Lassa fever is a naturally focal viral infection occurring with capillarotoxicosis and multiple organ disorders. Clinical manifestations of Lassa fever include fever, intoxication, diarrhea, bleeding, ulcerative pharyngitis, kidney failure, etc. Laboratory diagnostics of Lassa fever is based on the isolation of the virus from the biological materials of the patient, as well as the determination of antiviral antibodies using ELISA RPH, IFT. If Lassa fever is confirmed, rehydration, detoxification, antiviral therapy is performed; relief of hemorrhagic syndrome, correction of metabolic disorders, etc.
ICD 10
A96.2 Lassa fever
General information
Lassa fever is a hemorrhagic fever caused by the arenavirus of the same name and related to particularly dangerous infections with natural foci. The first cases of fever were registered in the medical staff of the hospital in Lassa (Nigeria) in 1969 in the form of an nosocomial infection. The name of the locality subsequently gave the name to the isolated virus and disease. Lassa fever is an endemic disease for the countries of West and Central Africa: 300-500 000 people get sick with hemorrhagic fever here every year. Imported cases of infection have been recorded in Europe, the USA, Israel, and Japan. The mortality rate from Lassa fever reaches 15-50%; infection is especially dangerous for pregnant women, since it leads to the death of the mother and fetus in 80% of cases.
Causes
Lassa fever is caused by a virus belonging to the Arenaviridae family, the Arenavirus genus. By its antigenic properties, it is close to other arenaviruses – pathogens of lymphocytic choriomeningitis and South American hemorrhagic fevers. Currently, 4 subtypes of Lassa virus have been identified, circulating in various regions. The virion has a spherical shape and a size of 70-150 nm; it is surrounded by a lipid envelope and contains RNA. The causative agent of Lassa fever is able to maintain its pathogenicity for a long time in biological environments, including when drying, however, it is sensitive to the effects of organic solvents (chloroform, ether).
The main carriers of infection are African rats of the genus Mastomys, which secrete the virus with saliva, urine and excrement. In the body of rodents, the virus can persist for life and is asymptomatic. In addition, the source of infection is a person with Lassa fever, all of whose secretions are contagious for the entire period of the disease. The spread of infection can occur by food and water through the use of food and water contaminated with the secretions of infected rats. It is also possible to be infected by airborne droplets (when inhaling dust particles with rodent excretions), by contact (when using contaminated household items, removing the skins of killed animals), sexually and vertically. Nosocomial cases of infection of medical staff with Lassa fever were caused by infection by aerogenic route and through microtrauma of the skin during parenteral interventions. Susceptibility to infection among the population is high, regardless of gender and age. Postinfectious immunity is long-lasting; cases of repeated infection with Lassa fever are not reported.
The entrance gates for the Lassa virus are the mucous membranes of the respiratory tract, gastrointestinal tract, conjunctiva, damaged skin. Once in the body, the virus multiplies in regional lymphoid elements, after which viremia and hematogenic dissemination of the pathogen develops with damage to the mononuclear phagocytic system. Damage to monocytes and a significant release of cytokines contributes to the development of infectious-toxic, hemorrhagic and DIC syndrome, multiple organ disorders. The tropicity of the virus to many organs and tissues causes necrotic changes in the endothelium of the vessels of the liver, kidneys, myocardium, etc.
Symptoms
The spectrum of clinical manifestations of Lassa fever is very variable: possibly inapparant, subclinical, manifest and lightning-fast course of infection. In the manifest form, the incubation period takes 7-14 days. The fever increases gradually and within a few days reaches 39-40 ° C. At this time, patients are concerned about general malaise, bruising, headache and muscle pain, conjunctivitis. In parallel with fever, 80% of patients develop angina or ulcerative necrotic pharyngitis.
By the end of the first week of the course of this disease, there are pains in the chest, back, abdomen; nausea, vomiting, watery diarrhea develops, quickly leading to dehydration. At the beginning of the second week of the disease, an exanthema of a spotty-papular petechial, erythematous character joins. At the same time, hemorrhagic manifestations develop: ecchymosis, nasal, gastrointestinal, pulmonary, uterine bleeding. Convulsions, meningeal symptoms, impaired consciousness, hearing loss may occur. Examination of patients with Lassa fever reveals dry skin and mucous membranes, cervical lymphadenitis, hepatomegaly, bradycardia, arterial hypotension. In the case of a favorable course of Lassa fever, a lytic decrease in temperature occurs after 2-3 weeks. Postinfectious asthenia persists for a long time, relapses of the infectious process are possible. Late complications include uveitis, deafness, alopecia, orchitis.
Severe course of Lassa fever is observed in about 30-50% of patients. In these cases, against the background of feverish intoxication and hemorrhagic syndrome, a picture of multiple organ lesions unfolds, including pneumonia, exudative pleurisy, myocarditis, pericarditis, hepatitis, ascites, serous meningitis, encephalitis, etc. Lethal outcomes are usually observed at the 2nd week of the disease from acute renal failure, infectious-toxic and hypovolemic shock, pulmonary edema and other causes. The course of Lassa fever is particularly severe in children under 2 years of age and pregnant women: in the latter, the disease almost always ends with intrauterine fetal death or maternal mortality. In this regard, the infection of a pregnant woman with Lassa fever serves as a direct indication for an artificial termination of pregnancy.
Diagnostics
The criteria for the clinical and epidemiological diagnosis of Lassa fever are a combination of fever, ulcerative pharyngitis, exanthema and hemorrhagic syndrome; stay in endemic foci, contact with patients. In the hemogram, leukocytosis and a sharp increase in ESR are noted; in the urine – proteinuria, leukocyturia, erythrocyturia, cylindrical. With the help of lung radiography, infiltrative changes and the presence of pleural effusion are detected. According to the ECG data, signs of diffuse myocardial damage are revealed.
Laboratory confirmation of the diagnosis of Lassa fever is the isolation of the virus from saliva, flushes from the throat, blood, urine, exudates, cerebrospinal fluid; determination of antiviral antibodies using ELISA, IFA, RPH, IFT; detection of RNA virus by PCR. In its course, Lassa fever is similar to many infectious diseases (streptococcal and herpetic sore throat, diphtheria, measles, SARS, malaria, other hemorrhagic fevers, typhoid fever, leptospirosis). Differential diagnosis is facilitated by examination of the patient by an infectious disease specialist, pulmonologist, gastroenterologist, nephrologist, neurologist, etc.
Treatment and prevention
If Lassa fever is suspected or confirmed, patients are hospitalized in infectious departments. Strict isolation of patients in special boxes and strict observance of anti-epidemic measures is mandatory. Etiotropic and vaccine preparations are under development, therefore, therapeutic measures are reduced to pathogenetic and post-syndrome therapy. The treatment is aimed at correcting metabolic acidosis, restoring BCC, and combating hemorrhagic syndrome. Detoxification measures and infusion rehydration, blood transfusions are carried out; vascular and respiratory analeptics, antipyretics, vitamins are introduced. In case of complications, antibiotics and glucocorticosteroids are used. In case of renal insufficiency, hemodialysis is indicated. Early initiation of antiviral therapy with ribavirin can reduce the severity of clinical manifestations of Lassa fever and reduce mortality. In some cases, a positive effect from the introduction of plasma convalescents was noted.
The prognosis is extremely serious: even with hospitalization and treatment, the mortality rate reaches 15%. To prevent epidemic outbreaks of Lassa fever, immediate organization of quarantine measures is necessary (isolation of patients and contact persons, burning of the corpses of the deceased, carrying out current and final disinfection in the hearth). Patients are subject to isolation for 30 days from the onset of the disease; contact persons – for 17 days (the maximum duration of the incubation period). Medical personnel caring for patients must comply with all the requirements of working with particularly dangerous infections (personal protection measures, anti-epidemic regime). Focal prevention of Lassa fever involves the fight against infection-carrying rats, the protection of food and water from contamination by rodent excretions.