Results
Aerosol viral sampling:
The air collection occurred for 3 hours, beginning at the start of the
grinding process. The grinding was completed at approximately 2.5 hours,
but the aerosol collection at each distance ran for the full 3 hours. An
aerosol sample was collected from each device after every 60min run time
(18 total samples) for PCR testing. All filter elution samples tested
negative for PRRSV and PEDV by PCR. Upon receiving negative virus
results on all samples, filter pads from each collection point were
vortexed with saline, and PCR retesting on the resulting fluid was
attempted to increase testing sensitivity. All samples were PCR negative
for PRRSV on the retest; however, a single PEDV PCR positive sample was
detected in one collector at the 137m (150 yards) distance with 36.55ct
(cut-off used by the lab is 38ct).
Water viral testing:
A water sample collection was attempted on every well weekly. Eleven
total water well samples were able to be attained through the study, as
seen in Table 1. The only positive PCR result was in week five on the
0.15m well under the cornstalks biomass. Successful attempts to collect
water samples were from depths of 0.15m and 0.46m, with no samples
collected from the 0.91m depth.
Compost temperature by treatment and biomass type:
Regardless of compost sections microbial digestion treatment, the piles
achieved similar temperature peaks, as reported in Table 2. By day three
post windrow formation (pwf), each compost type reached an internal
temperature of 60°C or higher and maintained that heat for at least 48
hours except for the treated section of the mixed biomass windrow that
dropped to 55.6°C on day five pwf. Woodchips appeared to reach the
highest peak compost temperature at 75.6°C on day three pwf. Woodchips
and the treated section of the cornstalks reached temperatures
>60°C by day two pwf, a day before the mixed biomass. The
average high air temperature for the first five days pwf when peak
windrow temperatures were met was 3°C and the low was -5.1°C. The only
added moisture to the compost piles from the weather during the first
five days pwf was minimal with 0.05cm of rainfall and 0.51cm of
snowfall.
Compost viral testing:
Day 0 (when the carcass grinding and windrow formation occurred)
revealed PCR positive results for both PEDV and PRRSV in all three
biomass materials. As reported in Table 3, woodchips had a greater
number of samples with PCR positive results for both PRRSV and PEDV
compared to cornstalks and the combination material. Cornstalks compost
provided the least amount of PRRSV and PEDV positive results. Table 3
shows that the last PRRSV positive result was detected on day four pwf
in the woodchips, and PEDV was detected out to week 2 in both the
woodchips and combination piles.
Swine DNA testing:
Swine DNA could be detected in the compost sample of each biomass type
up to five days pwf. As seen in Table 4, at weeks 2 and 3 pwf, swine DNA
could still be detected in each biomass type. Table 5 shows the results
of the swine DNA detection from the air collection during the grinding
process. Only two positive results were detected, occurring at hour 3 in
one collector at the 46m distance and one at the 91m range. No swine DNA
was detected at the 137m distance.
Bioassay:
The PCR positive processed compost was placed into PRRSV and PEDV naive
pigs to assess the infectivity of the virus detected. No PRRSV positive
compost samples replicated to produce a PRRSV positive pig by serum PCR.
Cornstalk biomass was negative for PEDV infection on bioassay. Woodchips
provided the most PCR positive PEDV results by rectal swabs in the
challenged pigs. As seen in Table 6, woodchip compost from day three and
week two and the combination pile compost from week two produced a
single PCR positive pig for PEDV on day four post-challenge, but all
pigs were negative on day seven post-challenge. Clinical signs of
diarrhea consistent with PEDV infection were observed in day 0, 2, and 4
pwf samples from the woodchips with multiple pigs in those pens testing
positive by PCR. In the pen of pigs challenged with the week two
combination biomass, one pig died from unrelated illness before the
first sample collection.