50 Rhabdoviruses, Filoviruses, and Bornaviruses 496.E1

C H A P T E R

RHABDOVIRUSES, FILOVIRUSES, 50 AND BORNAVIRUSES

A 15-year-old girl picked up a bat and was bitten on her hand. One month later, she developed double vision, nausea, and vomiting. Over the course of 4 days, her neurologic disease developed, and she had a fever of 38.9° C. Rabies was suspected, and rabies virus–specific antibodies were detected in the patient’s serum and cerebrospinal fluid (1 : 32 titer). The patient was put into a drug-induced coma with ventilator support and treated with intravenous ribavirin for 7 days, when cerebrospinal fluid antibody titers rose to 1 : 2048. After 3 months, she was able to walk with assistance, ride a stationary cycle for 8 minutes, feed herself a soft solid diet, solve math puzzles, use sign language, and was regaining the ability to speak. This is the only example of a patient surviving without having received timely postexposure rabies immunization.* 1. How is rabies infection confirmed? 2. What is the usual disease progression following a bite from a rabid animal? 3. When is antirabies antibody detected in a normal rabies disease presentation? 4. What is postexposure rabies immunization, and why does it work? 5. How does ribavirin inhibit the replication of rabies and other viruses? Answers to these questions are available on StudentConsult.com.

• SUMMARIES CLINICALLY SIGNIFICANT ORGANISMS

Rhabdoviruses • Antibody can block disease Diagnosis • Virus spreads along neurons to salivary Trigger Words • RT-PCR, antigen detection in biopsy, glands and brain presence of Negri bodies in infected cells Mad dog, hydrophobia, salivation, bullet- • Antibody produced after virus reaches brain shaped virion, Negri bodies • Incubation period depends on proximity of Treatment, Prevention, and Control bite to CNS and infectious dose Biology, Virulence, and Disease • Immunization with killed vaccine AFTER bite and antirabies immunoglobulin • Medium size, bullet shaped, enveloped, (−) Epidemiology • Prophylaxis if job-related risk RNA genome • Zoonosis • Inactivated vaccine for pets • Encodes RNA-dependent RNA polymerase, • Reservoir in skunks, raccoons, foxes, • Vaccinia virus hybrid vaccine for wild replicates in cytoplasm badgers, bats (aerosols) animals

• Rhabdoviruses Vesiculovirus (vesicular stomatitis viruses [VSVs]), Lyssavi- rus (Greek for “frenzy”) (rabies and rabies-like viruses), an Members of the family Rhabdoviridae (from the Greek word unnamed genus constituting the plant rhabdovirus group, rhabdos, meaning “rod”) include pathogens for a variety and other ungrouped rhabdoviruses of mammals, birds, fsh, of mammals, fsh, birds, and plants. Te family contains and arthropods. Rabies virus is the most signifcant pathogen of the rhab- *Adapted from Centers for Disease Control and Prevention: Recovery doviruses. Until Louis Pasteur developed the killed-rabies of a patient from clinical rabies—Wisconsin, 2004, MMWR Morb vaccine, a bite from a “mad” dog always led to the charac- Mortal Wkly Rep 53:1171–1173, 2004. teristic symptoms of hydrophobia and certain death.

496 CHAPTER 50 RHABDOVIRUSES, FILOVIRUSES, AND BORNAVIRUSES 496.E1

Answers 1. If possible, the biting animal is captured, killed, and analyzed for rabies. In animals, a brain biopsy is analyzed by direct immunofuorescence detection for rabies antigen or samples taken for genetic analysis by RT-PCR. For the patient, antirabies antibody may be present late in the infection (usually too late to be of help), and an ELISA can be used for detection. Cerebrospinal fuid or saliva can be analyzed by RT-PCR for viral genome. 2. Afer a long incubation period, initial symptoms are fever, malaise, headache, pain or paresthesia (itching) at the site of the bite, gastrointestinal symptoms, fatigue, and anorexia. Tis prodrome usually lasts 2 to 10 days, afer which the neurologic symptoms specifc to rabies appear. Hydrophobia (fear of water) triggered by the pain associated with the patient’s attempts to swallow water, focal and generalized seizures, disorientation, and hallucinations are also common during the neurologic phase. Te paralysis may lead to respiratory failure. Te patient becomes comatose afer the neurologic phase, which lasts from 2 to 10 days. Tis phase almost universally leads to death resulting from neurologic and pulmonary complications. 3. Te antibody is detected late in the course of disease, afer the infection has progressed to generate neurologic symptoms. Analysis is only useful to confrm the diagnosis but not helpful to the patient. Knowing that tissue is contaminated with rabies allows prevention of its use for transplants. 4. Afer being bitten by an animal suspected of carrying rabies, the bite site is washed carefully and then instilled with rabies immune globulin. Te patient then receives four immunizations with rabies antigen. 5. Ribavirin is a guanosine analog that promotes hypermu- tation of the viral genome, leading to production of non- infectious viruses. CHAPTER 50 RHABDOVIRUSES, FILOVIRUSES, AND BORNAVIRUSES 497

Te RNA-dependent RNA polymerase associated with Physiology, Structure, and Replication the nucleocapsid transcribes the viral genomic RNA, pro- Rhabdoviruses are simple viruses encoding only fve producing fve individual messenger RNAs (mRNAs). For rabies teins and appearing as bullet-shaped enveloped virions virus, this occurs in the Negri bodies. Tese mRNAs are then with a diameter of 50 to 95 nm and length of 130 to 380 nm translated into the fve viral proteins. Te viral genomic RNA (Figure 50-1; Box 50-1). Spikes composed of a trimer of the is also transcribed into a full-length, positive-sense RNA glycoprotein (G) cover the surface of the virus. Te viral template that is used to generate new genomes. Te G protein attachment protein, G protein, generates neutralizing anti- is synthesized by membrane-bound ribosomes, processed by bodies. Te G protein of the vesicular stomatitis virus is a the Golgi apparatus, and delivered to the cell surface in simple glycoprotein with N-linked glycan. Tis G protein membrane vesicles. Te M protein associates with the G was used as the prototype for studying eukaryotic glycopro- protein–modifed membranes. tein processing. Assembly of the virion occurs in two phases: (1) assembly Within the envelope, the helical nucleocapsid is coiled of the nucleocapsid in the cytoplasm and (2) envelopment symmetrically into a cylindrical structure, giving it the and release at the cell plasma membrane. Te genome associ- appearance of striations (see Figure 50-1). Te nucleocapsid ates with the N protein and then with the polymerase pro- is composed of one molecule of single-stranded, negative- teins L and NS to form the nucleocapsid. Association of the sense ribonucleic acid (RNA) of approximately 12,000 bases nucleocapsid with the M protein at the plasma membrane and the nucleoprotein (N), large (L), and nonstructural (NS) induces coiling into its condensed form and the characteris- proteins. Te L and NS proteins constitute the RNA- tic bullet shape of the virion. Te virus then buds through dependent RNA polymerase. Te N protein is the major the plasma membrane and is released when the entire structural protein of the virus. It protects the RNA from nucleocapsid is enveloped. Cell death and lysis occur afer ribonuclease digestion and maintains the RNA in a confgu- infection. Te time for a single cycle of replication depends ration acceptable for transcription. Te matrix (M) protein upon the cell type and the inoculum size. lies between the envelope and the nucleocapsid. Te replica- tive cycle of VSV is the prototype for the rhabdoviruses and Pathogenesis and Immunity other negative-strand RNA viruses (see Chapter 36, Figure Rabies infection usually results from the bite of a rabid 36-13). Te viral G protein attaches to the host cell and animal (Box 50-2). Rabies infection of the animal causes virions are internalized by endocytosis. Rabies virus binds to secretion of the virus in the animal’s saliva and promotes either the nicotinic acetylcholine receptor (AChR), neural aggressive behavior (“mad” dog), which in turn promotes cell adhesion molecule (NCAM), or other molecules. Te transmission of the virus. Te virus can also be transmitted viral envelope then fuses with the membrane of the endo- through inhalation of aerosolized virus (as may be found in some on acidifcation of the vesicle. Tis uncoats the nucleo- bat caves), in transplanted infected tissue (e.g., cornea), and capsid, releasing it into the cytoplasm, where replication by inoculation through intact mucosal membranes. takes place. Endosomal vesicles may deliver whole rabies Te virus replicates quietly at the site for days to months virions along the axon to neuronal cell bodies, where its (Figure 50-2) before progressing to the central nervous replication takes place. system (CNS). Rabies virus travels by retrograde axoplasmic

Box 50-2 Disease Mechanisms of Rabies Virus

Rabies is usually transmitted in saliva and acquired from the bite of a rabid animal. Rabies virus is not very cytolytic and seems to remain cell associated. Virus replicates in the muscle at the site of the bite, with minimal or no symptoms (incubation phase). The length of the incubation phase is determined by the infectious dose and the proximity of the infection site to the central nervous system (CNS) and brain. After weeks to months, the virus infects the peripheral nerves and travels up the CNS to the brain (prodrome phase). FIGURE 50-1 Rhabdoviridae seen by electron microscopy: rabies Infection of the brain causes classic symptoms, coma, and death (neu- virus (lef) and vesicular stomatitis virus (right). (From Fields BN: rologic phase). Virology, New York, 1985, Raven.) During the neurologic phase, the virus spreads to the glands, skin, and other body parts, including the salivary glands, from where it is transmitted. Box 50-1 Unique Features of Rhabdoviruses Rabies infection does not elicit an antibody response until the late stages of the disease, when the virus has spread from the CNS to other sites. Bullet-shaped, enveloped, negative-sense, single-stranded RNA viruses Administration of antibody can block progression of the virus and disease that encode fve proteins if given early enough. Prototype for replication of negative-strand enveloped viruses The long incubation period allows active immunization as a postexposure Replication in cytoplasm treatment. 498 MEDICAL MICROBIOLOGY

7 Infection of spinal cord, Box 50-3 Epidemiology of Rabies Virus brainstem, cerebellum, and other brain structures Disease/Viral Factors 8 Descending infection via Virus-induced aggressive behavior in animals promotes virus spread. nervous system to eye, salivary glands, skin, Disease has long, asymptomatic incubation period. and other organs Transmission Zoonosis Reservoir: wild animals Vector: wild animals and unvaccinated dogs and cats 6 Rapid ascent in Source of virus spinal cord Major: saliva in bite of rabid animal (including bats) Minor: aerosols in bat caves containing rabid bats Who Is at Risk? Veterinarians and animal handlers 5 Replication in Person bitten by a rabid animal dorsal ganglion Inhabitants of countries with no pet vaccination program Geography/Season 3 Virion enters peripheral Virus found worldwide, except in some island nations nervous system 4 No seasonal incidence Passive ascent via Modes of Control sensory fibers Vaccination program is available for pets. 1 Virus Vaccination is available for at-risk personnel. inoculated Vaccination programs have been implemented to control rabies in forest mammals. 2 Viral replication in muscle

released, and the infection probably remains hidden from the immune response. Cell-mediated immunity appears to play little or no role in protection against rabies virus infection. FIGURE 50-2 Pathogenesis of rabies virus infection. Numbered Antibody can block the spread of virus to the CNS and steps describe the sequence of events. (Modifed from Belshe RB: brain if administered or generated by vaccination during the Textbook of human virology, ed 2, St Louis, 1991, Mosby.) incubation period. Te incubation period is usually long enough to allow generation of a therapeutic protective antibody response afer active immunization with the killed transport to the dorsal root ganglia and the spinal cord. Once rabies vaccine. the virus gains access to the spinal cord, the brain becomes rapidly infected. Te afected areas are the hippocampus, Epidemiology brainstem, ganglionic cells of the pontine nuclei, and Pur- Rabies is the classic zoonotic infection spread from animals kinje cells of the cerebellum. Te virus then disseminates to humans (Box 50-3). It is endemic in a variety of animals from the CNS via aferent neurons to highly innervated sites worldwide, except in Australia. Rabies is maintained and such as the skin of the head and neck, salivary glands, spread in two ways. In urban rabies, dogs are the primary retina, cornea, nasal mucosa, adrenal medulla, renal paren- transmitter, and in sylvatic (forest) rabies, many species of chyma, and pancreatic acinar cells. Afer the virus invades wildlife can serve as transmitters. In the United States, rabies the brain and spinal cord, encephalitis develops and neurons is more prevalent in cats because they are not vaccinated. degenerate. Despite extensive CNS involvement and impair- Virus-containing aerosols, bites, and scratches from infected ment of CNS function, little histopathologic change can be bats also spread the disease. Te principal reservoir for rabies observed in the afected tissue, other than the presence of in most of the world, however, is the dog. In Latin America Negri bodies (see section on Laboratory Diagnosis). and Asia, this feature is a problem because of the existence Rabies is fatal once clinical disease is apparent. Te length of many stray unvaccinated dogs and the absence of rabies- of the incubation period is determined by the (1) concentra- control programs. Although rare, there are cases of rabies tion of the virus in the inoculum, (2) proximity of the wound transmission via corneal and organ transplants. to the brain, (3) severity of the wound, (4) host’s age, and (5) Because of the excellent dog vaccination program in the host’s immune status. United States, sylvatic rabies accounts for most of the cases In contrast to other viral encephalitis syndromes, rabies of animal rabies in this country. Statistics for animal rabies is minimally cytolytic and rarely causes infammatory lesions. are collected by the Centers for Disease Control and Preven- Viral proteins inhibit apoptosis and aspects of interferon tion, which in 1999 recorded more than 8000 documented action. Neutralizing antibodies are not apparent until afer cases of rabies in raccoons, skunks, bats, and farm animals, the clinical disease is well established. Little antigen is in addition to dogs and cats (Figure 50-3). Badgers and foxes CHAPTER 50 RHABDOVIRUSES, FILOVIRUSES, AND BORNAVIRUSES 499 are also major carriers of rabies in Western Europe. In South transmitted by dogs in 96% of cases. In Latin America, cases America, vampire bats transmit rabies to cattle, resulting in of human rabies primarily result from contact with rabid losses of millions of dollars each year. dogs in urban areas. In Indonesia, an outbreak of more than Although underreported, it is estimated that rabies 200 human cases of rabies in 1999 prompted the killing of accounts for 55,000 deaths (mostly children) annually world- more than 40,000 dogs on the islands. Te incidence of wide, with at least 20,000 deaths in India, where the virus is human rabies in the United States is approximately one case per year, due in large part to efective dog vaccination programs and limited human contact with skunks, raccoons, and bats. Since 1990, human cases of rabies in the United Percent States have been caused primarily by bat variants of the virus. Te World Health Organization estimates that 10 million people per year receive treatment afer exposure to animals suspected of being rabid.

80 Clinical Syndromes (Box 50-4) 70 Rabies is virtually always fatal unless treated by vaccination. 60 Afer a long but highly variable incubation period, the pro- 50 Raccoon drome phase of rabies ensues (Table 50-1). Te patient has 40.6 40 Skunk symptoms such as fever, malaise, headache, pain or pares- 29.4 30 thesia (itching) at the site of the bite, gastrointestinal symp- Bat Other wild 20 Fox toms, fatigue, and anorexia. Te prodrome usually lasts 2 to 14 animals 5.4 10 2.1 10 days, afer which the neurologic symptoms specifc to rabies appear. Hydrophobia (fear of water), the most char- Wild animals acteristic symptom of rabies, occurs in 20% to 50% of patients. It is triggered by the pain associated with the 80 patient’s attempts to swallow water. Focal and generalized 70 seizures, disorientation, and hallucinations are also common during the neurologic phase. Paralysis (15% to 60% of 60 patients) may be the only manifestation of rabies and may 50 lead to respiratory failure. 40 Te patient becomes comatose afer the neurologic phase, which lasts from 2 to 10 days. Tis phase almost universally 30 Other 20 domestic Dog Cat 10 Cattle animals Box 50-4 Clinical Summary 1.6 3.9 1.9 1.2 Rabies: A 3-year-old girl was found to have a bat fying in her bedroom. Domestic animals The bat apparently was there all night. There was no evidence of any bite wound or contact, and the bat was caught and released. Three FIGURE 50-3 Distribution of animal rabies in the United States, weeks later, the child developed a change in behavior, becoming irri- 1999. Percentages relate to the total number of cases of animal table and agitated. This state quickly progressed to confusion, uncon- rabies. (Data from Krebs JW, Rupprecht CE, Childs JE: Rabies sur- trollable thrashing about, and inability to handle her secretions. She veillance in the United States during 1999, J Am Vet Med Assoc eventually became comatose and died from respiratory arrest. 217:1799–1811, 2000.)

Table 50-1 Progression of Rabies Disease Disease Phase Symptoms Time (Days) Viral Status Immunologic Status Incubation phase Asymptomatic 60-365 after bite Low titer, virus in muscle — Prodrome phase Fever, nausea, vomiting, loss of appetite, 2-10 Low titer, virus in CNS — headache, lethargy, pain at site of bite and brain Neurologic phase Hydrophobia, pharyngeal spasms, hyperactivity, 2-7 High titer, virus in brain Detectable antibody in anxiety, depression and other sites serum and CNS CNS symptoms: loss of coordination, paralysis, confusion, delirium Coma Coma, hypotension, hypoventilation, secondary 0-14 High titer, virus in brain — infections, cardiac arrest and other sites Death — — — — CNS, Central nervous system. 500 MEDICAL MICROBIOLOGY leads to death resulting from neurologic and pulmonary workers, laboratory workers who handle potentially infected complications. tissue, and people traveling to areas where rabies is endemic. HDCV is administered intramuscularly to these individuals Laboratory Diagnosis and provides 2 years of protection. Te occurrence of neurologic symptoms in a person who has Ultimately the prevention of human rabies hinges on been bitten by an animal generally establishes the diagnosis efective control of rabies in domestic and wild animals. Its of rabies. Unfortunately, evidence of infection, including control in domestic animals depends on removal of stray and symptoms and the detection of antibody, does not occur until unwanted animals and vaccination of all dogs and cats. A it is too late for intervention. Laboratory tests are usually variety of attenuated oral vaccines have also been used suc- performed to confrm the diagnosis and determine whether cessfully to immunize foxes. A live recombinant vaccinia a suspected individual or animal is rabid (postmortem). virus vaccine expressing the rabies virus G protein is in use Antigen detection using direct immunofuorescence or in the United States. Tis vaccine, which is injected into bait genome detection using reverse transcriptase polymerase and parachuted into the forest, successfully immunizes rac- chain reaction (RT-PCR) are relatively quick and sensitive coons, foxes, and other animals. Accidental injection of a assays that are the preferred methods for diagnosing rabies. woman with this vaccinia-rabies hybrid vaccine resulted in Samples of saliva are easy to test, but serum, spinal fuid, skin immunization against both smallpox and rabies viruses (see biopsy material from the nape of the neck, brain biopsy or Bibliography). autopsy material, and impression smears of corneal epithe- lial cells can also be examined. Infected cells will have intracytoplasmic inclusions con- • Filoviruses sisting of aggregates of viral nucleocapsids (Negri bodies) in afected neurons (see Chapter 39, Figure 39-3). Although Te Marburg and Ebola viruses (Figure 50-4) were classifed their fnding is diagnostic of rabies, Negri bodies are seen in as members of the family Rhabdoviridae but are now classi- only 70% to 90% of brain tissue from infected humans. fed as floviruses (Filoviridae). Tey are flamentous, Rabies antibody titers in serum and cerebrospinal fuid enveloped, negative-strand RNA viruses. Tese agents are usually measured by enzyme-linked immunosorbent cause severe or fatal hemorrhagic fevers and are endemic assay (ELISA). Antibody usually is not detectable until late in Africa. Awareness of the Ebola virus increased afer an in the disease, however. outbreak of the disease in Zaire in 1995, in Gabon in 1996, and also afer the release of the movie Outbreak, based on Treatment and Prophylaxis the book by Robin Cook, and the book Te Hot Zone by Clinical rabies is almost always fatal unless treated with post- Richard Preston. In 2014, an epidemic of Ebola killed many rabies immunization. Once the symptoms have appeared, thousands, mostly in the West African countries of Liberia, little other than supportive care can be given. Tere is one Sierra Leone, and Guinea, and isolated cases have spread case of successful cessation of disease progression by post- throughout the world. exposure ribavirin treatment (see introductory case study). Postexposure prophylaxis is the only hope for preventing Structure and Replication overt clinical illness in the afected person. Although human Filoviruses have a single-stranded RNA genome (4.5 × cases of rabies are rare, approximately 20,000 people receive 106 Da) that encodes seven proteins. Te virions form envel- rabies prophylaxis each year in the United States alone. Pro- oped flaments with a diameter of 80 nm but may also phylaxis should be initiated for anyone exposed by bite or by assume other shapes. Tey vary in length from 800 nm to as contamination of an open wound or mucous membrane to long as 1400 nm. Te nucleocapsid is helical and enclosed in the saliva or brain tissue of an animal suspected to be infected an envelope containing one glycoprotein. Te glycoprotein with the virus, unless the animal is tested and shown not to be rabid. Te frst protective measure is local treatment of the wound. Te wound should be washed immediately with soap and water or another substance that inactivates the virus. Antirabies immunoglobulin is injected near the wound. Subsequently, four immunizations with rabies vaccine are administered within 2 weeks, with one initial dose of human rabies immunoglobulin (HRIG) or equine antirabies serum. Passive immunization with HRIG provides antibody until the patient produces antibody in response to the vaccine. Te slow course of rabies disease allows active immunity to be generated in time to aford protection. Te rabies vaccine is a killed-virus vaccine prepared through chemical inactivation of rabies infected–tissue culture human diploid cells (HDCV) or chick embryo cells. Tese vaccines cause fewer negative reactions than the older vaccines (Semple and Fermi), which were prepared in the brains of adult or suckling animals. Serum monitoring and FIGURE 50-4 Electron micrograph of Ebola virus. (Courtesy preexposure vaccination should be performed on animal Centers for Disease Control and Prevention, Atlanta.) CHAPTER 50 RHABDOVIRUSES, FILOVIRUSES, AND BORNAVIRUSES 501

(GP) is cleaved into two components, and a shorter version Clinical Case 50-1 Ebola is secreted. Te Ebola virus binds to Niemann-Pick C1 (NPC1), a cholesterol transfer protein, and T-cell immuno- Emond and associates described the following case of Ebola infection (Br globulin and mucin domain 1 (TIM-1), which is also the Med J 2:541–544, 1977). Within 6 days of a needle-stick accident while hepatitis A virus receptor. Te virus enters the cell and rep- handling animal liver infected with Ebola virus, a scientist complained of licates in the cytoplasm like the rhabdoviruses. abdominal pain and nausea. He was transferred to a high-security infectious disease unit and placed in an isolation room. At admission (day 1), Pathogenesis he was experiencing fatigue, anorexia, nausea, and abdominal pain and Te floviruses replicate efciently, producing large amounts had a fever of 38° C. Interferon was administered twice a day, and it of virus in endothelial cells, monocytes, macrophage, den- appeared to have worked, except that the next morning his fever returned dritic cells, and other cells. Replication in monocytes elicits (39° C). He was given heat-inactivated convalescent serum with no imme- a cytokine storm of proinfammatory cytokines similar to a diate effect. On day 4, he sweated profusely, and his temperature dropped superantigen-induced cytokine storm. Viral cytopathogen- to normal, but he had a new rash on his chest. At midday of day 4, he esis causes extensive tissue necrosis in parenchymal cells of experienced sudden violent shivering, fever of 40° C, nausea, vomiting, the liver, spleen, lymph nodes, and lungs. Infection of endo- and diarrhea. These symptoms continued for 3 days, with spread of the thelial cells interferes with binding, prevents production of rash across his body. On day 6, more convalescent serum and rehydration cell adhesion proteins, and causes cytolysis, leading to vas- treatment were administered. The patient made a slow recovery over the cular injury and leakage. Strains with mutations in the gly- next 10 weeks. Virus (detected by electron microscopy and inoculation of coprotein gene lack the hemorrhagic component of disease. guinea pigs) was present in his blood from the frst day of symptoms. Te widespread hemorrhage that occurs in afected patients (Currently, the analysis would be performed by reverse transcriptase poly- causes edema and hypovolemic shock. Te virus can also merase chain reaction, with less risk to laboratory personnel.) Virus titers evade host innate and immune responses. A small soluble dropped by 1000-fold after interferon treatment and were undetectable glycoprotein is shed and can inhibit neutrophil activation by day 9. Treatment of the patient and handling of samples were performed and block antibody action. Te viral proteins can also inhibit under the strictest isolation conditions available at the time. Even though interferon production and action. the scientist took precautions and soaked his hand in bleach as soon as possible, his fate was already sealed. Luckily, interferon therapy and Epidemiology convalescent serum were available to limit the extent of disease progres- Marburg virus infection was frst detected among laboratory sion. In their absence, he would have died from a rapidly progressing workers in Marburg, Germany, who had been exposed to hemorrhagic disease. tissues from apparently healthy African green monkeys. Rare cases of Marburg virus infection have been seen in Zimba- bwe and Kenya. occur in as many as 90% of patients with clinically evident Ebola virus was named for the river in the Democratic disease. Republic of Congo (formerly Zaire) where it was discovered. Outbreaks of Ebola virus disease have occurred in the Laboratory Diagnosis Democratic Republic of Congo, Sudan, and, most recently, All specimens from patients with a suspected flovirus infec- Liberia, Sierra Leone, and Guinea. During an outbreak, the tion must be handled with extreme care to prevent accidental Ebola virus is so lethal it can eliminate the susceptible popu- infection. Handling of these viruses requires level 4 isola- lation before it can be spread from the region. In urban areas, tion procedures that are not routinely available. Viral anti- spread of the virus is more difcult to control. In rural areas gens can be detected in tissue by direct immunofuorescence of central Africa, as much as 18% of the population has analysis and in fuids by ELISA. RT-PCR amplifcation of the antibody to this virus, indicating that subclinical infections viral genome in secretions can be used to confrm the diag- do occur. nosis and minimize handling of samples. Tese viruses may be endemic in bats or wild monkeys and can be spread to humans and between humans. Contact Treatment, Prevention, and Control with the animal reservoir or direct contact with infected Antibody-containing serum, artifcially produced antibody blood or secretions can spread the disease. Tese viruses (ZMAPP), and interferon and ribavirin therapies have been have been transmitted by accidental injection and through tried in patients with flovirus infections. Infected patients the use of contaminated syringes. Health care workers should be quarantined, and contaminated animals should be tending to the sick and monkey handlers may be at risk. In sacrifced. Handling of the viruses, infected individuals, dead response to the 2014 epidemic, screening similar to that for bodies, and contaminated materials requires very stringent SARS coronavirus was initiated at major airports, and all (level 4) isolation procedures. patients in the United States with fulike symptoms are asked for their travel history. • Borna Disease Virus Clinical Syndromes Marburg and Ebola viruses (Clinical Case 50-1) are the most Borna disease virus (BDV) is the only member of a family severe causes of viral hemorrhagic fevers. Te illness usually of enveloped, negative-strand RNA viruses. BDV was frst begins with fulike symptoms such as headache and myalgia. associated with infection of horses in Germany. Te virus Nausea, vomiting, and diarrhea occur within a few days; a has received considerable recent interest because of its asso- rash also may develop. Subsequently, hemorrhage from mul- ciation with specifc neuropsychiatric diseases such as tiple sites (especially the gastrointestinal tract) and death schizophrenia. 502 MEDICAL MICROBIOLOGY

Centers for Disease Control and Prevention: Rabies vaccine, absorbed: a Structure and Replication new rabies vaccine for use in humans, MMWR Morb Mortal Wkly Rep 37:217–223, 1988. Te 8910-nucleotide-long genome of BDV encodes fve Cohen J, Powderly WG: Infectious diseases, ed 2, St Louis, 2004, Mosby. detectable proteins, including a polymerase (L), nucleopro- Fishbein DB: Rabies, Infect Dis Clin North Am 5:53–71, 1991. tein (N), phosphoprotein (P), matrix protein (M), and enve- Flint SJ, Enquist LW, Racaniello VR, et al: Principles of virology: molecular lope glycoprotein (G). Unlike most negative-strand viruses, biology, pathogenesis and control of animal viruses, ed 3, Washington, DC, 2009, American Society for Microbiology Press. BDV replicates in the nucleus. Although this is similar to Knipe DM, Howley PM: Fields virology, ed 6, Philadelphia, 2013, Lippincott the orthomyxoviruses, BDV difers in that its genome is Williams & Wilkins. unsegmented. Plotkin SA: Rabies: state of the art clinical article, Clin Infect Dis 30:4–12, 2000. Pathogenesis Richman DD, Whitley RJ, Hayden FG: Clinical virology, ed 3, Washington, DC, 2009, American Society for Microbiology Press. BDV is highly neurotropic and capable of spreading through- Rupprecht CE: Human infection due to recombinant vaccinia-rabies glyco- out the CNS. BDV also infects parenchymal cells of diferent protein virus, N Engl J Med 345:582–586, 2001. organs and peripheral blood mononuclear cells. Te virus is Schnell MJ, McGettigan JP, Wirblich C, et al: Te cell biology of rabies not very cytolytic and establishes a persistent infection in the virus: using stealth to reach the brain, Nat Rev Microbiol 8:51–61, 2010. infected individual. T-cell immune responses are important Steele JH: Rabies in the Americas and remarks on the global aspects, Rev for controlling BDV infections but also contribute to tissue Infect Dis 10(Suppl 4):S585–S597, 1988. damage leading to disease. Strauss JM, Strauss EG: Viruses and human disease, ed 2, San Diego, 2007, Academic. Clinical Syndromes Warrell DA, Warrell MJ: Human rabies and its prevention: an overview, Rev Infect Dis 10(Suppl 4):S726–S731, 1988. Although there is limited understanding of the BDV disease Winkler WG, Bogel K: Control of rabies in wildlife, Sci Am 266:86–92, in humans, infection of animals can result in subtle losses of 1992. learning and memory and in fatal immune-mediated menin- Wunner WH, Larson JK, Dietzschold B, et al: Te molecular biology of goencephalitis. Many of the outcomes of BDV infection of rabies viruses, Rev Infect Dis 10(Suppl 4):S771–S784, 1988. laboratory animals resemble human neuropsychiatric dis- Filoviruses eases, including depression, bipolar disorder, schizophrenia, Centers for Disease Control and Prevention: Ebola (Ebola virus disease). and autism. Te presence of antibodies to the virus and/or www.cdc.gov/vhf/ebola/. Accessed October 14, 2014. Groseth A, Feldmann H, Strong JE: Te ecology of Ebola virus, Trends infected peripheral blood mononuclear cells in higher-than- Microbiol 15:408–416, 2007. background numbers of patients with schizophrenia, autism, King JW: Ebola, 2014. http://emedicine.medscape.com/article/216288- and other neuropsychiatric diseases suggests that BDV either overview. Accessed October 14, 2014. causes or exacerbates these mental illnesses. Klenk HD: Marburg and Ebola viruses, Curr Top Microbiol Immunol 235:225, 1999. Epidemiology Mohamadzadeh M, Chen L, Schmaljon AL: How Ebola and Marburg viruses battle the immune system, Nat Rev Immunol 7:556–567, BDV is capable of infecting many diferent mammalian 2007. species (zoonosis), including horses, sheep, and humans. Preston R: Te hot zone, New York, 1994, Random House. Most outbreaks of the virus have occurred in central Europe, Sodhi A: Ebola virus disease, Postgrad Med 99:75–76, 1996. but it has also been detected in North America and Asia. Bornaviruses Neither the reservoir nor the mode of transmission of BDV Jordan I, Lipkin WI: Borna disease virus, Rev Med Virol 11:37–57, is known. Higher levels of infection of humans are present 2001. Richt JA, Pfeufer I, Christ M, et al: Borna disease virus infection in animals where outbreaks in horses have been observed. and humans, Emerg Infect Dis 3:343–352, 1997. www.cdc.gov/ncidod/ Laboratory Diagnosis eid/vol3no3/richt.htm. Websites Infection can be detected by direct analysis for the viral Centers for Disease Control and Prevention: Ebola (Ebola virus disease). genome and mRNA in peripheral blood mononuclear cells www.cdc.gov/vhf/ebola/outbreaks/guinea/. Accessed April 4, 2015. using RT-PCR. Serologic analysis of antibody to the viral Centers for Disease Control and Prevention: Ebola hemorrhagic fever. proteins continues to be used to identify an association of www.cdc.gov/vhf/ebola/index.html. Accessed May 11, 2015. BDV with human diseases. Centers for Disease Control and Prevention: Rabies. www.cdc.gov/rabies/. www.cdc.gov/features/dsRabies/index.html. Accessed April 4, 2015. Gompf SG, Pham TM, Somboonwit C, et al: Rabies. http://emedicine Treatment .medscape.com/article/220967-overview. Accessed April 4, 2015. Similar to many other RNA viruses, BDV is sensitive to riba- Hatalski CG, Lewis AJ, Lipkin WI: Borna disease, Emerg Infect Dis 3:129– virin treatment. Ribavirin treatment may be a reasonable 135, 1997. www.cdc.gov/ncidod/EID/vol3no2/hatalski.htm. Accessed April 4, 2015. treatment approach for some psychoneurologic disorders if Kapitanyan R, Pryor PW II, Bertolini J, et al: Emergency treatment of rabies. BDV is demonstrated as a cofactor. http://emedicine.medscape.com/article/785543-overview. Accessed April 4, 2015. King JW, Markanday A: Ebola virus. http://emedicine.medscape.com/ Bibliography article/216288-overview. Accessed April 4, 2015. Richt JA, et al: Borna disease virus infection in animals and humans, Emerg Anderson LJ, Nicholson TG, Tauxe RV, et al: Human rabies in the United Infect Dis 3:129–135, 1997. wwwnc.cdc.gov/eid/article/3/3/pdfs/97-0311 States, 1960–1979: epidemiology, diagnosis, and prevention, Ann Intern .pdf. Accessed May 11, 2015. Med 100:728–735, 1984. WHO: Rabies. www.who.int/topics/rabies/en/. Accessed April 4, 2015. CHAPTER 50 RHABDOVIRUSES, FILOVIRUSES, AND BORNAVIRUSES 502.E1

Case Study and Questions An 11-year-old boy was brought to a hospital in California afer falling; his bruises were treated, and he was released. Te following day, he refused to drink water with his medi- cine, and he became more anxious. Tat night he began to act up and hallucinate. He also was salivating and had dif- fculty breathing. Two days later, he had a fever of 40.8° C (105.4° F) and experienced two episodes of cardiac arrest. Although rabies was suspected, no remarkable data were obtained from a computed tomographic image of the brain or cerebrospinal fuid analysis. A skin biopsy from the nape of the neck was negative for viral antigen on day 3 but positive for rabies on day 7. Te patient’s condition continued to deteriorate, and he died 11 days later. When the parents were questioned, it was learned that 6 months earlier, the boy had been bitten on the fnger by a dog while on a trip to India. 1. What clinical features of this case suggested rabies? 2. Why does rabies have such a long incubation period? 3. What treatment should have been given immediately afer the dog bite? What treatment should have been given as soon as the diagnosis was suspected? 4. How do the clinical aspects of rabies difer from those of other neurologic viral diseases? Answers 1. Rabies is suggested by the boy’s refusal to drink (hydrophobia), hallucinations, anxiety, salivation, difculty breathing, and fever. 2. Rabies has a long incubation period because it is not very cytolytic, and once it enters the neuron, it is relatively hidden from immune responses. Te characteristic disease signs occur only when the virus has reached the brain and starts to replicate and cause damage. 3. Immediately afer the dog bite, the bite site should have been washed and the child should have been injected with rabies-specifc immune globulin as close to the site as possible. A course of immunization with the inactivated rabies vaccine should have also been initiated as soon as possible. 4. Unlike other neurologic viral diseases, rabies infection is undetectable until it reaches the brain (too late for treatment), and then it infects the salivary gland, causing painful swallowing and potential infection of others.