Viral infections of the nervous system

CNS viral infections usually occur within generalized viruses. Multiple nerve structures are often damaged at the same time.
 * gateway of viral infection: respiratory tract, gastrointestinal tract, urogenital tract, skin
 * the infection spreads to the CNS along the peripheral nerves / hematogenously
 * involvement: meninges → meningitis, brain and spinal cord tissues → encephalitis or myelitis, anterior horns → poliomyelitis, sensitive spinal ganglia of spinal cord → radiculitis
 * acute to chronic infections, the virus can survive in nervous structures for years asymptomatically, a number of virosis seasonal occurrence
 * immunosuppression and cytostatics create the conditions for virus replication
 * active immunization (today eg rare polioviruses)
 * diagnosis: detection of virus from cerebrospinal fluid, faeces, nasopharynx, increase in antibody titer in fluid or blood
 * treatment of most viruses only symptomatic, exception: herpes viruses - aciclovir
 * antiviral sera are available for some diseases, active immunizations are given for others

Viral encephalitis
They occur most in the tropics. Viruses affect the brain in 4 ways:
 * 1) directly (acute encephalitis or meningoencephalitis)
 * 2) after various latencies ("slow" viral encephalitis)
 * 3) indirectly via the immune system (allergic, post-infectious or post-vaccination encephalomyelitis)
 * 4) encephalopathy (Reye's syndrome) also develops within the viral infection

Rabies (rabies, lyssa)
Rabies (lyssa) is a viral infectious disease that spreads from wild and domestic animals. Once clinical symptoms break out, the disease is always fatal.

The Czech Republic has been considered "Rabies-free" since 2004 (rabies does not occur in the Czech Republic). In the Czech Republic, you can find imported rabies or rabies after a bat bite. There is an increased risk of rabies at the borders with Poland and Slovakia (these countries are not "Rabies-free").

Pathogenesis

 * Primary encephalitis caused by lyssavirus belonging to the Rhabdoviridae group,
 * transmitted with the saliva of the animal when bitten or infected by scratches,
 * the virus spreads perineurally from the site of contamination to the CNS,
 * the length of the incubation is determined by the distance of the injury from the head (2 weeks to several months).

Pathological-anatomical image

 * In the cytoplasm of infected cells, inclusion Negri bodies,
 * The virus attacks the cerebral cortex, oblongatum, nuclei of the cranial nerves and spinal ganglia.

Clinical signs

 * After incubation, non-specific symptoms appear - increased fatigue, emotional lability, sleep disorders, scar tension,
 * later paroxysms convulsions - pharyngospasm with dysphagia, hydrophobia,
 * profuse salivation and sweating,
 * death in a few days due to symptoms of hyperpyrexia and heart failure.

Differential diagnostics
It is necessary to differentiate tetanus differentially.

Treatment
There is no cure for rabies.

Prophylaxis
It is necessary to have the animal examined by a veterinarian. When bitten by an infected animal or an animal at risk of rabies, so-called post-exposure prophylaxis is necessary. It is a combination of active (vaccine) and passive (antirabies heterologous horse serum) immunization. The vaccine is given in 5 doses on a schedule of 0-3-7-14-28. Pre-exposure prophylaxis is also possible for travelers and veterinarians.

Acquired Immune Deficiency Syndrome (AIDS)
The disease, known since 1981 is caused by the HIV retrovirus. Neuro- and lymphotropic properties allow the virus to invade the CNS, as well as progressively destroy the immune system (destroying T4 lymphocytes). It is transmitted horizontally (sexual intercourse, blood derivatives, parenteral drug use) or vertically (mother-to-child). Groups that are more at risk of infection are, for example, homosexuals, drug addicts, hemophiliacs or children of infected mothers.

Clinical signs
Acute infection is indicated by fever and numbness of the nodes. Anti-HIV antibodies do not appear until 1-3 months at the earliest, and their positivity is the only manifestation in up to 70% of those infected. This stage of symptomatic chronic infection can last for months to years. Patients often have symptoms we call the AIDS-related complex (ARC), which includes diarrhea, lethargy, weight loss, opportunistic infections (candidiasis, impetigo). HIV positivity is also accompanied by lymphopenia, thrombocytopenia. AIDS means progression to severe opportunistic infections and tumors, such as: Neurological manifestations occur in 80% of patients, their onset is related to seroconversion and late AIDS.
 * pneumocystis pneumonia (50%),
 * Kaposi's sarcoma (20%), CNS lymphoma,
 * non-Hodgkin's lymphomas,
 * tuberculosis.

Treatment
Treatment should be started immediately, if cerebral toxoplasmosis is suspected, we administer pyrimethamine or sulfadiazine. If the CT image does not improve, we indicate a biopsy (lymphoma). AIDS inevitably ends in a fatal infection or malignancy. Drugs that mobilize the immune system and affect the replication of the virus, such as zidovudine (AZT), which blocks the production of HIV-specific DNA and thus reduces the replication of the virus, are also being tested. We also use immunomodulators in therapy, such as IFN, IL-2.

Related articles

 * Infectious brain disease
 * Meningeal syndrome
 * Brain abscess