Rev. sci. tech. Off. int. Epiz., 1995,14 (2), 435-445

Inactivation of viruses in liquid manure B. HAAS *, R. AHL *, R. BÖHM ** and D. STRAUCH **

Summary: The stability of some viruses and methods of virus inactivation in liquid manure are reviewed. The authors discuss experimental data on the stability of foot and mouth disease virus, classical swine fever virus, Aujeszky's disease virus, African swine fever virus, swine influenza virus, porcine paramyxovirus, bovine virus diarrhoea virus and transmissible gastroenteritis of pigs virus. Recommendations and practical advice are given for the choice and application of chemical disinfectants for slurry. KEYWORDS: Disinfectants - Liquid manure - Virus inactivation - Virus stability.

INTRODUCTION The causative agents of nearly all bacterial and viral diseases are shed by infected animals in either faeces or urine or by other means. Most of this infective material collects on the floor and thus in t h e m a n u r e (27, 28). Consequently, m a n u r e has a potential for spreading infectious diseases. ' F a r m y a r d m a n u r e ' is a mixture of excreta and substantial quantities of bedding material, and is sufficiently dense to be handled as a solid. 'Liquid m a n u r e ' or 'slurry', however, is a mixture of faeces and urine which may also contain cleaning and rain water, together with small quantities of bedding material and feed, and must therefore be handled in a somewhat different manner. In the past, dung pits filled with farmyard m a n u r e g e n e r a t e d t e m p e r a t u r e s sufficiently high to destroy pathogens. A t present, farmyard m a n u r e often contains insufficient bedding material, and the faeces of modern high performance animals seem to differ significantly in composition and structure from those of farm animals reared at the beginning of the 20th century. Thus, thermophilic microbiological processes can no longer be g u a r a n t e e d to develop during storage of dung. However, the addition of granulated quicklime can still ensure reliable disinfection (3,19,23,26). By contrast, slurry does not normally generate the type of self-heating processes which could destroy pathogens. Thus, after an outbreak of a notifiable disease, slurry must be disinfected by other m e a n s (13, 16, 28). Disinfection of liquid m a n u r e is generally considered to be difficult. In many cases, no a t t e m p t is m a d e to achieve disinfection, as this is considered almost impossible under practical conditions. However, most notifiable diseases could possibly be spread by liquid manure, and it is therefore * Bundesforschungsanstalt für Viruskrankheiten der Tiere, Paul-Ehrlich-Straße 28,72076 Tübingen, Germany. ** Universität Hohenheim, Institut für Tiermedizin und Tierhygiene, Garbenstraße 30,70599 Stuttgart, Germany.

436 i m p o r t a n t to treat slurry after such a disease outbreak. Several chemicals can be considered effective and relatively innocuous to the environment (25). Making decisions regarding the treatment of contaminated slurry requires knowledge of the stability of viruses in liquid m a n u r e , as well as of the capabilities and limitations of chemical disinfectants. Inactivation of viruses in liquid manure by physical or biological means is also possible, but is often impractical due to the lack of suitable equipment.

STABILITY OF VIRUSES IN LIQUID MANURE: EXPERIMENTAL DATA AND OPEN QUESTIONS Very little information is available on the survival times of viruses in farm effluents. Some viruses may survive in faeces of various kinds, d e p e n d i n g on seasonal t e m p e r a t u r e . According to Müller (17), Aujeszky's disease virus may survive for 3-15 weeks, Borna disease virus for 22 days, Marek's disease virus for 7 days, Teschen disease virus for 3-25 days, African swine fever virus for 60-100 days, and foot and mouth disease virus for 21-103 days. However, under practical conditions, survival time is strongly dependent on temperature, p H value and the initial burden of pathogens. B 0 t n e r (5) investigated the inactivation of viruses in slurry at various t e m p e r a t u r e s between 5°C and 55°C, and found a strong temperature dependence of survival time for several viruses (Table I). In a n o t h e r set of experiments (C. E i z e n b e r g e r et al, unpublished findings), the emphasis was placed on the long-term survival of agents of notifiable diseases under simulated field conditions. Classical swine fever virus survived in pig slurry for at least 70 days at 17°C, and for 84 days at 4°C. African swine fever virus survived for at least 84 days at 17°C, and for 112 days at 4°C. Foot and mouth disease virus survived in bovine slurry for at least 70 days at 17°C, and for 84 days at 4°C (Tables II, III and IV). T h e risk of infection associated with the spreading of slurry on farmland cannot be clearly estimated, and therefore the safest procedure is to attempt the best possible d e c o n t a m i n a t i o n of infected slurry before spreading. To achieve a b e t t e r risk assessment, the decimal reduction time (T90) for given pathogens under specific storage conditions should b e investigated further and used to calculate the necessary inactivation time (9). However, B0tner (6) reported a fast initial drop of Aujeszky's disease virus titres compared to the rate of inactivation during the rest of the observation period, and thus concluded that inactivation of Aujeszky's disease virus does not follow first-order kinetics. D a t a r e p o r t e d by various a u t h o r s on virus inactivation in slurry are not easily c o m p a r e d , due to the lack of generally-accepted s t a n d a r d m e t h o d s for this type of experiment. Different conditions in the slurry, and different methods for virus spiking, reisolation and detection, may lead to different inactivation rates. To avoid problems with the adsorption of virus to solid slurry particles and the quantitative elution of these particles, several a u t h o r s used plastic carriers to which virus was adsorbed (20; C. Eizenberger et al, unpublished findings). By contrast, B 0 t n e r (6) mixed the viruses with slurry and reisolated them from the supernatant. Whereas Mack et al. (15) found it necessary to include an elution with beef extract to reisolate more than 12% of Aujeszky's disease virus, B0tner (6) reported a reisolation rate for this virus of up to 100% by addition of 10% f e t a l calf serum to the adsorption m e d i u m . D u e to cytotoxicity of non-centrifuged slurry/virus mixtures, supernatants from centrifuged

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Survival of classical swine fever virus in pig slurry at various temperatures (C. Eizenberger et al, unpublished findings) Titre at 4°C * Day 0 14 28 42 56 70 84 98 112 126

Titre at 17°C *

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7.0 5.5 4.5 4.25 3.75 2.75 4 days; also suitable for use at temperatures between 0 and -10°C. 2

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- N a O H (sodium hydroxide): 5 0 % , 16-30 1/m , exposure time > 4 days; p H > 12; also suitable for use at temperatures between 0 and +10°C. 3

- Formalin: 35-37% solution of formaldehyde in water, 25-401/m , exposure time > 4 days; not suitable at temperatures below +10°C; efficacy reduced below +20°C. 3

- Peracetic acid: 25-401/m , exposure time > 1 h; only suitable in special situations, due to strong formation of foam; also suitable for use between 0 and +10°C. The incubation time of 4 days requested in the regulations should be considered the absolute minimum, and exposure for 7 days would be more advisable.

443

INACTIVATION DES VIRUS DANS LE PURIN. - B. Haas, R. Ahl, R. Böhm et D. Strauch. Résumé : Les auteurs traitent de la stabilité de certains virus et des méthodes d'inactivation de ces virus dans le purin. Ils examinent les données expérimentales concernant la stabilité des virus de la fièvre aphteuse, de la peste porcine classique, de la maladie d'Aujeszky, de la peste porcine africaine, de la grippe porcine, de la paramyxovirose porcine, de la diarrhée virale bovine et de la gastro-entérite transmissible du porc. Les auteurs font des recommandations et donnent quelques conseils pratiques concernant le choix et l'application des désinfectants chimiques des lisiers. MOTS-CLÉS : Désinfectants - Inactivation des virus - Purin - Stabilité des virus.

* * * INACTIVACIÓN DE LOS VIRUS EN EL ESTIÉRCOL LICUADO. - B. Haas, R. Ahl, R. Böhm y D. Strauch. Resumen: Los autores se refieren a la estabilidad de ciertos virus y a los métodos de inactivación de estos virus en el estiércol licuado. Examinan datos experimentales acerca de la estabilidad de los virus de la fiebre aftosa, de la peste porcina clásica, de la enfermedad de Aujeszky, de la peste porcina africana, de la gripe porcina, de la paramixovirosis porcina, de la diarrea viral bovina y de la gastroenteritis transmisible del cerdo. Por último, proponen recomendaciones y criterios prácticos para elegir los desinfectantes químicos y aplicarlos al estiércol licuado. PALABRAS CLAVE: Desinfectantes - Estabilidad de los virus - Estiércol licuado - Inactivación de los virus. *

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