Rabies Virus: Toward Ante-Mortem, Sub-Clinical Diagnosis by Electron Microscopy
By Travis Cobb
According to the Centers for Disease Control and Prevention (CDC), Rabies is the cause of approximately 59,000 deaths annually worldwide. Rabies is 100% fatal and with no approved treatment or survivability upon clinical symptom presentation. With the low-efficacy and general irreproducibility of the “Milwaukee protocol,” post-exposure prophylaxis (PEP) is essential in preventing disease onset through multiple rounds of vaccine alongside rabies immunoglobulin. There remains no single test to diagnose rabies infection sub-clinically in humans, with the gold standard being brain tissue analysis via animal host necropsy.
Electron Microscopy (EM) appears a reliable option for early diagnostics given its ability to image Rhabdoviridae. Limitations include equipment size, expense, and technical expertise essential for operation. This can be partially addressed by the use of the Low-Voltage electron microscope (6-25kV). Such is functionally compact and does not require staining given its enhanced contrast, provided tissue samples are thin enough for examination (20-65nm).
Rabies virus is known to initially replicate in infected muscle tissue of bite wounds. This could be the basis for aforementioned diagnosis via muscle biopsy by simple viral load presence. Combined with EM (having been used in rabies imaging previously), further research is necessary to determine the viability of this approach.