Heat inactivates HPAI virus in poultry litter

Recovery from outbreaks of HPAI requires cleaning and disinfection before premises can be tested to be declared negative for virus.

The U.S. Poultry & Egg Assn. (USPOULTRY) announced the completion of a funded research project at the Athens, Ga., Southeast Poultry Research Laboratory of the U.S. Department of Agriculture's Agricultural Research Service (ARS) in which a researcher provided various time and temperature profiles to effectively inactivate the avian influenza virus in poultry litter.

USPOULTRY approved $550,000 in emergency funding in October 2015 to support further avian influenza research and communication as a result of the 2015 highly pathogenic avian influenza (HPAI) outbreak. USPOULTRY noted that these projects are to be completed on a fast track over the next several months, and this research is the second project completed with the funding.

During an HPAI outbreak, a great deal of time and effort goes into attempting to inactivate avian influenza virus in a contaminated facility using cleaning and disinfection.

ARS researcher Dr. Erica Spackman showed that the HPAI virus can be inactivated relatively quickly by heat, and she established the parameters required to achieve inactivation of the virus. This is important information that can be used in future outbreaks to more quickly eliminate the virus from inside contaminated facilities, USPOULTRY said.

Recovery from outbreaks of HPAI requires cleaning and disinfection before a premises can be tested to subsequently be declared negative for virus. Cleaning and disinfection have focused on removing all organic material, require extensive labor and time and are expensive procedures. Since the avian influenza virus is not environmentally stable and can be inactivated at high temperatures, an alternative to complete removal of organic material is to use heat to kill the virus, Spackman said. Using heat to reduce the environmental load of the virus will also improve safety for individuals involved in recovery at infected premises.

Therefore, the objective of this work was to determine the time necessary to inactivate avian influenza virus in poultry litter at different temperatures.

Low-pathogenic avian influenza virus (LPAI) was evaluated at eight temperatures in 10°F increments and in both high-moisture and low-moisture litter. The environmental stability of LPAI and HPAI are expected to be the same based on other inactivation studies, Spackman noted. However, as confirmation under these conditions, HPAI was tested, but at 20°F increments.

Virus of a known titer was added to specific volumes of wet litter (taken from the area under the drinkers) or dry litter from a specific pathogen-free chicken flock. The litter material was kiln-dried, medium-flake wood shavings. Each set of LPAI-spiked dry and wet litter was incubated at 50, 60, 70, 80, 90, 100, 110 and 120°F. Samples were taken daily and were tested for the quantity of viable virus present by titration in embryonating chicken eggs. Tests with HPAI virus were conducted identically, except only at incubation temperatures of 50, 70, 90 and 110°F.

Spackman explained that ranges of temperatures and moisture levels were used to simulate what may be present in the field and what maximum temperatures can be achieved in different regions. Results are shown in the Table.

According to Spackman, there was some variability at the lower temperatures, which was expected. Because of the variability, the longest observed inactivation times for 60°F and 50°F (i.e., five days) should be used in the field. An additional 24 hours should be added to this and each time point as an added measure of safety, Spackman suggested.

In addition, the heat-treated samples were also tested by real-time polymerase chain reaction (RT-PCR) to determine the rate of RNA decay relative to virus isolation. The practical application is that if the RNA breakdown is similar to inactivation, then RT-PCR could be used to test environmental samples instead of virus isolation to save time. Unfortunately, even at the higher temperatures, the endpoints for RT-PCR were beyond those for virus isolation. Therefore, virus isolation will be more reliable, Spackman said.

These data provide guidelines for the minimum times necessary to inactivate avian influenza virus at a given temperature. In an outbreak situation, a poultry house should be heated to the highest temperature that is practical and for the longest time practical. Importantly, the temperature of the litter must be monitored throughout the process to verify treatment, Spackman concluded. Since inactivation is a function of temperature, virus on other surfaces and in other litter types are expected to be inactivated under the same thermal conditions.

Days to inactivate LPAI and HPAI by temperature and moisture level. Inactivation was considered complete when all three replicates were negative.

Virus

Moisture

120°F

110°F

100°F

90°F

80°F

70°F

60°F

50°F

LPAI

Wet

1

1

1

1

1

2

4

5

 

Dry

1

1

1

1

1

2

5

4

HPAI

Wet

1

1

2

3

 

Dry

1

1

2

5

Recommended time*

 

2

2

2

2

2

3

6

6

*The recommended time is the minimum number of days that should be implemented at a target temperature in the field.

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