VIRAL HAEMORRHAGIC FEVER: LASSA FEVER

Question 1

What is Lassa fever?
What are the 4 VHF’s?

Answer 1

Lassa fever is one of the agents of Viral hemorrhagic fevers (VHFs), a group of febrile illnesses caused by enveloped RNA viruses from several viral families.

The 4 viral families known to cause VHF disease in humans include: Arenaviridae (Lassa fever), Bunyaviridae (Hantavirus), Filoviridae (marburg, Ebola), and Flaviviridae (Yellow fever, Denge).

They are highly infectious, leading to potentially lethal disease syndrome characterized by fever, malaise, bleeding, edema, and hypotension.

Lassa fever, a member of arenaviruses first appeared in Lassa, Nigeria, in 1969 and has been found in all West Africa countries
Lassa fever may accounts for 5-14% of hospitalized febrile illnesses. The natural reservoir is a small rodent whose virus-containing excreta is the source of transmission.

Question 2

Features of Lassa fever

Answer 2

Lassa fever virus, a member of the Arenaviridae family
They are enveloped with circular single stranded ambi-sense segmented RNA virus possessing helical symmetry

Question 3

Pathophysiology of Lassa fever

Answer 3

1. The primary defect in patients with viral hemorrhagic fever (VHF) is that of increased vascular permeability which is thought to be secondary to pronounced macrophage involvement, widespread T-cell activation, resulting in multiple cytokine activation leading to increased vascular permeability and shock.
2. Inadequate or delayed immune response to viral antigens may lead to rapid development of overwhelming viremia.

Hemorrhagic complications are multifactorial: hepatic-zone 2 necrosis , consumptive coagulopathy, marrow injury to megakaryocytes.

Multisystem organ failure affecting the hematopoietic, neurologic, and pulmonary systems often accompanies the vascular involvement.

Vascular instability and bleeding abnormalities leads to cutaneous findings such as flushing, petechiae, purpura, ecchymoses, and edema.

Question 4

Risk factors and Clinical features of Lassa fever
Incubation period

Answer 4

• History of travel to tropical or rural areas, such as West Africa (Lassa fever)
• Contact with potential rodent reservoirs.
• Direct contact with rodents infected with hemorrhagic fever viruses is not necessary for transmission of infection, since aerosolized excreta may transmit infection.
• Contacts of patients with known viral hemorrhagic fever (VHF), especially family members or health care workers caring for infected patients, are at risk for infection if appropriate barrier precautions are not used
• Transmission of VHF has occurred from the reuse of unsterile needles and syringes used for treatment of infected patients
• Transmission of VHF also has occurred to individuals handling the deceased in preparation for burial or to individuals involved in the slaughter of infected livestock (as in RVF or CCHF).
• Incubation periods varies from 2-21 days.
• The initial symptoms correspond to development of viremia and include:
  High fever
  Headache
  Fatigue
  Abdominal pain
  Myalgias and
  Prostration.

With progression, there may be Hematemesis and bloody diarrhea

Generalized mucous membrane hemorrhage, Rash, Altered mental status and cardiovascular collapse (pre-terminal events)

Lassa fever virus results in the greatest amount of edema of any of the hemorrhagic fever viruses with no bleeding abnormalities present.
In severe cases, hemorrhage exudes from mucous membranes, venipuncture sites, and body orifices.

Question 5

Management of Lassa fever
What’s the mainstay therapy?
What are some safety measures?
What is recommended for postexposure prophylaxis?

Answer 5

Viral hemorrhagic fever (VHF) is a reportable disease.

Fluid & and electrolyte balance and other supportive therapy are the mainstay in therapy.

Give blood and blood products as clinically indicated.

Avoid I.M injections and the use of aspirin or other anticoagulants.

Minimize invasive procedures because of the risk associated with viral transmission from sharp objects.

Barrier nursing: Place patients in a private room and restrict entry to only essential staff; all staff entering the room should wear gloves and gowns.

Before exiting the room, discard all used protective barriers and clean shoes with a disinfectant like hypocloride.

Lassa fever have been treated effectively with intravenous and oral ribavirin.
Ribavirin has been recommended as a potential treatment for other arenaviruses and bunyaviruses.

Treatment is most effective when given early in the clinical course.

Ribavirin also is recommended for postexposure prophylaxis.

Question 6

Prevention of Lassa fever

Answer 6

• Efforts have been made in West Africa to educate people in high-risk areas about ways to decrease rodent populations, thereby reducing transmission of Lassa fever.
• Strict barrier precautions in the treatment of patients with known or suspected viral hemorrhagic fever infection reduce nosocomial transmission.
• Development of a Lassa virus vaccine is ongoing.

Question 7

Complications of Lassa fever

Answer 7

Complications from viral hemorrhagic fever (VHF) infection include:
retinitis
orchitis
encephalitis
hepatitis
transverse myelitis
and uveitis.

In patients who recover from Lassa fever infection, deafness is the most common complication. Spontaneous abortion also is common.

Question 8

Lab studies

Answer 8

Because of risks associated with handling infectious materials, perform the minimum necessary laboratory testing for diagnostic evaluation and patient care is needed.

Leukopenia and thrombocytopenia may be absent in Lassa fever, elevated hepatic transaminases are predictive of high mortality

Prothrombin time, activated partial thromboplastin time, international normalized ratio, and clotting times are prolonged.

A disseminated intravascular coagulation profile including fibrinogen level, fibrin degradation products, and platelet count may be useful.

In containment laboratories, serologic tests such as enzyme-linked immuno-sorbent assay (ELISA),
Polymerase chain reaction (PCR) and
Tissue cultures.