Hemorrhagic fever Lossa

Lassa hemorrhagic fever is an acute zoonotic natural focal viral disease characterized by the development of hemorrhagic syndrome, ulcerative necrotic pharyngitis, pneumonia, myocarditis, renal damage and high mortality. The synonym is Lassa fever.

ICD-10 code

A96.2. Lassa fever.

Epidemiology of hemorrhagic fever Lossa

Source and reservoir of the causative agent of hemorrhagic fever Lassa is the rat Mastomys natalensis, which lives in most African countries near human habitation. The virus is also isolated from other African rodents (M. Erythroleucus, M. Huberti). Animals isolate the virus into the environment with excreta and saliva.

Mechanisms of transmission of the pathogen: aerosol, fecal-oral, contact. Transmission ways: airborne, food, water, contact. Transmission factors: food, water, as well as objects contaminated with urine rodents. Infection of people in natural foci can occur by inhaling an aerosol containing rodent excreta: drinking water from infected sources: insufficiently thermally processed 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 in this case occurs by airborne, contact and sexual routes. Isolation of the virus by patients can last up to a month or more. Infection occurs through micro-trauma when exposed to the skin of the blood or secretions of the patient. The cases of diseases of medical personnel with the use of tools contaminated with the pathogen, the conduct of surgical operations and the opening of corpses are recorded.

The susceptibility is high. To the causative agent all groups of the population are sensitive irrespective of age and sex.

Postinfectious immunity is tense and prolonged, repeated cases of the disease are not described. In endemic areas, antibodies are detected in 10-15% of the population, which indicates the possibility of asymptomatic or mild course of the disease.

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

Seasonality of hemorrhagic fever Lassa is not pronounced, incidence is constant.

[1], [2], [3],

What causes Lassa's hemorrhagic fever?

Lassa hemorrhagic fever is caused by Lassa virus of the genus Arenavirus of the Arenaviridae family; refers to a complex arenaviruses Old World LChM / Lassa. Has antigenic relationship with other arenaviruses (pathogens of lymphocytic choriomeningitis and hemorrhagic fever of South America). The virus has a spherical capsid, with a particle diameter of 50-300 nm, is coated with a lipid coat comprising glycoproteins (G1 and G2). Nucleocapsid consists of protein (N) and RNA, two fragments of which (L and S) code for the synthesis of the components of the virion in the infected cell; there is no hemagglutinin. Pathogen for some species of monkeys, white mice, guinea pigs. In Vero cell culture, viral replication is accompanied by a cytopathic effect. Resistant to environmental factors. The infectivity of the virus in the blood serum and mucous secretions without special treatment does not decrease for a long time. The virus can be inactivated with fatty solvents (ether, chloroform, etc.).

Pathogenesis of Lassa hemorrhagic fever

Entrance gate for the pathogen - mucous membranes of the respiratory and digestive organs, damaged skin. At the site of the introduction of the virus after its primary replication, lymphoid elements develop viralemia with hematogenous dissemination of the pathogen, the defeat of many organs and systems. The virus has tropism to various systems of human organs 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 responses, damage to endothelial cells in combination with impaired platelet function leads to increased "fragility" and permeability of the vascular wall. There are deep disorders of hemostasis with the development of the syndrome of disseminated intravascular coagulation and consumption coagulopathy.

Symptoms of hemorrhagic fever Lossa

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

A generally accepted classification does not exist. Allocate: mild, moderate, and severe course of the disease.

The beginning of hemorrhagic fever Lassa subacute or gradual. The following symptoms of hemorrhagic fever of Lassa are revealed: general malaise, moderate muscular and headaches, low fever, conjunctivitis. During this period, the majority of patients (80%) develop a characteristic defeat of pharynx in the form of ulcerative necrotic pharyngitis, as well as an increase in the cervical lymph nodes. By the end of the first week of the disease, the body temperature reaches 39-40 C; the symptoms of Lassa's hemorrhagic fever increase : nausea, vomiting, pains in the chest and stomach; develops diarrhea, leading to dehydration. From the second week, the appearance of a patchy-papular rash is possible: hemorrhagic manifestations (subcutaneous hemorrhage, nasal, pulmonary, uterine and other bleedings) are revealed. There is a bradycardia, arterial hypotension; possibly a decrease in hearing, the appearance of seizures and focal neurological clinical manifestations. In case of unfavorable course of the disease, there is swelling of the face and neck, reveals a free fluid in the pleural and abdominal cavities, increases hemorrhagic syndrome. In severe cases, death occurs on the 7-14th day. In surviving patients after 2-4 weeks, body temperature is lytically reduced. Recovery is slow. Within a few weeks, general weakness persists, in some cases hair falls and deafness develops; possible relapse of the disease.

Complications of Lassa hemorrhagic fever

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

[4], [5], [6], [7], [8],

Mortality and causes of death

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

Diagnosis of Lossa hemorrhagic fever

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

[9], [10], [11], [12]

Specific and nonspecific laboratory diagnostics of hemorrhagic fever Lassa

Diagnosis of hemorrhagic fever Lassa is carried out using virological and serological methods in special laboratories with IV level of biological safety. Absolute diagnostic sign of the disease is the isolation of the virus from the blood, flushing from the pharynx, saliva, urine and exudates (pleural, pericardial, peritoneal) patient; as well as from the dead - from internal organs. Effective methods of diagnosis: ELISA and RNIF. The diagnosis is confirmed serologically (with increasing titres of antibodies to the Lassa virus 4 times or more). The formulation of the complement fixation reaction is retrospective.

Nonspecific laboratory diagnosis of hemorrhagic fever Lassa includes a general blood test (detect leukopenia with a change in leukocytosis, a shift of the neutrophilic formula to the left, thrombocytopenia, increased ESR); biochemical blood analysis (hypoproteinemia, increased activity of aminotransferases, azotemia); definition of coagulogram (characteristic hypocoagulation) and acid-base state of blood (signs of decompensated acidosis are expressed); general analysis of urine (identify proteinuria, hematuria, cylindruria).

Differential diagnosis of hemorrhagic fever Lossa

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

Differential diagnosis of Lossa fever

Diseases	Similarities	Differences
Malaria	Headache, temperature rise to high values, body aches and muscles. There may be jaundice and oliguria	With malaria there is no ulcerative necrotic stomatitis. The increase in peripheral lymph nodes, but unlike hemorrhagic fever for it is characterized by sweating pallor irregular nature of fever (with tropical malaria). Hemorrhagic syndrome with malaria develops rarely and is less pronounced than with LAS fever
HFRS	Muscle and headaches, high fever hemorrhagic syndrome. Scleritis, conjunctivitis. Oliguria	With HFRS, there is no pharyngitis of diarrhea, multiple vomiting. In contrast to Lassa fever, oliguria with HFRS develops from the second week of the disease against a background of normal temperature. In addition, with HFRS from the first days of the disease there is a sharp weakness, dry mouth and thirst
Leptospirosis	High fever headaches myalgia, hemorrhagic manifestations. Oliguria. Conjunctivitis. Sclerite. Possible jaundice	For leptospirosis, ulcerative necrotic pharyngitis of abdominal pain, vomiting of diarrhea, cough, and pain in the chest are not characteristic. Relative bradycardia, leukopenia, often seen with Lassa fever

[13], [14], [15], [16], [17], [18]

Indications for consultation of other specialists

Differential diagnosis of hemorrhagic fever Lassa with diseases that occur with a similar clinical picture or aggravating the course of hemorrhagic fever is conducted in parallel with the necessary consultations of the appropriate specialists: pulmonologist, gastroenterologist, nephrologist, neurologist, etc.

Indications for hospitalization

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

Treatment of hemorrhagic fever Lassa

Diet and diet

The patient needs strict bed rest and 24-hour medical supervision.

A diet of semi-liquid, easily digestible food is preferred, without limiting the amount of protein and table salt, which corresponds to Pevzner's table No. 4.

[19], [20], [21]

Medicamentous treatment of hemorrhagic fever Lossa

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

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

Clinical examination

Lassa's hemorrhagic fever does not require follow-up.

[22], [23], [24], [25], [26], [27], [28], [29],

Memo for the patient

Recommended full-fledged food using easily digestible products, without special restrictions; compliance with the physical regime.

Approximate terms of incapacity for work

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

[30],

How is Lassa hemorrhagic fever prevented?

Specific prevention of hemorrhagic fever Lassa is not developed.

Nonspecific prophylaxis of Lassa hemorrhagic fever consists in protecting the premises from the penetration of rodents and deratization activities in natural foci. Medical personnel should be trained to care for infectious patients and must work in protective clothing, respirators or gauze masks, gloves, goggles. Recommended strict isolation of patients (preferably in special plastic or glass-metal cabins with autonomous life support) for a period of at least 30 days from the onset of the disease. Monitoring of persons in contact with patients continues for 17 days. Conduct final disinfection. For emergency prevention of Lassa fever, ribavirin is used (inside 0.2 g 4 times a day for 10 days). Carry out quarantine measures for febrile patients who arrived from the countries of Central and West Africa.

Forecast of hemorrhagic fever Lassa

Hemorrhagic fever Lassa has a serious prognosis. In case of severe disease, lethality is high (up to 50% and higher). Reduced in the conduct of timely comprehensive treatment. With a light and moderate flow forecast favorable. The period of convalescence is protracted.

[31], [32], [33],