By Mitali Mehta
Within the complex terrain of human health, the intersection between infectious diseases and neurological outcomes represents a realm often overlooked. Often we compartmentalize diseases into tidy categories, focusing on the primary symptoms while forgetting the possibility of distant effects including those that are neurological in nature. However, what if we told you that several common infections could stealthily impact nerves, causing a range of debilitating neuropathies? Neuropathies represent a lesser-known yet critical facet of infectious diseases.
Imagine recovering from the distress of an infectious bloody diarrhea, only to suddenly find yourself paralyzed, unable to walk, move your hands or legs, or even swallow food. Guillain-Barré syndrome (GBS), is a rare condition in which a person’s immune system attacks their peripheral nerves. During the preceding GI infection, the immune system creates antibodies to fight the causative bacteria, Campylobacter jejuni. But these antibodies travel far from the site of original infection and can end up targeting myelin, the protective sheath around nerves. This immune response against myelin leads to dysfunction of the nerves controlling muscle movement. As a result, individuals with GBS experience muscle weakness often referred to as “Ascending Paralysis” due to its characteristic progression. While more common in adults and males, all individuals can be affected. GBS stands as a quintessential illustration of “parainfectious” neuropathy, wherein the pathogen does not directly infect the nerve, but does precipitate an immunologic phenomenon which can lead to profound neurological consequences.
Infectious pathogens, including some bacteria, viruses, and parasites, may also take a more direct approach, breaching the blood-brain barrier or directly attacking peripheral nerves. The spirochetal bacterium Borrelia burgdorferi, the causative agent of Lyme disease, demonstrates how one infectious agent can cause a variety of different neurologic syndromes. What starts as a tick bite can lead to Lyme neuropathy, causing nerve damage and excruciating pain, often overlooked among the broader symptoms of the disease. Neuroborreliosis, a manifestation of disseminated Lyme infection, encompasses a spectrum of neurological complications, including peripheral neuropathy, radiculopathy, and meningitis, underscoring the propensity of infectious agents to incite diverse neurological sequelae.
Moreover, infectious pathogens possess a remarkable capacity to infiltrate the nervous system, either through direct invasion or by triggering inflammatory responses that culminate in neurological dysfunction. The neurotropism of certain agents, such as the neurotropic strains of the herpes simplex virus (HSV), exemplifies their ability to target neuronal tissues, leading to conditions like herpes simplex encephalitis. Amidst the backdrop of commonplace infections, the potential for neurological involvement often eludes detection. Consider respiratory viral infections, such as enterovirus, implicated in acute flaccid myelitis (AFM), a poliomyelitis-like syndrome characterized by sudden-onset limb weakness. This juxtaposition emphasizes the inconspicuous yet impactful nature of infectious neuropathies in everyday life.
Among the viral pathogens able to pose significant risks to neurological health, Human Immunodeficiency Virus (HIV) stands as a notable example. HIV, the virus responsible for AIDS, not only compromises the host’s immune system but can also directly invade the CNS, leading to a wide range of neurological complications known as HIV-associated neurocognitive disorders (HAND). These disorders involve cognitive impairment, fortunately mostly mild deficits, but nonetheless capable of significantly impacting the quality of life for affected individuals. HIV can also induce peripheral neuropathies, resulting in symptoms such as tingling, numbness, and weakness in the extremities with distal symmetric polyneuropathy being most commonly observed. The neurotropic nature of HIV indicates its capacity to infiltrate the nervous system, highlighting the critical need for early detection and management to mitigate the neurological burden imposed by this viral adversary.
In the midst of the sobering reality of infectious neuropathies, there are also exciting discoveries. Researchers are uncovering the role of the microbiome in modulating neurological health. Beyond elucidating the neuropathogenesis of already established infections, ongoing research endeavors illuminate novel paradigms underlying the microbiota-gut-brain axis in neurological health and disease. Insights into the bidirectional communication between the gut microbiome and the central nervous system offer promising avenues for therapeutic interventions. This burgeoning field not only enhances our understanding of the interplay between microbes and the nervous system but also holds the potential to revolutionize treatment strategies. Additionally, innovative approaches to combat antibiotic resistance, such as phage therapy and antimicrobial peptides, are gaining traction. Furthermore, the application of artificial intelligence and machine learning techniques may transform infectious disease research and public health surveillance more broadly, allowing for earlier detection of outbreaks and more accurate disease forecasting, that may ultimately also reduce neurologic complications. Infectious neuropathies serve as a reminder of the interconnectedness of our body systems challenging conventional paradigms of disease classification.