China Veterinary Diagnostic Techniques for BPIV3 and CPIC3

China veterinary diagnostic techniques for detecting bovine and caprine paramyxovirus type 3 (BPIV3 and CPIV3) infections have been published by the National Technical Standardization Committee of Animal Health on October 9, 2024. This standard, titled "Diagnostic Techniques for Bovine and Caprine Parainfluenza Virus Type 3" and numbered GB/T 44613-2024, outlines comprehensive diagnostic methodologies designed to enhance the accuracy of diagnosing these viral infections in cattle and goats. The new standard is set to take effect on April 1, 2025, and plays a crucial role in supporting the livestock industry, particularly for veterinary diagnostic manufacturers and regulatory affairs managers operating in China.

Overview of GB/T 44613-2024

The standard includes methods for clinical diagnosis, virus isolation, RT-PCR, real-time PCR, competitive enzyme-linked immunosorbent assay (cELISA), and virus neutralization tests (VNT). These techniques are applicable for diagnosing and detecting infections caused by BPIV3 in cattle and CPIV3 in goats and sheep. Both BPIV3 and CPIV3 are respiratory viruses that affect livestock and can lead to significant economic losses in the agriculture industry due to reduced productivity and, in severe cases, mortality. This standard is particularly important for companies that manufacture veterinary diagnostic kits or provide veterinary healthcare solutions, as it offers a structured approach to diagnosing viral infections common in large-scale livestock operations. The focus on both bovine and caprine species highlights the versatility of the standard in addressing multi-species infections.

Key Diagnostic Methods

Clinical Diagnosis

The clinical diagnosis method emphasizes recognizing the epidemiology, clinical symptoms, and necropsy findings associated with BPIV3 and CPIV3 infections. The standard identifies that these infections can occur year-round but are most prevalent in autumn and winter. Environmental stressors, such as sudden weather changes and long-distance transportation of animals, exacerbate the spread of the disease.

Epidemiology: BPIV3 primarily affects cattle but can also infect deer, pigs, and sheep, while CPIV3 mainly targets goats and sheep. Both sick and asymptomatic animals serve as primary sources of infection.
Symptoms: Clinical symptoms include fever, depression, coughing, sneezing, nasal discharge (serous, mucous, or purulent), and breathing difficulties. These symptoms resemble those of other respiratory infections.
Autopsy: Post-mortem examinations often reveal tracheal congestion, bleeding, and proliferative lung consolidation, aiding in posthumous infection identification in suspected cases.

Virus Isolation and Identification

Virus isolation is a critical diagnostic tool outlined in the standard. The process utilizes Madin Darby Bovine Kidney (MDBK) cell cultures to identify the presence of BPIV3 or CPIV3 in swab, serum, or tissue samples. The procedure includes inoculating the samples into the MDBK cell culture, observing the cytopathic effects (CPE) that indicate viral replication, and confirming the viral presence through further testing.

Preparation: After MDBK monolayer cell preparation, virus inoculation, MDBK culture preparation.
Test Procedure: Inoculated cell cultures are monitored for CPE, a typical sign of viral infection, and samples showing these effects are tested further. A negative result is declared if no CPE is observed, while a positive result confirms the presence of the virus.

RT-PCR and Real-time PCR Detection Methods

The standard specifies both conventional RT-PCR (reverse transcription polymerase chain reaction) and real-time PCR (real-time reverse transcription polymerase chain reaction) for detecting viral nucleic acids in cattle and goat samples. These molecular diagnostics are highly sensitive and are essential for confirming infections at early stages or in asymptomatic animals.

RT-PCR: This method amplifies viral RNA to detect the virus in swabs, serum, or tissue samples. Agarose gel electrophoresis is used to visualize amplification products, with specific bands indicating a positive result.
Real-time PCR: This method allows quantitative detection by monitoring the amplification of viral nucleic acids in real-time through fluorescence. The cycle threshold (Ct) value is critical, with lower Ct values indicating higher viral loads. A Ct value of ≤35 and a characteristic amplification curve confirm a positive test result, while samples without a Ct value are considered negative.

cELISA (Competitive enzyme-linked immunosorbent assay)

cELISA detects antibodies to BPIV3 and CPIV3 in bovine and caprine serum, indicating past infections or immune responses in vaccinated animals. The test measures the percentage inhibition (PI), determining if the sample is seropositive or seronegative.

Operation: The test involves adding serum samples to a plate coated with viral antigens and detecting antibody presence by observing competitive inhibition. Samples with a PI greater than 38% (for cattle) or 35% (for goats) are considered seropositive, indicating exposure to the virus.
Importance: cELISA is particularly useful for herd-level monitoring and evaluating the effectiveness of vaccination programs.

Virus Neutralization Test (VNT)

The VNT quantifies neutralizing antibodies in serum samples, providing insights into the immune status of animal post-infection or post-vaccination. This method involves incubating the virus with serum samples and assessing whether the serum can neutralize the virus.

Procedure: The test uses serial dilutions of the serum and evaluates the presence of CPE in MDBK cell cultures. A positive result is indicated by a neutralizing antibody titer of ≥1:4.
Significance: This test is essential for confirming the presence of protective immunity in herds, particularly for vaccinated animals or those previously exposed to the virus.

Implementation and Compliance for Veterinary Manufacturers

Veterinary diagnostic and product manufacturers must ensure their products align with the standards set forth in GB/T 44613-2024. This standard provides a comprehensive and clear framework for testing and diagnosis, which should be incorporated into existing product development and validation protocols. Companies should review and update their diagnostic tools, including PCR kits, ELISA assays, and virus isolation protocols, to meet the stringent requirements of the new standard.

Further information

By staying informed and adapting to these regulatory changes, veterinary drug manufacturers can continue to ensure the safety and efficacy of their products, contributing to improved animal health and public safety. Our Cisema experts are here to guide you through the regulatory landscape in China.

Read the original announcement on Diagnostic Techniques for Bovine and Caprine Parainfluenza Virus Type 3.

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