Rabies is a viral infection that attacks the central nervous system, leading to inflammation in the brain and spinal cord. This disease is nearly 100% fatal once clinical symptoms begin to appear. Hydrophobia, which translates to the fear of water, is a real and characteristic sign of the disease, though it does not occur in every case. The symptom results from the virus’s effect on the body’s neurological controls.
Understanding the Cause of Hydrophobia
The term hydrophobia refers to a severe physical reaction to the attempt to swallow liquids, not a psychological fear of water. The rabies virus targets and inflames the brainstem, the area responsible for controlling involuntary functions like breathing and swallowing. This neurological damage results in extreme hypersensitivity and painful muscle spasms in the throat and larynx.
When a person with advanced rabies attempts to drink water, the effort triggers violent, involuntary contractions of the swallowing muscles. This difficulty swallowing, known as dysphagia, is excruciatingly painful and can lead to a choking sensation. The anticipation of this agony causes the person to actively avoid water, resulting in the clinical sign of hydrophobia.
These painful spasms can also be triggered by other stimuli, such as a slight draft of air on the face, a condition known as aerophobia. The intense pain and muscle rigidity are a consequence of the virus disrupting the neural pathways that govern the protective reflexes of the airway. This inability to swallow also causes saliva to accumulate, leading to the excessive drooling associated with the disease.
The Progression of Rabies Symptoms
The course of rabies infection is typically divided into three distinct phases following exposure. The incubation period is highly variable and can last from a few days to over a year, though it commonly lasts one to three months. During this time, the virus travels from the entry site, such as a bite wound, along the peripheral nerves toward the central nervous system, and the patient experiences no symptoms.
The prodromal phase follows, lasting approximately two to ten days, as the virus enters the central nervous system. Symptoms are non-specific and mimic a mild flu, including fever, headache, and general discomfort. A unique symptom that can appear early is an abnormal sensation, like tingling, pain, or itching, at the site of the original bite or scratch.
The acute neurological phase is the final stage, where the disease manifests in one of two forms. The furious, or encephalitic, form is the most common, accounting for about 80% of human cases. This form is characterized by hyperactivity, agitation, and aggression, and is the presentation where both hydrophobia and aerophobia are observed. These intense episodes of excitement and delirium can fluctuate with periods of relative calm.
The second form is paralytic, or “dumb” rabies, which occurs in the remaining 20% of cases and runs a less dramatic course. Instead of agitation, the patient experiences progressive muscle weakness and paralysis, often starting in the limb closest to the initial infection site. While the furious form leads to death quickly, usually within a week, the paralytic form progresses more slowly.
Rabies Transmission and Post-Exposure Treatment
The rabies virus is a zoonotic disease, transmitted primarily through the saliva of an infected mammal. Transmission typically occurs through a bite or a scratch that breaks the skin. Worldwide, dogs are the most common source of human infection, but in the United States, the disease is more prevalent in wild animals like bats, raccoons, skunks, and foxes.
Once a person is exposed to a potentially rabid animal, wound cleansing is a life-saving measure. The wound should be washed with soap and water for at least fifteen minutes to reduce the number of viral particles. This action can markedly decrease the likelihood of developing the disease.
Following wound care, Post-Exposure Prophylaxis (PEP) must be administered immediately, before symptoms begin. PEP has two components that work together to prevent the infection from reaching the central nervous system. The first component is Rabies Immune Globulin (RIG), which provides immediate, passive immunity by injecting antibodies into and around the wound site.
The second component involves a series of rabies vaccines, which stimulate the patient’s own immune system to produce antibodies for long-term, active protection. This vaccine series is administered over a set schedule, typically four doses given over a fourteen-day period. PEP is effective in preventing rabies if administered promptly and correctly before the onset of the neurological phase.