Nervous System Infections

Highlight Disease ~ Zika Virus Disease

Microcephaly

babies born with abnormally small heads and neurological issues, often due to infections during pregnancy such as Zika virus

Causative agent of microcephaly:

Zika virus in the Flaviviridae family

• related to dengue fever, West Nile fever, and yellow fever

Zika Virus Disease — signs and symptoms:

• Adults: range from none to skin rash, conjunctivitis, and muscle and joint pain

  • also triggers Guillain-Barre syndrome in some adults

• Babies who acquire it during gestation: congenital Zika virus syndrome:

  • small head, vision problems, involuntary movements, seizures, and irritability

  • symptoms of brain stem dysfunction such as swallowing problems are also common

Zika Virus Disease: transmission and epidemiology:

• transmitted by the bite of the Aedes mosquito, via sexual intercourse with infected individuals, and vertically in utero

• 80% of infections are asymptomatic

• between 5 and 10% of Zika-positive mothers have babies affected by the virus

Zika Virus Disease — prevention and treatment:

• no vaccine currently available

• provide supportive measures

• patients experiencing Guillain-Barre syndrome should receive intensive physical therapy and may require mechanical ventilation

Poliomyelitis

• acute enteroviral infection of the spinal cord that can cause neuromuscular paralysis; also known as infantile paralysis

• WHO campaign has greatly reduced the incidence of polio, but no region/culture has escaped its devastation

  • campaign’s goal was to eradicate all remaining wild polioviruses by 2000, and then by 2005

  • the 20th century saw a very large rise in paralytic polio cases due to travel, but a vaccine is available

  • infection was eliminated from the Western Hemisphere in the late 20th century

  • but difficult to eradicate from the developing world

Poliomyelitis — causative agent:

• Poliovirus in the family Picornaviridae, genus Enterovirus:

  • named for its small size (pico)

  • non-enveloped, non-segmented RNA virus

  • naked capsid confers chemical stability and resistance to acid, bile, and detergents

  • survives the gastric environment and other harsh conditions

  • virus is spread through food, water, hands, objects contaminated with feces, and mechanical vectors

Poliomyelitis — pathogenesis and virulence factors:

• after ingestion, polioviruses adsorb to receptors of mucosal cells in the oropharynx and intestine

  • they multiply in mucosal epithelia and lymphoid tissue; large numbers of viruses are shed in the throat, in feces, and some leak into the blood

  • depending on the number of viruses in the blood and the duration of their stay, individuals may develop:

    • no symptoms

    • mild, nonspecific symptoms such as fever and short-term muscle pain

    • devastating paralysis

Poliomyelitis — signs and syndromes:

• short-term, mild viremias

• mild, nonspecific symptoms of fever, headache, nausea, sore throat, and myalgia

• if viremia persists:

  • viruses carried to the CNS through the blood supply

  • spreads along specific pathways in the spinal cord and brain

  • Neurotropic: infiltrates motor neurons of the anterior horn of the spinal cord

  • can also attack spinal ganglia, cranial nerves, and motor nuclei

Poliomyelitis — paralytic disease

• invasion of motor neurons causes flaccid paralysis

• paralysis of the muscles of the legs, abdomen, back, intercostals, diaphragm, pectoral girdle, and bladder can result

Bulbar poliomyelitis:

• brain stem, medulla, or cranial nerves are affected

• loss of control of cardiorespiratory regulatory centers; requires use of mechanical respirators

• unused muscles begin to atrophy, growth is slowed, and severe deformities of the trunk and limbs develop

• crippled limbs are often very painful

Poliomyelitis — treatment:

• alleviation of pain and suffering

• acute phase: muscle spasm, headache, and associated discomfort alleviated by pain-relieving drugs

• respiratory failure may require artificial ventilation maintenance

• prompt physical therapy to diminish crippling deformities and retrain muscles is recommended after the acute phase subsides

Poliomyelitis — prevention:

• vaccination as early in life as possible, usually in 4 doses, starting at 2 months of age

• adult candidates for immunization are travelers and members of the armed forces

What are the 2 forms of the Poliomyelitis vaccine?

1.) Inactivated poliovirus vaccine (IPV) developed by Jonas Salk in 1954

2.) Oral poliovirus vaccine (OPV) developed by Sabin in the 1960s

• contains an attenuated virus that can (rarely) revert to a virulent strain that can cause disease

Meningoencephalitis is caused by which 2 amoebas?

1.) Naegleria fowleri

2.) Acanthamoeba

→ Accidental parasites that invade the body only under unusual circumstances

Naegleria fowleri

reported in people who have been swimming in warm, natural bodies of fresh water

Naegleria fowleri — pathogenesis and virulence factors:

• amoeba are forced into human nasal passages as a result of swimming, diving, or other aquatic activities

• burrows into the nasal mucosa, multiplies, and migrates to the brain and surrounding structures

• PAM

PAM: Primary amoebic meningoencephalitis (part of Naegleria fowleri):

• causes massive destruction of brain and spinal tissue that results in hemorrhage and coma

• death occurs within a week

N. fowleri — transmission and epidemiology:

• wide distribution in fresh bodies of water

• very common: children carry the amoeba as harmless biota, especially during the summer months

• series of events leading to infection is very rare

N. fowleri — prevention and treatment:

• Naegleria meningoencephalitis advances so rapidly that treatment is usually futile:

• early therapy with amphotericin B, sulfadiazine, or tetracycline in some combination can be of some benefit

• because of the wide distribution of the amoeba and its hardiness, no general method of control exists

• public swimming pools and baths must be adequately chlorinated and checked periodically for the amoeba

Acanthamoeba — pathogenesis and virulence factors:

• causes meningoencephalitis similar to Naegleria

• course of infection is lengthier

• disease is called granulomatous amoebic meningoencephalitis (GAM)

Acanthamoeba — transmission and epidemiology:

• invades broken skin, the conjunctiva, and occasionally lungs and urogenital epithelia

• people with traumatic eye injuries, contact lens wearers, and AIDS patients exposed to contaminated water are at risk

Encephalitis

inflammation of the brain

• can be present as acute or subacute

• always a serious condition

• tissues of the brain are sensitive to damage by inflammatory processes

Acute encephalitis:

• almost always caused by viruses borne by insects (arboviruses) like West Nile virus

• others like JC virus and viruses in the herpes family are causative agents

• bacteria can cause encephalitis, but symptoms are more pronounced in the meninges than in the brain

Acute encephalitis — signs and symptoms:

• behavior changes or confusion because of increased inflammation

• decreased consciousness and seizures

• symptoms of meningitis

Acute encephalitis — prevention and treatment:

• empiric treatment with acyclovir in the case of herpesvirus encephalitis

• treatment will do no harm in persons infected with other agents

Various Arthropod-Borne Viruses (Arboviruses)

• most arthropod vectors feed on the blood of hosts

• peak incidences of infections are when the arthropods are actively feeding and reproducing, during late spring to early fall

• warm-blooded vertebrates maintain the virus during cold and dry seasons

• humans are dead-end, accidental hosts (equine encephalitis) or a maintenance reservoir (yellow fever)

Arboviruses impact on humans:

• it is believed that millions of people acquire arbovirus infections each year and thousands die

• one common outcome is an acute fever, often accompanied by a rash

T/F Symptoms and management of encephalitis caused by arboviruses are similar. Transmission and epidemiology of individual viruses are different.

True

Arboviral Encephalitis — Pathogenesis and Virulence Factors

• begins with an arthropod bite, release of virus into tissues, and replication in lymphatic tissues

• prolonged viremia establishes the virus in the brain

• inflammation causes swelling and damage to the brain, nerves, and meninges

T/F All arboviruses are transmitted by mosquitoes

True

Arboviral encephalitis — signs and symptoms:

• extremely variable and include coma, convulsions, paralysis, tremor, loss of coordination, memory deficits, changes in speech and personality, and heart disorders

  • in some cases, survivors experience some degree of permanent brain damage

  • young children and the elderly are most sensitive to injury

  • most people who are infected will show no symptoms

Arboviral infections — culture and diagnosis:

• detecting arboviral infections can be difficult:

• patient history of travel to endemic areas or contact with vectors

• serum analysis

• rapid serological and nucleic acid amplification tests are available for some viruses

Arboviral infections — treatments:

• no satisfactory treatment exists for any of the arboviral encephalitides

• support measures to control fever, convulsions, dehydration, shock, and edema

• control safeguards are aimed at arthropod vectors:

• mosquito abatement by eliminating breeding sites and by broadcast-spreading insecticides has been highly effective in restricted urban settings