Prof. Dr Reinhard Böhm,
Institute for Environmental and Animal Hygiene and Veterinary Medicine
University of Hohenheim
Stuttgart, Germany
For several bacterial, viral and fungal pathogens survival in the environment is an important factor in epidemiology while for others this does not apply. Those agents, which are transmitted by faecal - oral way, are generally more or less stable in the environment and with some limitations the same applies to those being transmitted via aerosol.
Concerning bacterial pathogens except sporeformers and mycobacteria Salmonella spp. are the group reported to have the longest survival times in faecal media and on surfaces but not in the airborne stage. Even Campylobacter spp. have also the faecal - oral way of transmission they are reported to survive only short times in dry environment. For Pasteurella spp. survival times of several months can be found in the literature. Mycobacterium avium has been reported to survive up to 2 years in the environment; Clamydia psittacii survives depending from the moisture content the temperature and the kind of matrix between 4 and 272 days.
Within the viral pathogens the Newcastle disease (ND) - virus and the influenza A - virus (AI) are mainly in focus of reflections about transmission via inanimate vectors. Depending on moisture, temperature and matrix - virus survives between 30 and 123 days in the environment. Concerning the AI - virus it has been reported that it is infective over 1 month in faeces.
From the other types of viruses the agent of Marek's disease remains infective between 3 days and 8 months depending on environmental conditions and kind of matrix. The ILT - virus can persist between 3 days and 3 months. Poxviruses of birds are found to survive for years in dried organic debris.
Introduction
Transmission via environment is of importance for the epidemiology of several emerging poultry diseases. Those pathways may run via soil, surfaces, manure, water and air and the involved agents may be bacteria, fungi, viruses and parasites. This contribution will not deal with parasites and fungi will be mentioned only without going into further details. One of the most important prerequisites for all the above-mentioned ways of transmission is a sufficient survival time in those environmental compartments. On the other side knowledge on "natural" inactivation may be helpful in risk assessment and prevention.
General factors influencing the survival in the environment
Survival times of pathogens and other microorganisms are determined on one side by the type of agent as well on species as on strain level and on the other side by the environmental conditions during exposure. With some types of organisms the stage of growth may influence the survival as the metabolic situation (Turpin et al. 1993; Foster and Spector, 1995).
In several environments propagation may interfere with starvation, in such cases the epidemiological risks may rise. From the epidemiological point of view survival in the environment can be an important factor for broad host pathogens because they are accessible to living vectors and may be thus transmitted over long distances and times. If the influences of the environment shall be regarded first the nature of organic soiling which covers the pathogen is important. This soiling may be related to the source e. g. se- and excreta or it may be the matrix the pathogen persists in. Its influence is in most cases more or less protecting but sometimes it leads to rapid inactivation (Von Dossow, 1990).
On surfaces in addition survival is influenced by moisture content, temperature, irradiation and type of surfaces (Opara et al. 1992). In soil the moisture and the temperature as well as the type of soil and its pH – value are the main determinative factors, as additional factors antibiosis and availability of nutrients have to be considered for certain pathogens. In manure the temperature, the water content, the pH –value the type of manure and its origin in relation to nutrient content and dissolved gaseous components are mainly influencing the survival times, as for soil the influence of additional biological factors related to the indigenous flora have to be considered (Strauch, 1991).
Survival in water is mainly related to temperature, chemical composition (natural and anthropogenic dissolved chemicals) but biological factors as natural predatory organisms are important in this environment and dilution apparently thins out the introduced flora (Glaus and Heinemeyer, 1994). Air is not a natural habitat for microorganism but sometimes an important vector for certain pathogens. Airborne organisms except the spores of sporeformers are rapidly inactivated in the aerosol. Temperature and humidity are influencing this process but radiation as well as the so-called " open air factor" are of importance too under open air conditions. Moreover the nature of particle the pathogens are attached to is of general importance for their survival. More details can be taken from Müller and Wieser (1987).
Survival of selected bacterial pathogens
In this connection only Campylobacter spp. Clamydia psittacii, Mycobacterium avium, Pasteurella spp. and Salmonella spp. will be regarded here. From the epidemiological point of view survival and persistence of Salmonella in the environment is of special interest since outbreaks in human populations can often be traced back to poultry flocks or poultry products even if the pathogens had been transmitted via environment and vectors (Köhler, 1993).
Campylobacter jejuni is reduced for 5 log in animal beddings in 6 days at 17°C and in 11 days at 8°C (Genigeorgis et al 1985). Other authors report survival times in faeces up to 30 days (Rolle/Mayr, 1993). In surface water C. jejuni survives 4 weeks at 4°C and 2 - 4 days at 25°C (Blaser et al , 1980).
Clamydia psittacii can be detected in dust, feathers and bedding material after 6 months but seems not to be very stable in pure dried faeces for which survival times of 4 to 30 days are reported (Gylsdorf and Grimm, 1998; Rolle/Mayr, 1993).
In water clamydia psittacii may survive for 17 days.
Mycobacterium avium survives on surfaces in dark environment 10 to 18 months while it is only viable for 7 days on surfaces exposed to sunlight. In faeces and in animal beddings it survives about one year (Schulz, 1992). Contaminated soil in poultry runs has to be regarded as infective for several years, "self decontamination" of such premises cannot be attended before 3 years (Rolle/Mayr, 1993).
Pasteurella multocida survives on surfaces at 12°C - 15°C 7 days at room temperature 5 days. In manure it may survive up to two months. In soil or buried carcasses survival times of up to 30 days are reported (Gylsdorf and Grimm, 1998; Mezzaros, 1992).
A lot of data are reported in the literature concerning the survival of Salmonella ssp. a compilation of such data has been given by Böhm (1993). While survival times on clean metallic surfaces are relatively short (S. Typhimurium 14 days) at 10°C much more longer survival can be expected if the bacteria are protected by dust and stored at room temperature.
Table 1 gives some data (McDade and Hall, 1964; Miura et al., 1964; Enkiri and Alford, 1971).
In liquid poultry manure Salmonella can survive up to about 2 months: Table 2 gives some data collected by Strauch (1987)
In soil survival times between 4 and 56 days had been reported (Tannock and Smith 1972, Platz, 1981). Those data are depending from several factors so even longer persistence in such habitats could be expected. Decimal destruction rates (D - values) for S. Typhimurium in surface water had been reported by Mitchel and Starzyk (1975), they are as follows:
- D0 = 13 d
- D5 = 16 d
- D10 = 8 d
- D 20 = 7 d
The possibility of aerogenic transmission of Salmonella had been reported, but general the survival of gram-negative bacteria in aerosols is short and depends strongly on air humidity. For S. Typhimurium it was found that every minute half of the airborne population is inactivated (Wathes et al., 1988).
Survival of selected viral pathogens
In this connection only the Newcastle Disease (ND) - virus, the Influence A (AI)- virus, the Infectious Laryngotracheitis (ILT) - virus, the Marek's Disease - virus and the Avipox viruses will be regarded.
The ND - virus remains active on surfaces in the environment up to one month, on feathers at 20°C for 123 days, in moist soil for 22 days and in lake water for 19 days (Boyd and Hanson, 1958: Moses et al. 1947; Olesink, 1951; Saber et al., 1968). Also the influence A viruses are enveloped, they are considered relatively stable as ND - virus, particularly in surface water. The virus remains infectious in faeces for over one month. As mentioned above it remains infectious in water for 207 days at 17°C (Stallknecht et al., 1990).
The herpes viruses as those causing ILT or Marek's disease are not surviving very long in the environment on surfaces. They are mostly inactivated in 48 hours in se- and excreta. On the other hand they may survive 3-20 days in the bedding material (Schmidt, 1992). Marek's disease virus has even been found to remain infective for 4 to 8 months if protected in feather debris or faeces at cool temperatures (Calnek and Witter, 1991).
Poxviruses are environmentally stable and can survive for years in dried organic debris such as faeces blood soil or scabs (Andrews et al., 1978; Gerlach, 1994)
Final remarks
The data given here are showing that in most cases systematic research concerning survival of pathogens in the environment are missing. This generates conflicting results since most of the data are based on different experimental conditions or are generated by single case analysis.
Other data e.g concerning the survival of widely spread organisms like Aspergillus fumigatus which are not transmitted from animal to animal via environment but released from certain materials in the environment of the birds are without epidemiological importance. Nevertheless more research is needed but it is nearly impossible to get such research founded in the present situation.
References are available on request
From Proceedings of 11th European Poultry Conference, Bremen, Germany.
