Poliomyelitis, commonly known as polio, is a highly infectious viral disease that primarily targets the human nervous system. This infection can lead to muscle weakness and, in severe cases, permanent paralysis. While polio is widely recognized as a human affliction, the question of whether animals can contract it introduces a layer of complexity crucial for understanding the virus and its control.
Poliovirus and Non-Human Primates
Non-human primates (NHP), particularly chimpanzees and macaques, are uniquely susceptible to human poliovirus infection. They can develop paralytic symptoms similar to humans due to physiological similarities, especially the presence of the poliovirus receptor (PVR), also known as CD155, on their cells. This protein acts as the virus’s entry point, facilitating infection.
Their susceptibility made them invaluable for polio research. Scientists used these animal models to understand how the virus causes disease and to develop effective vaccines. Early 20th-century experiments successfully transmitted polio to monkeys, establishing an important research model. This extensive research significantly contributed to the development of inactivated and oral polio vaccines in the 1950s.
Poliovirus in Other Animals
Common domestic animals like dogs, cats, horses, and cattle, along with most other wildlife, are not susceptible to the human poliovirus. The virus cannot bind to their cells, meaning they do not naturally contract or transmit the human form of the disease. While some animal diseases present with neurological symptoms resembling polio, these are caused by distinct viruses. For example, polioencephalomyelitis in cats or polioencephalomalacia in ruminants cause neurological signs but are not linked to the human poliovirus.
Polioencephalomalacia in ruminants, often called “polio” in veterinary contexts, is a brain disorder caused by thiamine (vitamin B1) metabolism disturbance, not a viral infection. Similarly, various enteroviruses can affect animals, leading to neurological issues, but these differ from the human poliovirus.
Animal Models and Polio Eradication
Understanding animal susceptibility, or its absence, has implications for polio research, vaccine development, and global eradication. Non-human primates played a foundational role as historical animal models, enabling scientists to study poliovirus pathogenesis and test vaccine safety and effectiveness. This research was instrumental in widespread vaccination campaigns that drastically reduced polio cases worldwide.
Knowing that humans are the only natural reservoir for the poliovirus is an important factor in global eradication campaigns. The absence of animal reservoirs means the virus cannot silently circulate in animal populations, making disease elimination feasible through widespread human vaccination. While ethical considerations and alternative laboratory models have reduced reliance on non-human primates for some research, their historical significance in overcoming polio remains undeniable.