Discuss the following in about 150 words each: 1.(e) Write about the collection, methods of preservation and dispatch of samples from the carcass of suspected rabid dog for laboratory diagnosis.

1. Collection of Samples from a Suspected Rabid Dog Carcass

The primary tissue required for rabies diagnosis is the brain, specifically sections from the brainstem and cerebellum, as the rabies virus preferentially targets the central nervous system. Strict safety protocols are crucial due to the high risk of exposure to the rabies virus.

• Safety: Personnel involved must be fully vaccinated against rabies, wear appropriate Personal Protective Equipment (PPE) including gloves, masks, and eye protection, and work in a well-ventilated area.
• Procedure: Ideally, the entire head of the suspected rabid dog is carefully removed by trained personnel using sterile instruments. If the whole head cannot be sent, key sections of the brain (cerebrum, cerebellum, brainstem/medulla) should be collected ensuring representative tissue. The occipital foramen approach is a safer method for brain sampling.
• Avoid Freezing (initially): Freezing the entire carcass should generally be avoided before sample collection, as it can damage tissue integrity, although frozen samples can still be tested via PCR if no alternative.

2. Methods of Preservation of Samples

Proper preservation maintains viral integrity and diagnostic accuracy during transit.

• Refrigeration (Short-term): Brain samples should be immediately placed in a robust, leak-proof container (e.g., wide-mouth, screw-cap polypropylene jar) and refrigerated at 4°C. This method is suitable for short-term preservation (up to 48 hours).
• Glycerine Saline (Preferred for Transport): For longer transit times or when refrigeration is inconsistent, brain tissue segments can be immersed in a 50% glycerine-saline solution. This solution acts as a preservative without significantly impacting viral antigen detection.
• Freezing (Long-term/Molecular Tests): For long-term storage or if molecular diagnostic methods like RT-PCR are anticipated, samples can be frozen at -20°C or ideally -80°C. While freezing can affect tissue morphology for some tests, it preserves viral RNA for PCR-based diagnosis. Repeated freeze-thaw cycles should be avoided.

3. Dispatch of Samples for Laboratory Diagnosis

Timely and secure dispatch is critical to expedite diagnosis and initiate public health interventions.

• Packaging: Samples must be packaged according to biohazard transport regulations, typically involving a triple-packaging system:
  1. Primary Container: A leak-proof, screw-cap container holding the brain tissue, sealed properly.
  2. Secondary Container: A durable, leak-proof bag or container enclosing the primary container, often with absorbent material to soak up any leakage.
  3. Outer Packaging: A sturdy, insulated box with appropriate cushioning.
• Temperature Control: Ice packs (not dry ice in direct contact) should be placed in the outer packaging to maintain a cold temperature during transit.
• Labeling: The outer package must be clearly labeled with a biohazard symbol, sender's and receiver's addresses, contact details, and a manifest detailing the contents, animal information (species, date of death, suspected disease), and collection date.
• Timely Transport: Samples should be dispatched as quickly as possible to a certified veterinary diagnostic laboratory, ideally within 24-48 hours, to ensure optimal sample quality for tests like the Direct Fluorescent Antibody (DFA) test, which is the gold standard.