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Relative rates of Aujeszky's disease virus attenuation, as assessed in mice
Abstract:
Field strains of Aujeszky's disease virus (ADV) were attenuated by heat treatment and serial passage at sub-optimal growth temperatures in chicken embryo fibroblasts (CEF). At chosen passage levels, virus was titrated in cell culture and in mice. For each strain, the pathogenicity was expressed as a mouse lethal index (MLI), defined as the inverse of the log10 (CCID50:LD50). MLIs determined for field strains displayed a wide range of comparatively high values. The attenuation of field strains was accompanied by a rapid fall in MLI values, particularly in the initial stages. Heat-treated ADV attenuated faster than untreated ADV, when passaged at 30 degrees C. Passage at 27 degrees C resulted in considerably accelerated attenuation compared to passage at 30 degrees C, in the case of both untreated and heat-treated ADV. MLIs were determined for attenuated ADV strains that had been tested in 6-day-old piglets. Low MLI values were found to correlate with low virulence in piglets and high MLI values with virulence.
Insights
This study attenuated Aujeszky's disease virus (ADV) using heat and low-temperature passage in chicken embryo fibroblasts. Lower temperatures and heat treatment accelerated ADV attenuation, correlating with reduced virulence in piglets.
Area of Science:
- Veterinary Virology
- Animal Disease Research
- Virus Attenuation
Background:
- Aujeszky's disease virus (ADV) poses a significant threat to swine health.
- Attenuating field strains of ADV is crucial for vaccine development and disease control.
- Current attenuation methods require optimization for efficiency and predictability.
Purpose of the Study:
- To investigate the efficacy of heat treatment and serial passage at sub-optimal temperatures for attenuating ADV field strains.
- To evaluate the correlation between a defined mouse lethal index (MLI) and virulence in piglets.
- To identify optimal conditions for accelerated ADV attenuation.
Main Methods:
- Field strains of ADV were subjected to heat treatment and serial passage in chicken embryo fibroblasts (CEF) at 30°C and 27°C.
- Virus pathogenicity was assessed using a mouse lethal index (MLI), calculated as the inverse of log10 (CCID50:LD50).
- Attenuated ADV strains were tested for virulence in 6-day-old piglets.
Main Results:
- Field ADV strains exhibited high initial MLI values, indicating significant pathogenicity.
- Attenuation was rapid, especially during initial passages, leading to a sharp decrease in MLI.
- Heat-treated ADV showed faster attenuation at 30°C compared to untreated strains.
- Passage at 27°C significantly accelerated attenuation for both heat-treated and untreated ADV.
- Low MLI values correlated strongly with low virulence in piglets, while high MLI values indicated virulence.
Conclusions:
- Heat treatment and low-temperature passage (especially 27°C) are effective methods for attenuating ADV field strains.
- The MLI is a reliable indicator of ADV virulence in piglets.
- Optimized attenuation protocols can enhance the development of safer and more effective ADV vaccines.