Today, we're going to be talking about enteroviruses, a group of viruses that are responsible for a wide range of diseases including polio, hand foot and mouth disease, and even the common cold. Enteroviruses can also cause infections of the central nervous system as they did in this 28 year old teacher named Todd. Todd had been teaching at the university preschool where he was also doing research for his master's degree in education. One early evening in August, Todd was brought to the By the mother of one of the children in his class who also happened to be a physician. She had come to the school to pick up her son when one of the other teachers told her that Todd was lying down in the library feeling terrible. She went to speak with Todd and took note of a concerning collection of symptoms. She also saw that he looked distinctly unwell, so she decided to bring him to the. At the Todd tells the physician on duty that he's been well until the day before when he noticed that he had a bit of a sore throat. He explains that a lot of the kids at the preschool are sick with summer colds, and he thought he had just caught a cold from one of them. But today, just after lunch, he began to feel feverish, developed a terrible headache, and began vomiting. The Physician asks Todd if he's traveled anywhere recently, or if he's noticed any unusual mosquito or tick bites. But Todd says he's been teaching through the summer and hasn't had any unusual bites or exposures. He's also not currently taking any medications. During his physical exam, the attending physician notices that Todd has a low great fever and a stiff neck. He also experiences a lot of pain extending his leg from a position where his thigh is bent at the hip and knee at 90 degrees. The attending notes that Kernig's sign is positive and also notes that when Todd is asked to lift his head off the table he involuntary lifts his legs as well. Todd's neurological exam is normal. He's lucid and knows where he is and the correct date and time. This collection of signs and symptoms, nuchal rigidity, headache, fever and emesis, leads the attending to have a high index of suspicion that Todd is suffering from meningitis. Meningitis is an acute inflammation of the membranes that cover the brain and spinal cord. These membranes are collectively known as the meninges, and they can become inflamed by infection with viruses, bacteria and other microorganisms, and less commonly by some drugs. The Physician performs a lumbar puncture to obtain a sample of cerebrospinal fluid that can then be used for analysis. The LP sample is sent on for a cell count, gram stain, and analyses of glucose and protein levels, and one tube of CSF is saved for future molecular diagnostics. The CSF gram stain is negative for bacteria. Glucose levels are normal and there's a modest increase in CSF protein concentration. Lymphocytes in the CSF are elevated. This is consistent with a diagnosis of aseptic meningitis, but the exact cause of the inflammation is still unknown. Elevated CSF lymphocytes can be caused by a variety of conditions including viral meningitis, tuberculous meningitis, a subarachnoid hemorrhage and some autoimmune conditions. Because of Todd's exposure to sick children, his symptoms of an upper respiratory tract infection, and the time of year, the Physician feels that viral meningitis is highest on the differential. He sends the tube of CSF saved earlier for molecular diagnostics, including PCR for enterovirus and herpes simplex virus, which are common causes of viral meningitis. Unlike bacterial cultures, a specific virus needs to be suspected when a physician is selecting the right test to confirm the diagnosis. The results of Todd's diagnostics show that his symptoms are caused by an enterovirus and he's diagnosed with enteroviral meningitis. Enteroviruses are sometimes transmitted when people inhale or ingest material that contains infectious viral particles. Sources of infection include being around others who are ill or swimming in contaminated water, like the water found in fresh water lakes, ponds or swimming pools that haven't been adequately chlorinated. This could explain the seasonal increase in enteroviral infections during the summer. Todd likely inhaled or inoculated his oral pharynx with infectious respiratory droplets containing enterovirus particles while he was teaching at the preschool. The virus was then able to enter Todd's body, and colonize the respiratory epithelium, despite the efforts of the respiratory cilia to protect him from viral invasion. Todd's body detected the infection, and deployed inflammatory cells and chemical mediators that lead to his sore throat and fever. Despite these efforts, the virus was able to persist and replicate, giving rise to the primary viremia which in turn allowed the virus to spread via the bloodstream to lymphoid tissues throughout the body. Replication at these new lymphoid sites produced the secondary viremia which is when Todd began to show symptoms of enteroviral meningitis. The viral particles went on to invade the CNS by being carried across the blood brain barrier in infected leukocytes or by infecting cranial or peripheral nerves. Because this virus has evolved to be able to invade the tissues of the nervous system, it's considered neurotropic. The treatment of patients with suspected viral meningitis depends on which virus is causing the infection and how ill the patient appears. Sometimes, specific antivirals are started while the molecular tests are still pending. Some patients, particularly those who are at the extremes of age, either very young or elderly, or those who are immunocompromised, these patients may be considered for empiric antibacterial therapy for 48 hours even if viral meningitis, not bacterial meningitis is the suspected diagnosis. There are a few reasons why. Firstly, these patients are at higher risk for developing bacterial meningitis. Secondly they may not mount a vigorous or typical immune response. And finally, they may not show early signs of deterioration before becoming very ill. Another option is for the physician to simply closely observe the patient without antibiotic therapy. But, if there's any diagnostic uncertainty, then the benefits of empiric antibiotics greatly outweigh the risks. Todd's initial testing was very typical of viral meningitis and the PCR confirmed the diagnosis of enteroviral meningitis. So his doctor prescribed supportive treatment and he received pain control medication, anti-emetics and IV fluids. He was discharged from the hospital the following day and spent a week recovering at home before he was able to return to work.
