Lassa hemorrhagic fever.

Lassa hemorrhagic fever is an acute zoonotic natural focal viral disease characterized by the development of hemorrhagic syndrome, ulcerative necrotic pharyngitis, pneumonia, myocarditis, kidney damage and a high mortality rate. Synonym - Lassa fever.

ICD-10 code

A96.2. Lassa fever.

Epidemiology of Lassa hemorrhagic fever

The source and reservoir of the Lassa hemorrhagic fever pathogen is the Mastomys natalensis rat, which lives in most African countries near human habitation. The virus has also been isolated from other African rodents (M. erythroleucus, M. huberti). Animals release the virus into the environment with excrement and saliva.

Pathogen transmission mechanisms: aerosol, feco-oral, contact. Transmission routes: airborne, food, water, contact. Transmission factors: food products, water, and objects contaminated with rodent urine. Human infection in natural foci can occur by inhaling aerosol containing rodent excrement: drinking water from infected sources: insufficiently heat-treated meat of infected animals.

A sick person is a great danger to others. The main transmission factor is blood, but the virus is also contained in the patient's excreta. Infection occurs through airborne droplets, contact and sexually. The virus can be excreted by patients for up to a month or more. Infection occurs through microtrauma when the patient's blood or excreta gets on the skin. There are registered cases of medical personnel becoming ill when using instruments contaminated with the pathogen, performing surgical operations and autopsies.

Susceptibility is high. All population groups are sensitive to the pathogen, regardless of age and gender.

Post-infection immunity is intense and long-lasting, and repeated cases of the disease have not been described. In endemic areas, antibodies are detected in 10-15% of the population, indicating the possibility of asymptomatic or mild disease.

The peculiarity of the epidemic process is that the transmission of the pathogen from person to person by airborne route leads to the emergence of secondary intra-family outbreaks, as well as to the emergence of nosocomial outbreaks, accompanied by high mortality. In addition, it is possible to import Lassa fever to non-endemic countries and the emergence of a focus of the disease there with contact transmission of the pathogen. Lassa fever is widespread in the countries of West and Central Africa, south of the Sahara (Nigeria, Sierra Leone, Guinea, Liberia, Mozambique, Senegal, Mali, etc.).

The seasonality of Lassa hemorrhagic fever is not pronounced, the incidence is constant.

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What causes Lassa hemorrhagic fever?

Lassa hemorrhagic fever is caused by Lassa virus of the genus Arenavirus of the family Arenaviridae; it belongs to the Old World arenavirus complex LChM/Lassa. It has antigen relationship with other arenaviruses (causative agents of lymphocytic choriomeningitis and hemorrhagic fever of South America). The virus has a spherical capsid with a particle diameter of 50-300 nm, covered with a lipid membrane including glycoproteins (G1 and G2). The nucleocapsid consists of protein (N) and RNA, two fragments of which (L and S) encode the synthesis of virion components in the infected cell; there are no hemagglutinins. Pathogenic for some species of monkeys, white mice, guinea pigs. In Vero cell culture, virus replication is accompanied by a cytopathic effect. It is resistant to environmental factors. The infectivity of the virus in blood serum and mucous secretions does not decrease for a long time without special treatment. The virus can be inactivated by fatty solvents (ether, chloroform, etc.).

Pathogenesis of Lassa hemorrhagic fever

The entry points for the pathogen are the mucous membranes of the respiratory and digestive organs, damaged skin. At the site of virus introduction after its primary replication in the lymphoid elements, viremia develops with hematogenous dissemination of the pathogen, affecting many organs and systems. The virus has tropism for various human organ systems and causes necrotic changes in the cells of the liver, myocardium, kidneys, endothelium of small vessels, which determines the course of the disease. In severe cases, due to the cytopathic effect of the virus and cellular immune reactions, damage to endothelial cells in combination with impaired platelet function leads to increased "fragility" and permeability of the vascular wall. Deep hemostasis disorders occur with the development of disseminated intravascular coagulation syndrome and consumption coagulopathy.

Symptoms of Lassa hemorrhagic fever

The incubation period of Lassa hemorrhagic fever lasts 3-20 days, more often 7-14 days.

There is no generally accepted classification. There are mild, moderate and severe forms of the disease.

The onset of Lassa hemorrhagic fever is subacute or gradual. The following symptoms of Lassa hemorrhagic fever are identified: general malaise, moderate muscle and headaches, low fever, conjunctivitis. During this period, most patients (80%) develop a characteristic lesion of the pharynx in the form of ulcerative necrotic pharyngitis, as well as an increase in cervical lymph nodes. By the end of the first week of the disease, the body temperature reaches 39-40 C; symptoms of Lassa hemorrhagic fever increase: nausea, vomiting, chest and abdominal pain join in; diarrhea develops, leading to dehydration. From the second week, a maculopapular rash may appear: hemorrhagic manifestations are identified (subcutaneous hemorrhages, nasal, pulmonary, uterine and other bleeding). Bradycardia, arterial hypotension occur; hearing loss, seizures and focal neurological clinical manifestations are possible. In unfavorable cases, swelling of the face and neck occurs, free fluid is detected in the pleural and abdominal cavities, and hemorrhagic syndrome increases. In severe cases, death occurs on the 7th-14th day. In surviving patients, body temperature decreases lytically after 2-4 weeks. Recovery is slow. General weakness persists for several weeks, in some cases hair loss occurs and deafness develops; relapses of the disease are possible.

Complications of Lassa hemorrhagic fever

Pneumonia, myocarditis, acute renal failure, shock, acute psychosis.

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Mortality and causes of death

Mortality is 30-50% and higher (especially high in pregnant women in the third trimester). Causes of death: infectious-toxic shock, hypovolemic shock, acute renal failure, hemorrhagic syndrome.

Diagnosis of Lassa hemorrhagic fever

Early clinical diagnosis of Lassa fever is difficult, since there are no specific symptoms of Lassa hemorrhagic fever. Of the clinical manifestations, the most diagnostic value is: subacute onset; a combination of fever, ulcerative pharyngitis, hemorrhagic syndrome and renal failure. Of great importance are epidemiological data (stay in an epidemic focus) in combination with the results of virological and serological studies.

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Specific and non-specific laboratory diagnostics of Lassa hemorrhagic fever

Lassa hemorrhagic fever is diagnosed using virological and serological methods in special laboratories with biosafety level IV. The absolute diagnostic sign of the disease is the isolation of the virus from the patient's blood, throat swabs, saliva, urine and exudates (pleural, pericardial, peritoneal); as well as from the deceased - from samples of internal organs. Effective diagnostic methods: ELISA and RNIF. The diagnosis is confirmed serologically (with an increase in antibody titers to the Lassa virus by 4 times or more). The complement fixation reaction has a retrospective value.

Non-specific laboratory diagnostics of Lassa hemorrhagic fever includes a complete blood count (revealing leukopenia changing to leukocytosis, left shift in the neutrophil formula, thrombocytopenia, increased ESR); biochemical blood test (characterized by hypoproteinemia; increased aminotransferase activity, azotemia); determination of the coagulogram (characterized by hypocoagulation) and acid-base balance of the blood (signs of decompensated acidosis are expressed); general urine analysis (revealing proteinuria, hematuria, cylindruria).

Differential diagnosis of Lassa hemorrhagic fever

Differential diagnostics of Lassa hemorrhagic fever is carried out with diseases that occur with prolonged fever (typhoid and typhus, sepsis, malaria), diarrhea (viral diarrhea), hemorrhagic syndrome (other hemorrhagic fevers), leptospirosis, herp-angina, streptococcal pharyngitis, diphtheria, pneumonia.

Differential diagnosis of Lassa fever

Diseases	Similarities	Differences
Malaria	Headache, high fever, body and muscle aches. Jaundice and oliguria are possible.	Malaria does not cause ulcerative necrotic stomatitis, enlargement of peripheral lymph nodes, but unlike hemorrhagic fever, it is characterized by sweating, pallor, and an irregular fever (with tropical malaria). Hemorrhagic syndrome with malaria develops rarely and is expressed to a lesser extent than with Lasa fever.
HFRS	Muscle and headaches, high fever, hemorrhagic syndrome. scleritis, conjunctivitis. oliguria	With HFRS there is no pharyngitis, diarrhea, or repeated vomiting. Unlike Lassa fever, oliguria with HFRS develops from the second week of the disease against the background of normal temperature. In addition, with HFRS, from the first days of the disease there is severe weakness, dry mouth, and thirst.
Leptospirosis	High fever, headaches, myalgia, hemorrhagic manifestations. oliguria. conjunctivitis. scleritis. Jaundice is possible.	Leptospirosis is not characterized by ulcerative necrotic pharyngitis, abdominal pain, vomiting, diarrhea, cough, chest pain, relative bradycardia, leukopenia, often detected in Lassa fever

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Indications for consultation with other specialists

Differential diagnostics of Lassa hemorrhagic fever with diseases that have a similar clinical picture or that aggravate the course of hemorrhagic fever is carried out in parallel with the necessary consultations of relevant specialists: pulmonologist, gastroenterologist, nephrologist, neurologist, etc.

Indications for hospitalization

All patients are subject to hospitalization and strict isolation in specialized infectious disease departments of hospitals.

Treatment of Lassa hemorrhagic fever

Regime and diet

The patient requires strict bed rest and round-the-clock medical supervision.

A diet of semi-liquid, easily digestible food without limiting the amount of proteins and table salt is preferable, which corresponds to table No. 4 according to Pevzner.

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Drug treatment of Lassa hemorrhagic fever

Antiviral treatment of Lassa hemorrhagic fever is carried out by intravenous administration of ribavirin for 10 days (the initial dose of the drug is 2 g, then 1 g is administered every 6 hours for 4 days and 0.5 g every 8 hours for the next 6 days). In the early stages of the disease, convalescent plasma is used in a number of endemic regions.

Pathogenetic treatment of Lassa hemorrhagic fever is aimed at combating shock, hemorrhagic syndrome, cardiac and respiratory failure, as well as detoxification measures and infusion rehydration with saline solutions. Antibiotics are used for bacterial complications.

Clinical examination

Lassa hemorrhagic fever does not require outpatient observation.

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Patient information sheet

It is recommended to eat a complete diet using easily digestible products, without any special restrictions; adherence to a physical regimen.

Approximate periods of incapacity for work

In case of a favorable outcome, recovery is long. Given the severity of the disease, convalescents are considered incapacitated for 4-6 weeks after discharge from the hospital.

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How is Lassa hemorrhagic fever prevented?

Specific prophylaxis for Lassa hemorrhagic fever has not been developed.

Non-specific prevention of Lassa hemorrhagic fever consists of protecting premises from rodent penetration and deratization measures in natural foci. Medical personnel must be trained in caring for contagious patients and must work in protective clothing, respirators or gauze masks, gloves, and glasses. Strict isolation of patients is recommended (preferably in special plastic or glass-metal cabins with autonomous life support) for at least 30 days from the onset of the disease. Monitoring of persons who have been in contact with patients continues for 17 days. Final disinfection is carried out. For emergency prevention of Lassa fever, ribavirin is used (orally 0.2 g 4 times a day for 10 days). Quarantine measures are carried out for febrile patients arriving from Central and West Africa.

Lassa hemorrhagic fever prognosis

Lassa hemorrhagic fever has a serious prognosis. In severe cases, the mortality rate is high (up to 50% and higher). It decreases with timely comprehensive treatment. In mild and moderate cases, the prognosis is favorable. The recovery period is protracted.

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