for 60 days). Delay in initiating antibiotics in patients with pulmonary disease resulted in a
40% to 75% mortality. Cutaneous disease is usually treated for 60 days.
Rabies (119–126)
Virology: Rabies virus is a negative-stranded enveloped lyssavirus (lyssavirus type 1). Classical
rabies virus is the only naturally occurring lyssavirus in the western hemisphere. There are
seven genotypes and seven serotypes. With the exception of the Lagos bat virus, all have
caused human disease. The virus is stable between pH 3 and 11 and will survive for years at
708 C or when freeze-dried and stored at 0 8 Cto4 8 C. Phenol, detergents, and formalin
disinfectants inactivate the virus.
Risk of transmission: Rabies is commonly transmitted by a bite or lick of a rabid animal.
Airborne transmission has been documented in caves and in laboratory incidents. Corneal
transplants have been responsible for a number of human-to-human infections. Rabies virus
may be transmitted from human to human as the virus has been isolated from saliva,
respiratory secretions, sputum, nasal swabs, pharyngeal swabs, eye swabs, tears, cerebrospinal
fluid, urine, blood, and serum. Anecdotal reports of rabies transmission by lactation, kissing, a
bite, intercourse, providing health care, and transplacental (human) have been reported. Bait
laced with attenuated rabies virus has transmitted the infection to animals and the
consumption of dying or dead vampire bats has transmitted the infection to foxes and skunks.
Cryptogenic rabies (no evidence or history of an animal bite) represents the largest group
of human rabies cases in the United States. Two strains of rabies virus associated with two
species of bats rarely found among humans were responsible for the majority of cases. These
two strains of rabies virus (i) replicate at lower temperatures, (ii) easily infect skin because of
their ability to infect fibroblasts and epithelial cells, (iii) grow in higher titers in epithelial and
muscle tissue as compared to dog or coyote street rabies virus, and (iv) have changes in the
antigenic sites that increases infectivity.
Incubation period: The averageincubation period (Stage I)is one to two months (range:
4 days to 19 years). Seventy-five percent of symptoms develop 20 to 90 days after exposure.
Clinical disease: Theprodromal period (Stage II)lasts for 10 days. Patients display anxiety
and/or depression. Half the patients have fever and chills and in some patients, gastrointes-
tinal symptoms predominate including nausea, vomiting, diarrhea, and abdominal pain. At
the bite site or proximally along the nerve radiation, there is itching, pain, or paresthesia.
Myoedema(mounding of a part of the muscle when hit with the reflex hammer) may be
demonstrated. If present, this sign persists throughout the course of disease.
Symptomatic Rabies (Stage III)
Symptomatic rabies (stage III) (2–14 days—average survival 5–7 days) manifests itself as
furious rabies in 80% of cases. Patients are agitated, hyperactive, waxing and waning alertness,
bizarre behavior, hallucinations, aggression, with intermittent lucid periods. There is
piloerection, excessive salivation, sweating, priapism, repeated ejaculations, and neurogenic
pulmonary edema. Hydrophobia begins with difficulty swallowing liquids resulting in
pharyngeal and laryngeal spasms and aspiration. As it becomes more severe, the sight of
water triggers spasms.Aerophobia(spasms triggered by gently fanning the face) is often
present. Seizures occur near death.
Presenting symptoms may mimic schizophrenia or delirium tremors.
Symptomatic dumb or paralytic rabiespatients have a longer average survival (13 days).
Patients present with weakness or paralysis in a single limb or may present with quadriplegia.
There is pain and fasciculation in the affected muscle groups, and sensory abnormalities in
some patients. Some patients have meningeal signs but normal mentation. Cranial nerve
abnormalities develop and patients appear expressionless. Twenty percent of patients develop
Guillain–Barre syndrome. Some patients survive as long as a month without respiratory
support but eventually die with paralysis of respiratory and swallowing muscles.
Coma (Stage IV)
Coma (stage IV) may occur immediately after symptoms appear or up to two weeks later.
480 Cleri et al.