Microbial pathogen survival study in a high plains feedyard playa.

Abstract. -- Sixteen microbes and one enteric protozoal parasite were secured in screw-cap vials (CV) and dialysis tubes (DT) and placed in a feedyard shallow lake (playa) in the West Texas High Plains, USA. They were removed weekly or monthly depending on their susceptibility to the water environment. There were two overlapping studies; one started in September 1996 and was terminated 390 days later. The second study started in May 1997 and was terminated 188 days later. These controlled studies were used to determine the decrease in titers of 10 bacteria (Pasteurella haemolytica A1, Pasteurella multocida A:3, Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, Actinomyces pyogenes, Salmonella enterica serovar dublin, Bacillus thuringiensis, Klebsiella pneumoniae and Pseudomonas aeruginosa); two fungi (Aspergillus fumigatus and Aspergillus niger); four viruses (Infectious Bovine Rhinotracheaitis (IBR), Bovine Virus Diarrhea Virus (BVD), Bovine Respiratory Syncytial Virus (BRSV), Bovine Parvovirus (BPV) and one protozoal parasite (Cryptosporidium parvum), over time. The Pasteurella isolates died in both studies within seven to 35 days. Actinomyces pyogenes died within 84 days in the 1996 study and survived for 188 days in the 1997 study. The remaining bacterial isolates in 1996 survived for 390 days with low titers, except for P. aeruginosa. Both fungal isolates died by 390 days in the 1996 study. All bacteria and fungi survived the 188 day study in 1997, except for the Pasteurella isolates. The titers of the viruses decreased rapidly over 42 days, except for BPV in the 1996 study, and all viruses were inactivated by day 42 in the 1997 study. Cryptosporidium parvum survived the 1996 winter but lost its ability to infect infant mice during the month of May, 1997. Microbial survival decreased more rapidly in DT samples compared to CV samples.

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Feedyards with large numbers of calves (25,000 to 100,000 head) are becoming more highly regulated by state and federal governments than in the past regarding their suspected contribution to contamination of the air (Elbers et al. 1996), soil (Faust 1982) and water (Evans & Owens 1972; Miner et al. 1967; Miner et al. 1996). There are many studies which relate to soil and water contamination by manure (Crane et al. 1983; Diesch 1975). More than 20 diseases have been identified as possibly transferred from animal manure (Azevado & Stout 1974). Manure contamination from dairy (Jansen et al. 1974; Rankin & Taylor 1969) and swine operations are frequently called point source pollution. This pollution often consists of nitrate contamination of storm water runoff which can severely impact animal life and vegetation in streams and rivers (McLead & Hegg 1984; Power & Schepers 1989). The effects of this contamination are compounded by rapid algal-blooms (Alexander 1974). One paper has examined feedyard nitrate contamination in the Texas High Plains of the United States (Stewart et al. 1967).

Water quality is also frequently decreased by contamination from fecal coliforms, Enterococcus faecalis, Klebsiella pneumoniae, Pseudomonas aeruginosa and Salmonella due to point source pollution (Geldreich 1969; Geldreich & Kenner 1969; Yanko et al. 1995) and non-point source pollution (Beyer & Perry 1987; Doran & Linn 1979; Doran et al. 1981; Green & Crawford 1990; Pasquarell & Boyer 1995; Thelin & Gifford 1983). In arid areas, waste water becomes a precious commodity and it is frequently used for irrigating crop vegetation and in the production of compost. It is of interest to know how long the pathogens in the waste water will survive on vegetation (Bell 1976; Findlay 1972; Tannock & Smith 1971).

Several studies have addressed the issue of pathogen contamination and survival in waste water (Clark et al. 1981), treatment plants and their products (Rudolfs et al. 1950a; Rudolfs et al. 1950b; Stewart et al. 1967). Some have examined microbial contamination of the feedyard and its immediate environment (Miner et al. 1966; Miner et al. 1967). There is, however, a paucity of literature concerning feedyard microbial contamination of feedyard lakes. Also, little specific information is available on the survival of microbial pathogens located in or near feedyards of the High Plains (Corrier et al. 1990). Two studies determined aerobic microbial counts from manure in a small midwestern feedyard of 5,000 to 10,000 head (Hrubant et al. 1978; Rhodes & Hrubant 1972).

Microbial loading of the feedyard, air, water and soil in the Texas High Plains of the United States is unknown. It is also unknown how long pathogens survive in nearby shallow lakes (playas) of this area. These playas play an important role in containing runoff from large feedyards, since by their nature they have no effective surface drainage systems. Playas provide a valuable source of water for resident wildlife and for migratory birds passing through the semi-arid southwest Texas High Plains. It has been suggested that water contamination from feedyard runoff is less of a problem in arid than in semi-arid areas (Viets 1971) because of fewer rains. Nevertheless, there is a need to determine how long pathogens might survive in specific environments in order to evaluate the potential risks in using playas as a source of drinking water for wild animals and as a source of water for irrigation purposes of food crops.

This report will focus on the survival of 10 bacteria, two fungi, four viruses and one protozoal parasite over time in a feedyard playa. The study was done in two parts, which overlapped in time. The first was started on 23 September 1996 and concluded 390 days later, and the second was started on 14 May 1997 and concluded 188 days later.

METHODS

Overall design and collection of microbes. -- The design was to place a known titer of 17 different agents in multiple sets of two types of tubes in a typical feedyard playa. Randomly placed duplicate tubes containing the specimens were retrieved at predetermined times and the agents were re-titered to determine decreases over time.

The first tube type was a screw-cap cryro-vial (CV) and the other was a dialysis tube (DT). Multiple tubes of both types were filled with the identified agents and placed in a bucket with numerous holes drilled into the sides and bottom. A lid was attached snugly. The bucket was allowed to fill with water and was submerged to the bottom of the lake (approximately 3 foot depth) with the aid of weights. A line was attached and anchored at the shore line for easy retrieval.

When CV sample tubes were collected from the playa lake they were placed on ice. When collected, the DT were first placed in cold sterile water, then on ice. Sampling during the first study was determined to be more frequent than necessary, therefore, sampling frequency in the second study was reduced. There were two overlapping studies. One started September 1996 (winter), and one started in May 1997 (summer).

At the indicated times, samples in CV and DT were removed from the playa, protected from sunlight, placed on ice and immediately taken to the United States Department of Agriculture laboratory. Exceptions included the viral agents, which were immediately frozen and stored at -85[degrees]C. After the last virus samples were collected, they were all placed on dry ice and delivered to the virus laboratory where they were thawed and titered along with frozen controls which the virus laboratory had retained. There was also a refrigerated control for the parasite sample. After each collection, the parasite samples were placed on ice packs and immediately mailed overnight to the laboratory, where the samples were inoculated by mouth into newborn mice to determine viability and infectivity of the parasites.

Sampling intervals. -- In general, all bacteria and fungi were sampled monthly, except for P. haemolytica and P. multocida which were sampled each week. …