Rabies is an infectious zoonosis of viral etiology, characterized by predominant severe damage to the central nervous system, threatening death. A person becomes infected with rabies when bitten by animals. Spreading along the nerve fibers, the rabies virus initially increases their excitability, and then causes the development of paralysis. Penetrating into the tissues of the spinal cord and brain, the virus causes gross violations in the work of the central nervous system, clinically manifested by various phobias, attacks of aggressive arousal, hallucinatory syndrome. Rabies is still an incurable disease. For this reason, it is difficult to overestimate the importance of preventive anti-rabies vaccination carried out to the patient in case of an animal bite.
Rabies is an infectious zoonosis of viral etiology, characterized by predominant severe damage to the central nervous system, threatening death. A person becomes infected with rabies when bitten by animals.
Characteristics of the pathogen
Rabies is caused by a bullet-shaped RNA-containing rhabdovirus with two specific antigens: soluble AgS and surface AgV&. In the process of replication, the virus promotes the appearance of specific inclusions in neurons – eosinophilic bodies of Babesha-Negri. The rabies virus is quite resistant to cooling and freezing, but it is easily inactivated by boiling, exposure to ultraviolet radiation, as well as disinfection with various chemical reagents (lysol, chloramine, carboxylic acid, sulema, etc.).
The reservoir and source of rabies are carnivorous animals (dogs, wolves, cats, some rodents, horses and cattle). Animals secrete the virus with saliva, the contagious period begins 8-10 days before the development of clinical signs. Sick people are not a significant source of infection. Rabies is transmitted parenterally, usually during a human bite by a sick animal (saliva containing the pathogen enters the wound and the virus penetrates into the vascular bed). Currently, there is evidence of the possibility of implementing aerogenic, alimentary and transplacental pathways of infection.
People have a limited natural susceptibility to rabies, the probability of infection in case of infection depends on the location of the bite and the depth of damage and ranges from 23% of cases with limb bites (proximal sections) to 90% in case of a bite to the face and neck. In a third of cases, infection occurs when bitten by wild animals, in other cases, domestic animals and livestock are the culprits of human rabies. In case of timely seeking medical help and carrying out preventive measures, rabies does not develop in infected persons to a full extent.
The rabies virus enters the body through damaged skin and spreads along the fibers of nerve cells, to which it has a pronounced tropicity. In addition, it is possible to spread the virus through the body with the flow of blood and lymph. The main role in the pathogenesis of the disease is played by the ability of the virus to bind acetylcholine receptors of nerve cells and increase reflex excitability, and subsequently cause paralysis. The penetration of the virus into the cells of the brain and spinal cord leads to gross organic and functional disorders of the central nervous system. Patients develop hemorrhages and swelling of the brain, necrosis and degeneration of its tissue.
The pathological process involves cells of the cerebral cortex, cerebellum, optic tubercle and subcutaneous region, as well as the nuclei of cranial nerves. Eosinophilic formations (Babesh-Negri corpuscles) are observed inside the neurons of the brain under microscopy. Pathological cell degeneration leads to functional disorders of organs and systems due to impaired innervation. From the central nervous system, the virus spreads to other organs and tissues (lungs, kidneys, liver and endocrine glands, etc.). Its entry into the salivary glands leads to the release of the pathogen with saliva.
The incubation period of rabies can range from a couple of weeks when the bite is localized on the face or neck to several months (1-3) when the pathogen is introduced in the extremities. In rare cases, the incubation period lasted up to a year.
Rabies occurs with a sequential change of three periods. In the initial period (depression), there is a gradual change in the patient’s behavior. In rare cases, depression is preceded by general malaise, subfebrility, pain in the area of the infection gate (as a rule, a wound that has already healed by the beginning of the disease). Sometimes (extremely rarely) the site of the introduction of the pathogen becomes inflamed again. Usually in this period, the clinic is limited to manifestations from the central nervous system (headaches, sleep disorders, loss of appetite) and the psyche (apathy, depression, irritability, depression and fear attacks). Sometimes patients may feel discomfort in the chest (tightness), suffer from digestive disorders (usually constipation).
The height of the disease (the stage of arousal) occurs 2-3 days after the appearance of the first signs of depression, characterized by the development of various phobias: fear of water, air, sounds and light. Hydrophobia – fear of water – prevents patients from drinking. Characteristic behavior – when holding out a glass of water, the patient gladly takes it, but an attempt to drink the liquid causes an attack of paralyzing fear, suspension of breathing and the patient throws the glass. However, rabies is not always accompanied by hydrophobia, which can make diagnosis difficult. With the progression of the disease, patients suffer from severe thirst, but due to the formed reflex, even the sight and noise of water cause spasms of the respiratory muscles.
Aerophobia is characterized by attacks of suffocation due to air movement, with acustophobia and photophobia, such a reaction is observed to noise and bright light. Attacks of suffocation are short-lived (several seconds), they are accompanied by spasms and convulsions of facial muscles, pupils are dilated, patients are excited, panic-stricken, scream, throw their head back. There is a trembling of the hands. Breathing during paroxysms is intermittent, whistling, breaths are noisy. The muscles of the shoulder girdle are involved in breathing. During this period, patients are in an aggressive excited state, they scream a lot, are prone to haphazard aggressive activity (rushing, can hit or bite). Hypersalivation is characteristic.
With the progression of the disease, arousal attacks are becoming more frequent. There is weight loss, excessive sweating, hallucinations (auditory, visual and olfactory) occur. The duration of the arousal period is 2-3 days, less often it is extended to 6 days.
The terminal stage of the disease is paralytic. During that period, patients become apathetic, their movements are limited, sensitivity is reduced. Due to the subsiding of phobic paroxysms, there is a false impression that the patient has become better, but at this time the body temperature rises rapidly, tachycardia and arterial hypotension develop, paralysis of the extremities, and later cranial nerves. The defeat of the respiratory and vasomotor centers causes cardiac arrest and respiration and death. The paralytic period can last from one to three days.
There are ways to isolate the rabies virus from the cerebrospinal fluid and saliva, in addition, it is possible to diagnose using the reaction of fluorescent antibodies on biopsies of the dermis, corneal prints. But due to the complexity and economic inexpediency, these techniques are not used in wide clinical practice.
Basically, the diagnosis is carried out on the basis of the clinical picture and epidemiological history data. Diagnostic methods that have a lifetime character also include a bioassay on laboratory animals (newborn mice). When infected with a virus isolated from saliva, cerebrospinal fluid or lacrimal fluid, mice die after 6-7 days. Histological analysis of the brain tissue of the deceased patient makes it possible to definitively confirm the diagnosis in case of detection of Babesh-Negri cells in the cells.
Treatment of rabies
Currently, rabies is an incurable disease, therapeutic measures are palliative in nature and are aimed at alleviating the patient’s condition. Patients are hospitalized in a darkened, noise-insulated ward, they are prescribed symptomatic remedies: hypnotics and anticonvulsants, painkillers, tranquilizers. Nutrition and rehydration measures are carried out parenterally.
Currently, new treatment regimens are being actively tested with the help of specific immunoglobulins, immunomodulators, hypothermia of the brain and intensive care techniques. However, rabies is still a fatal disease: death occurs in 100% of cases of clinical symptoms.
Rabies prevention is primarily aimed at reducing the incidence among animals and limiting the likelihood of being bitten by stray and wild human animals. Pets are necessarily subject to routine vaccination against rabies, decreed categories of citizens (veterinary service workers, dog catchers, hunters, etc.) are immunized with an anti-rabies vaccine (triple intramuscular injection). A year later, a revaccination is performed and in the future, if the risk of infection remains high, it is recommended to repeat immunization every three years.
In case of an animal bite, a set of measures aimed at preventing rabies is necessarily carried out: the wound is washed with medical alcohol, treated with antiseptics, an aseptic bandage is applied, after which you should immediately contact a trauma center (or a surgeon or a paramedic of the FAP). A course of preventive anti-rabies vaccination (dry inactivated vaccine) and passive immunization (anti-rabies immunoglobulin) is carried out as soon as possible. The scheme of preventive injections depends on the location of the bite, the depth of the wound and the degree of saliva contamination.