed.). Rev. sci. tech. Off. int. Epiz., 12 (4), 1023-1044.

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12. LINTON A.H. (1987). - Epidemiology of infectious diseases in animals. In Disinfection in veterinary and farm animal practice (A.H. Linton, W.B. Hugo & A.D. Russell, eds). Blackwell Scientific Publications, Oxford, 1-11.

13. MARANGON S., FACCHIN E., MONTOU F., MASSIRIO I., VINCENZI G. & DAVIES G. (1994). -The 1993 Italian foot and mouth disease epidemic: epidemiological features of the four outbreaks identified in Verona province (Veneto region). Vet. Rec., 135 (3), 53-57.

14. M O R G A N - J O N E S S. (1987). - Practical aspects of disinfection and infection control. In Disinfection in veterinary and farm animal practice (A.H. Linton, W.B. Hugo & A.D. Russell, eds). Blackwell Scientific Publications, Oxford, 144-167.

15. Moss R. (1994). - International transport of animals: problems relating to disease, welfare and stress. In Animal welfare and Veterinary Services (R. Moss, ed.). Rev. Sci. tech. Off. int. Epiz., 13 (1), 31-41.

16. OFFICE INTERNATIONAL DES EPIZOOTIES (OIE) (1992). - International Animal Health Code: mammals, birds and bees, 6th Ed. OIE, Paris, 550 pp.

17. PHILLIPS J.E. (1987). - Physical methods of veterinary disinfection and sterilisation. In Disinfection in veterinary and farm animal practice (A.H. Linton, W.B. Hugo & A.D. Russell, eds). Blackwell Scientific Publications, Oxford, 117-143.

18. RUSSELL A.D. & H U G O W.B. (1987). - Chemical disinfectants. In Disinfection in veterinary and farm animal practice (A.H. Linton, W.B. Hugo & A.D. Russell, eds). Blackwell Scientific Publications, Oxford, 12-42.

19. SPRINGTHORPE V.S. & SATTAR S.A. (1990). - Chemical disinfection of virus-contaminated surfaces. Crit. Rev. environ. Control, 20,169-229.

20. UNDERWOOD E. (1982). - Good manufacturing practice. In Principles and practice of disinfection, preservation and sterilisation, 1st Ed. (A.D. Russell, W.B. Hugo & G.A.J. Ayliffe, eds). Blackwell Scientific Publications, Oxford, 221-243.