Epidemiology,Causes,Clinical manifestation and Management Of Lassa Fever

LASSA FEVER

  • Lassa fever is an acute viral hemorrhagic fever caused by the Lassa virus and first described in 1969 in the town of Lassa, in Borno StateNigeria; when 2 missionary nurses died of the disease.
  • Lassa virus is a member of the Arenaviridaevirus Similar to ebola, clinical cases of Lassa fever had been known for over a decade, but had not been connected with a viral pathogen.

       EPIDEMIOLOGY

  • Lassa fever is an endemic disease in portions of West Africa. It is recognized in Nigeria, Liberia, Sierra Leone, as well as Guinea.
  • However, because the rodent species which carry the virus (mastomys natalensis) are found throughout West, Central and East Africa, the actual geographic range of the disease may extend to other countries in these regions.
  • The number of Lassa virus infections per year in West Africa is estimated at 100,000300,000, with approximately 5,000 Unfortunately, such estimates are crude, because surveillance for cases of the disease is not uniformly performed.
  • In some areas of Sierra Leone and Liberia, it is known that 10%-16% of people admitted to hospitals have Lassa fever, which indicates the serious impact of the disease on the population of this region.
  • In these rodents, infection is in a persistent asymptomatic state. The virus is shed in their excreta (urine and feces), which can be aerosolized.
  • Infection in humans typically occurs by exposure to animal excreta through the respiratory or gastrointestinal tracts. Inhalation of tiny particles of infectious material (aerosol) is believed to be the most significant means of exposure.
  • It is possible to acquire the infection through broken skin or mucous membranes that are directly exposed to infectious material.
  • Transmission from person to person has also been established, presenting a disease risk for healthcare workers. Frequency of transmission by sexual contact has not been established.
  • In some African communities, they eat these rodents as a delicacy.

CLINICAL FEATURES

  • About 80% of infections with lassa virus are asymptomatic; meaning that only 20% of infected people, after the 21 days incubation period, develop clinical disease.
  • Non-specific symptoms include fever, facial swelling, muscle fatigue, conjunctivitis and mucosal bleeding.
  • Gastrointestinal tract
  • Nausea
  • Vomiting (bloody)
  • Diarrhea (bloody)
  • Abdominal pain
  • Constipation
  • Dysphagia (difficulty swallowing)
  • Hepatitis
  • Cardiovascular system
    • Pericarditis
    • Hypertension
    • Hypotension
    • Tachycardia (abnormally high heart rate)
  • Respiratory tract
    • Cough
    • Chest pain
    • Dyspnoea
    • Pharyngitis
    • Pleuritis
  • Nervous system
    • Encephalitis
    • Meningitis
    • Unilateral or bilateral hearing deficit
    • Seizures
  • Clinically, Lassa fever infections are difficult to distinguish from other viral hemorrhagic fevers such as Ebola and Marburg, and from more common febrile illnesses such as malaria.
  • In infected people, the virus is excreted in urine for 3-9 weeks and in semen for 3 months.

DIAGNOSIS

  • An ELISA test for antigen and IgM antibodies give 88% sensitivity and 90% specificity for the presence of the infection. From studies in Nigeria, 20% of people sampled tested positive to lassa virus; meaning they have been exposed to it at least.
  • Other laboratory findings in Lassa fever include:
  • Lymphopenia
  • Thrombocytopenia
  • Low aspartate aminotransferase levels in the blood.

Lassa fever virus can also be found in cerebrospinal fluid

TREATMENT

  • Resuscitation (C.A.B.D)
  • Ribavirin (early administration is key, IV preferrable) prevents virus replication.
  • Symptomatic treatment (anti-emetic, diarrhea medications, analgesics, anti-convulsants, antibiotics for possible superimposed bacterial infections etc).
  • Blood transfusion (if PCV <20% or a bit above, but with continuous bleeding and /or severe thrombocytopenia
  • Pregnant women with the disease should be induced to deliver, because the virus has high affinity for highly vascularized tissues like the placenta.
  • Also, regardless of quality of management, a term baby born to a lassa virus infected mother only has a 10% chance of survival.
  • Hence, emphasis is usually on saving the mother.

PROGNOSIS

  • About 15-20% of hospitalized Lassa fever patients will die from the illness.
  • The overall mortality rate is estimated to be 1%, because only 20% of people infected with the virus develop the disease.
  • But during epidemics, mortality can climb as high as 50%.
  • The mortality rate is greater than 80% when it occurs in pregnant women during their third trimester.
  • Because of treatment with ribavirin, fatality rates continue to decline.

PREVENTION

  • Control of rodents– fumigation, biological control (cats) etc.
  • Environmental hygiene– proper waste disposal, closed drainages
  • Isolation, early diagnosis and adequate treatment of cases– can prevent epidemics.
  • Food hygiene– proper storage, handling and processing.
  • Gloves, face masks, laboratory coats and goggles should be worn by care givers.
  • Researchers are still working on a vaccine, with promising results.

CONCLUSION

  • In conclusion, lassa fever is a disease mainly affecting poor people in their unhygienic rodent infested environment.
  • Early accurate diagnosis, with adequate care and administration of IV ribavirin, to isolated patients is key to prevention of death and epidemics.

Environmental hygiene and rodent control are crucial to prevention of lassa fever.

 

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