Infectious Diseases Of The Ne... Health Article

Rabies

The virus of rabies is introduced into the body through the bite of an infected dog, fox, vole, bat, or other wild animal. It travels centrally along peripheral nerves, producing a focal encephalitis that mainly involves the cervical cord, the brainstem, and the temporal lobes. The latent period between the bite and the clinical features of the disease may be as long as a year.

Clinically, early irritability and agitated delirium progress to muscle hypertonia, especially affecting the pharyngeal muscles, which go into spasm—hence the term hydrophobia. Convulsions and death usually occur within 10 days of the onset.

Human diploid rabies virus vaccine has been found to be strongly immunogenic, and its introduction is an important breakthrough in the prevention of rabies. Rabies immune globulin should be given as soon as possible after a bite. Usually, 50% of the dose is infiltrated at the bite site and the remainder is given intramuscularly.

Acquired Immunodeficiency Syndrome

Infection with the human immunodeficiency virus (HIV) ultimately results in profound deficits in function of the immune system, predisposing the infected individual to severe opportunistic infections and to certain malignancies. In addition to the neurologic involvement caused by HIV itself, these patients are also susceptible to a variety of CNS infections. Ten percent of patients with AIDS present with neurologic problems, but these ultimately occur in at least 75% of cases.

Syndromes of encephalopathy, aseptic meningitis with cranial neuropathy, myelopathy, or multiple mononeuropathy may occur at the time of initial infection with the virus; recovery occurs within a week or so in most cases.

Toxoplasma encephalitis is the most common cause of mass lesions in the brains of patients with AIDS. Headache, confusion, lethargy, focal deficits, seizures, fever, and coma result; chorea, dystonias, myoclonus, and tremor are less common. Mass lesions in patients with AIDS are due either to such opportunistic infections or to tumors. A CT scan typically shows ring-enhancing lesions when toxoplasma, tubercular, candida, or CMV infection is present and with primary CNS lymphoma.

AIDS dementia is a manifestation of the subacute encephalitis that occurs in one third of HIV-infected patients, and it is accompanied by a host of neurologic signs. Apart from the major cognitive symptoms, such as forgetfulness, impaired concentration, confusion, and slowing of thought processes, signs such as apathy, organic psychoses, headache, depression, seizures, myoclonus, cerebellar and pyramidal deficits, neuropathy, and retinopathy are common.

Vacuolar myelopathy leads to paraparesis with spastic weakness, ataxia, and paresthesias in the legs. It is considered to represent the effect of direct HIV infection of the spinal cord.

Cryptococcal and tuberculous meningitis, CMV retinitis, toxoplasma chorioretinitis, herpes simplex myelitis, and spirochetal or viral encephalomyelitis are other frequent complications, as are progressive multifocal leukoencephalopathy, CNS lymphomas, and a painful symmetrical sensorimotor peripheral neuropathy. Again these entities are probably related to direct infection with the HIV virus.

AIDS remains a fatal disease, but prompt diagnosis and treatment of the opportunistic infections have prolonged survival. Toxoplasmosis is treated with pyrimethamine, 200 mg as a loading dose, then 50 to 75 mg daily, with sulfadiazine, 4 gm/day, or clindamycin. All patients who are treated with pyrimethamine or sulfadiazine should also receive folinic acid, 10 mg orally each day.