INFECTIOUS DISEASE

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VIROLOGY - CHAPTER  TWENTY TWO

VIRAL DISEASES TRANSMITTED BY RODENTS OR FOR WHICH THE RESERVOIR OR VECTOR IS UNCLEAR

Dr. Margaret Hunt

VIRAL DISEASES TRANSMITTED BY RODENTS

Note: Rodents can be infected by rabies virus although they are rarely, if ever, involved in transmission to humans. Rabies is the subject of a separate chapter.

ARENAVIRUS FAMILY

All of the above arenaviruses (and other arenaviruses causing hemorrhagic fever not listed here) have a rodent vector. The arenavirus-associated hemorrhagic fevers have a high case-fatality rate (5 - 35%). The arenaviruses seem to establish persistent infections easily in certain rodents, which get a viremia and a viruria, and shed virus in urine, stools and saliva. Humans are thought to acquire infection from contact with contaminated materials, contaminated food, or aerosolized droppings, nesting materials, etc. Disease in humans often show the following: dehydration, hemoconcentration, hemorrhage, shock syndrome, cardiovascular collapse. In 1999-2000, there were reports of three deaths apparently due to a North American arenavirus (Whitewater Arroyo).  It is not clear if there are other unrecognized cases of this virus or what the case fatality rate is.  

Lymphochoriomeningitis is acquired from close contact with rodents or rodent contaminated materials or in rodent breeding facilities. Infections are frequently asymptomatic. Clinical infections are not usually fatal, but there may be some long-term complications. It is not associated with hemorrhagic fever, but can cause meningitis, encephalitis, myelitis.

The incubation period of LCMV infection is usually between 8 and 13 days. A characteristic biphasic febrile illness then follows. The initial phase, which may last as long as a week, typically begins with any or all of the following symptoms: fever, malaise, anorexia, muscle aches, headache, nausea, and vomiting. Other symptoms that appear less frequently include sore throat, cough, joint pain, chest pain, testicular pain, and parotid (salivary gland) pain. Following a few days of remission, the second phase of the disease occurs, consisting of symptoms of meningitis (for example, fever, headache, and a stiff neck) or characteristics of encephalitis (for example, drowsiness, confusion, sensory disturbances, and/or motor abnormalities, such as paralysis). LCMV has also been known to cause acute hydrocephalus, which often requires surgical shunting to relieve increased intracranial pressure. In rare instances, infection results in myelitis (inflammation of the spinal cord) and presents with symptoms such as muscle weakness, paralysis, or changes in body sensation.  (CDC)

WEB RESOURCES
Lassa Fever Virus
CDC Information - Lassa Fever 
WHO Fact Sheet - Lassa Fever 
 

CASE REPORTS

Lymphocytic choriomeningitis deaths from an Arenavirus infection

The hantavirus genus differs from other members of Bunyaviridae in that members are transmitted by rodents (rather than arthropods). Each hantavirus is only transmitted by a limited number of genera/species of rodent. Infected rodents can spread virus via saliva, urine (they get a viruria) or droppings. When fresh urine, droppings or recently contaminated nesting material is swept up or disturbed, the virus can be aerosolized and inhaled. Some of these viruses can cause severe disease, but even for these viruses many infections are sub-clinical, or very mild and never diagnosed.

i) Associated with hemorrhagic fever with renal syndrome (HFRS)

Korean hemorrhagic fever has a case-fatality rate of about 7%. Other members of the hantaviruses which cause HFRS (hemorrhagic fever with renal syndrome) tend to have a lower fatality rate. Transmission appears to be via inhalation of, or contact with, rodent urine, droppings or saliva.

ii) Associated with severe pulmonary syndrome

These are a newly recognized (1993) group of hantaviruses in North and South America that is transmitted by rodents (by inhalation or contact with excreta) and causes Hantavirus Pulmonary Syndrome (HPS) rather than hemorrhagic fever. 

These hantavirus pulmonary syndrome viruses have a high case fatality rate of ~36%. The viruses are widely distributed throughout the US but relatively rarely cause human disease - about 380 known cases so far in the US. Initial symptoms often include fever, myalgia, nausea, vomiting and a cough; this may progress to dizziness and shortness of breath as lungs fill with fluid followed by acute respiratory distress. There are a several hantaviruses which have been associated with this syndrome, one of the best known of the United States HPS-associated viruses is Sin Nombre virus.

WEB RESOURCES
Hantavirus Pulmonary Syndrome --- United States: Updated Recommendations for Risk Reduction (2002) 
CDC

  Transmission electron micrograph of a virus that causes Hantavirus pulmonary syndrome (Sin Nombre virus). CDC/Cynthia Goldsmith  csg1@cdc.gov 

  New World Hanatviruses CDC

  Map of the United States and adjacent areas showing distribution of Peromyscus maniculatus and location of hantavirus pulmonary syndrome cases, January 27, 1997. CDC

Radiographic Progression of HPS in the Lungs CDC

Hantavirus Pulmonary Syndrome Clinical Progression CDC

  Hantavirus Pulmonary Syndrome  Common Laboratory Findings  CDC

Histopathology of hanatvirus pulmonary syndrome  Other Organs CDC 

Ebola Virus - CDC

Transmission electron micrograph of Marburg virus. Virions are often seen bent into sixes and hairpin configurations. Filovirus   CDC/Dr. Erskine Palmer 

WEB RESOURCES
Ebola virus

CDC Information - Ebola 
CDC - Outbreaks of Ebola 
WHO Fact Sheet - Ebola 

EBOLA AND MARBURG VIRUSES

Ebola and Marburg viruses cause hemorrhagic fevers and have a case-fatality rate which can be as high as 60-90% for certain strains of the viruses. These viruses occur in Africa, but the natural reservoir is unknown. They occasionally infect humans, but the means by which this occurs is usually not clear. 

Patients have severe hemorrhages and there is a lot of virus present, so stringent barrier nursing techniques are needed to prevent further spread. There have been a few cases where humans have been infected by apparently healthy laboratory monkeys.

Ebola virus, which is named after a river in the Democratic Republic of the Congo, infects humans and other primates and was first identified in 1976. The virus is a negative strand RNA filovirus

Disseminated intravascular coagulation (DIC) leading to tissue ischemia and eventual depletion of clotting factors is a typical feature of filovirus infections. Currently several anti-clotting agents are being tested for their effectiveness at preventing the DIC in animal models.

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