Hemorrhagic Fevers (Lassa Fever - Arenaviruses)
Overview
Plain-Language Overview
Hemorrhagic fevers (Lassa fever - Arenaviruses) are serious viral infections that primarily affect the blood vessels and can cause widespread bleeding. The illness is caused by the Lassa virus, which is transmitted to humans through contact with urine or feces of infected rodents. Symptoms often start with fever, weakness, and muscle pain, and can progress to more severe signs like bleeding from the mouth, nose, or internal organs. The disease mainly impacts the immune system and can lead to life-threatening complications if untreated. It is most common in parts of West Africa where the rodent hosts live close to humans.
Clinical Definition
Hemorrhagic fevers (Lassa fever - Arenaviruses) are acute viral illnesses caused by the Lassa virus, an enveloped RNA virus of the Arenaviridae family. The core pathology involves systemic vascular injury leading to increased capillary permeability and hemorrhage. Transmission occurs primarily through exposure to excreta of infected Mastomys rodents or via person-to-person contact with bodily fluids. The disease manifests with fever, malaise, hemorrhagic signs, and multi-organ involvement, including hepatic and renal dysfunction. It is a significant cause of morbidity and mortality in endemic regions due to its potential for severe hemorrhage and shock. The infection also poses a risk of nosocomial outbreaks in healthcare settings without proper precautions.
Inciting Event
Inhalation or ingestion of aerosolized rodent urine or feces contaminated with Lassa virus initiates infection.
Direct contact with infected bodily fluids during care of patients or handling of contaminated materials triggers transmission.
Nosocomial exposure through breaches in infection control practices can initiate outbreaks.
Latency Period
The incubation period ranges from 6 to 21 days after exposure to the virus.
Symptoms typically develop within 1 to 3 weeks following the inciting event.
Diagnostic Delay
Early symptoms are nonspecific and mimic common febrile illnesses such as malaria or typhoid fever.
Limited access to specific diagnostic tests like RT-PCR in endemic areas delays confirmation.
Low clinical suspicion due to overlapping symptoms with other tropical diseases contributes to missed diagnosis.
Clinical Presentation
Signs & Symptoms
Acute onset of fever, malaise, and headache is typical in early infection.
Progressive pharyngitis with sore throat and painful ulcers in the oropharynx.
Gastrointestinal symptoms including vomiting, diarrhea, and abdominal pain are common.
Hemorrhagic signs such as epistaxis, hematuria, and bleeding from venipuncture sites.
Sensorineural hearing loss occurs in a significant subset during or after infection.
History of Present Illness
Initial presentation includes gradual onset of fever, malaise, headache, and myalgia over several days.
Progression to pharyngitis, retrosternal chest pain, and abdominal pain occurs within the first week.
Development of facial swelling, conjunctivitis, and mucosal bleeding signals worsening disease.
Severe cases show hypotension, shock, and multi-organ dysfunction in the second week.
Past Medical History
History of recent travel or residence in endemic West African regions is relevant.
Prior exposure to rodents or known Lassa fever cases increases suspicion.
No specific chronic conditions alter susceptibility, but immunosuppression may worsen outcomes.
Family History
There are no known hereditary or familial syndromes associated with Lassa fever.
Clusters of cases may occur in families due to shared environmental exposure to infected rodents.
No genetic predisposition has been identified.
Physical Exam Findings
Presence of petechiae and mucosal bleeding indicating hemorrhagic manifestations.
Facial edema and conjunctival injection are common early signs of vascular leakage.
Hypotension and tachycardia may reflect progressive shock in severe cases.
Hepatomegaly and abdominal tenderness can be observed due to liver involvement.
Neurological signs such as confusion or seizures may indicate central nervous system involvement.
Diagnostic Workup
Diagnostic Criteria
Diagnosis is established by detecting Lassa virus RNA using reverse transcriptase-polymerase chain reaction (RT-PCR) or by identifying Lassa virus-specific IgM antibodies via serologic testing. Viral isolation in cell culture can confirm infection but is less commonly used due to biosafety concerns. Clinical suspicion arises in patients with compatible symptoms and epidemiologic exposure in endemic areas. Laboratory findings often include thrombocytopenia, elevated liver enzymes, and proteinuria, supporting the diagnosis but are not definitive without virologic confirmation.
Pathophysiology
Key Mechanisms
Viral replication of Lassa virus in endothelial cells leads to widespread vascular endothelial damage and increased vascular permeability.
Immune dysregulation with impaired type I interferon response contributes to uncontrolled viral spread and systemic inflammation.
Coagulopathy results from consumption of clotting factors and platelet dysfunction, causing hemorrhagic manifestations.
Multiorgan failure occurs due to direct viral cytopathic effects and secondary hypoperfusion from shock.
| Involvement | Details |
|---|---|
| Organs | Liver is a major site of viral replication and injury, leading to elevated transaminases and coagulopathy. |
Kidneys may be affected by hypoperfusion and direct viral injury, contributing to acute kidney injury. | |
Spleen involvement leads to immune dysregulation and impaired clearance of infected cells. | |
| Tissues | Vascular endothelium is critically involved in hemorrhagic manifestations due to viral-induced damage and increased permeability. |
Lymphoid tissue shows depletion and dysfunction, impairing adaptive immune responses. | |
| Cells | Macrophages serve as primary target cells for Lassa virus replication and dissemination. |
Dendritic cells are infected and impaired, leading to defective antigen presentation and immune evasion. | |
Endothelial cells are damaged, contributing to vascular leakage and hemorrhagic manifestations. | |
| Chemical Mediators | Interferon-alpha is produced in response to infection but often insufficient to control viral replication. |
Tumor necrosis factor-alpha (TNF-α) contributes to systemic inflammation and vascular permeability. | |
Interleukin-6 (IL-6) levels correlate with disease severity and systemic inflammatory response. |
Treatments
Pharmacological Treatments
Ribavirin
- Mechanism:
Inhibits viral RNA synthesis by acting as a nucleoside analog, reducing replication of Arenaviruses.
- Side effects:
Hemolytic anemia
Teratogenicity
Elevated liver enzymes
- Clinical role:
First-line
Non-pharmacological Treatments
Supportive care including fluid and electrolyte management to prevent shock and organ failure.
Isolation precautions to prevent nosocomial transmission of the highly contagious virus.
Monitoring and management of bleeding complications with blood products as needed.
Prevention
Pharmacological Prevention
No licensed vaccine is currently available for Lassa fever prevention.
Ribavirin prophylaxis may be considered in high-risk exposures but is not routinely recommended.
Experimental vaccines are under development but not yet approved.
Non-pharmacological Prevention
Avoidance of contact with Mastomys natalensis rodents, the natural reservoir.
Use of personal protective equipment when caring for infected patients.
Proper rodent control and sanitation measures in endemic areas.
Isolation of infected individuals to prevent nosocomial transmission.
Community education on avoiding exposure to rodent excreta and contaminated food.
Outcome & Complications
Complications
Hypovolemic shock due to severe hemorrhage and vascular leakage.
Multi-organ failure involving liver, kidneys, and lungs.
Severe neurological complications including encephalitis and seizures.
Permanent sensorineural deafness as a disabling sequela.
Secondary bacterial infections due to immune suppression.
| Short-term Sequelae | Long-term Sequelae |
|---|---|
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Differential Diagnoses
Hemorrhagic Fevers (Lassa Fever - Arenaviruses) versus Ebola Virus Disease
Hemorrhagic Fevers (Lassa Fever - Arenaviruses) | Ebola Virus Disease |
|---|---|
Exposure to multimammate rats in West Africa | Contact with infected primates or bats in Central and West Africa |
Arenavirus family, ambisense single-stranded RNA virus | Filovirus family, negative-sense single-stranded RNA virus |
Variable severity with fatality around 1-15% | Rapid progression with high fatality often >50% |
Positive RT-PCR for Lassa virus RNA | Positive RT-PCR for Ebola virus RNA |
Hemorrhagic Fevers (Lassa Fever - Arenaviruses) versus Dengue Fever
Hemorrhagic Fevers (Lassa Fever - Arenaviruses) | Dengue Fever |
|---|---|
Exposure to rodent excreta in rural West Africa | Recent mosquito bite in tropical urban areas |
Arenavirus, ambisense single-stranded RNA virus | Flavivirus, positive-sense single-stranded RNA virus |
Mild thrombocytopenia with elevated liver enzymes | Marked thrombocytopenia with hemoconcentration |
Prolonged febrile illness with multisystem involvement | Self-limited febrile illness with possible hemorrhagic complications |
Hemorrhagic Fevers (Lassa Fever - Arenaviruses) versus Yellow Fever
Hemorrhagic Fevers (Lassa Fever - Arenaviruses) | Yellow Fever |
|---|---|
Exposure to rodent reservoirs in West Africa | Recent travel to endemic areas with Aedes mosquito exposure |
Arenavirus transmitted by rodent excreta | Flavivirus transmitted by mosquitoes |
Elevated transaminases without prominent jaundice | Elevated bilirubin with jaundice and elevated transaminases |
Positive RT-PCR for Lassa virus RNA | Positive IgM serology or PCR for yellow fever virus |
Hemorrhagic Fevers (Lassa Fever - Arenaviruses) versus Crimean-Congo Hemorrhagic Fever
Hemorrhagic Fevers (Lassa Fever - Arenaviruses) | Crimean-Congo Hemorrhagic Fever |
|---|---|
Exposure to rodent excreta in West Africa | Tick bite or contact with livestock in Eastern Europe, Africa, or Asia |
Arenavirus, ambisense single-stranded RNA virus | Nairovirus, negative-sense single-stranded RNA virus |
Gradual onset with variable severity and lower mortality | Rapid onset hemorrhagic fever with high mortality |
Positive RT-PCR for Lassa virus RNA | Positive RT-PCR for Crimean-Congo hemorrhagic fever virus |
Hemorrhagic Fevers (Lassa Fever - Arenaviruses) versus Marburg Virus Disease
Hemorrhagic Fevers (Lassa Fever - Arenaviruses) | Marburg Virus Disease |
|---|---|
Exposure to multimammate rats in West Africa | Exposure to fruit bats or infected primates in Africa |
Arenavirus, ambisense single-stranded RNA virus | Filovirus, negative-sense single-stranded RNA virus |
Variable severity with slower progression | Severe hemorrhagic fever with rapid deterioration |
Positive RT-PCR for Lassa virus RNA | Positive RT-PCR for Marburg virus RNA |