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15 Cards in this Set
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Lassa Fever |
Lassa fever is a viral Haemorrhagic fever that may present as an acute condition with a high morbidity and mortality or in sub-clinical form with non-specific symptoms as fever, malaise and muscle pain.
It is a zoonosis and also a cause of hospital acquired infection |
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What is viral hemorrhagic fever |
Viral hemorrhagic fevers (VHFs) refer to a group of illnesses that are caused by several distinct families of viruses. In general, the term “viral hemorrhagic fever” is used to describe a severe multisystem syndrome (multisystem in that multiple organ systems in the body are affected). Characteristically, the overall vascular system is damaged, and the body’s ability to regulate itself is impaired. These symptoms are often accompanied by hemorrhage (bleeding); however, the bleeding is itself rarely life-threatening. |
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History of Lassa fever |
First described in the 1950’s but the virus was identified in January, 1969. The disease was first discovered in a town called Lassa (in Yedseram river valley at the South end of Lake Chad) in Borno State of Northern Nigeria during which time, two Missionary nurses (Laura wine (lassa mission hosp) and Charlotte Shaw (Evangel hosp., Jos) died of it. |
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Causative agent of Lassa fever |
The causative agent is the Lassa Fever Virus – a single stranded RNA virus of Arenaviridae family. Other VHF include: Ebola, Dengue, Hantan, Yellow fever, Rift valley fever, etc. |
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Epidemiology |
It is endemic but occurs in epidemic form sporadically in West Africa. Since the first case, outbreaks of varying intensity have occurred in Nigeria, and countries of Manu river basin like Sierra Leone, Guinea and Liberia. There are also reports in Ghana and Central Africa (Congo and Senegal). It is also the most commonly exported viral haemorrhagic fever (Germany, America and UK). The disease probably exists in other West African Countries as well since these rodents are present in the tropics. No age or sex variation has been demonstrated, but the effect is more severe in infants and pregnant women. |
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Incubation period |
Incubation period is 1 – 4 weeks (5-21 days) following exposure. |
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Reservoir agent |
The virus is transmitted by peri-domestic rodents (rats and mice) of the Mastomys Nataliensis Specie. Other species are also implicated in Sierra-Leone. Mastomys rodents breed very frequently, produce large numbers of off-springs, and are numerous in the savannas and forests of west, Central, and East Africa and readily colonize human homes. These factors together contribute to the relatively efficient spread of lassa virus from infected rodents (which occur at birth) to man. |
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Primary infection |
Primarily infection is from rodent to man through: ingestion of food or material contaminated by rodent excreta (urine or faeces), inhalation of aerosolized virus and catching and preparing mastomys for food. |
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Secondary infection |
Secondary infection of human-human is through direct contact with the blood, urine, faeces or other body fluids of a person with Lassa fever or indirectly from contaminated medical equipment and accidental inoculation. Sexual transmission remains controversial. |
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Signs and symptoms |
80% of cases – Asymptomatic, 20% associated with severe multi-systemic disease after incubation(5-21/7). Gradual onset of fever (38oC), headache, malaise and other non-specific signs and symptoms. Pharyngitis, myalgia, retro-sternal pain, cough and gastrointestinal symptoms .A minority present with classic symptoms of bleeding, neck/facial swelling Hypotension and shock. Signs of renal failure Neurological symptoms include tremors, convulsions and encephalitis. Deafness is a complication. IN CHILDREN: Signs and symptoms are most often similar to adults, but ‘’Swollen baby syndrome’’: Oedema/anarsaca, abdominal distension, bleeding. DURING PREGNANCY Particularly severe in pregnant women and their offspring. Breast and areola pain, tenderness, enlargement. |
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National case definition and guidelines |
NATIONAL CASE DEFINITION AND GUIDELINES Suspected case: illness with onset of fever and no response to the usual causes of fever in the area, with at least one of the following signs: bloody diarrhoea, bleeding gum, bleeding into the skin (purpura), bleeding into the eyes and blood in urine.Confirmed case: a suspected case with laboratory diagnosis (positive IgM antibody or viral isolation) or epidemiological link to confirmed case or outbreak. |
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Epidemic threshold for Lassa fever |
1 confirmed case |
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Laboratory confirmation |
•Most often diagnosed using ELISA techniques – detects IgM & IgG antibodies and Lassa antigen•Viral culture (7 to 10 days).•Post-mortem diagnosis via immune-histochemistry on tissue specimens•Detection of the virus via RT-PCR (majorly for research purposes) |
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Treatment |
1. Specific:Ribavirin at present is the only effective treatment, if started early within 6 days of symptom A. INTRAVENOUS INJ OF 100mg/1ml vials: 33mg/kg body wt stat, then: 16mg/kg body wt x 4 days, thereafter: 8mg/kg body wt x 6 days, total duration 10 days therapyB. PO (with food): 2gms Stat, then 1gm 6hrly for 4 days, then 0.5gm 8hrly for 7days, total duration of 10 days therapyC. Prophylaxis for close contacts: Give orally (each tablet 100mg/tab), 500mg 6hrly x 5 Days, total duration of 5 days.Patients are best treated in ICU’s for intensive care and strict infection control regulations.2. Supportive:Supportive treatment as appropriate: •Renal dialysis (as most patients die from acute renal and liver failure);•Blood transfusion : if Hb drops remarkably, as it usually causes hypovolaemic shock due to increased capillary permeability•Vitamin K: because of haemolysis and most times prolonged antibiotic use would have compromised the vitamin forming normal flora•Paracetamol •IV interferon therapy has also been used •At the critical stage careful fluid management is vital to avoid respiratory distress. Preferred fluid is haemaccel or ringer’s lactate•Monitor: urine output, serum E/U&Cr, LFT,FBC and clothing profile |
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Prevention and control |
1. At Community levelEffective measures include – use of rodent proof gauze, storing grains in rodent proof containers, disposing of garbage far from home, maintaining clean house-holds and keeping cats. Other measures will entail health education of the people on lassa fever, early diagnosis and treatment.2. At Hospital level•Health Education •Isolation of affected cases •Complete barrier nursing of cases •Application of universal precautions•Infection control policy with functional infection control team and committee•Notification of appropriate authority•Index case identification •Contact tracing •Regular surveillance of high risk contacts and maintenance of high index of suspicion among health care workers |
