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Globalization and high-speed means of transportation contribute to the spread of infections dangerous to humans. Airborne pathogens have pandemic potential as currently shown in case of the novel coronavirus SARS-CoV-2. Natural focal Lassa fever (LF) common in West African countries, in 35 cases was registered in non-endemic geographical areas because any person infected with Lassa virus (LASV) is a long-term source of infection (up to two months). Cases of person-to-person infection in endemic territories are described. In Germany, the facts of secondary virus transmission from patients to doctors have been recorded during the examination and blood collection from an apparently healthy person as well as during the autopsy of a deceased subjects due to severe LF course. Nonspecific malaise symptoms in LF are also characteristic of numerous other diseases common on the African continent, e.g., malaria and typhoid fever or viral infections such as yellow fever, Chikungunya, dengue and Zika, monkey pox and Ebola virus disease. In this regard, there may be similar dermatological manifestations. Timely detection of cases and differential diagnosis are crucial to ensure safe patient care and use of affordable antiviral therapy for LL provided by the drug Ribavirin. Research methods for studying LASV use polymerase chain reaction (PCR) for detecting viral RNA, electron microscopy, isolation of infectious virus cultured sensitive cells, indirect immunofluorescence reaction, enzyme immunoassay (ELISA) and immunochromatographic assays for the detection of antibodies and/or antigen as well as immunoblotting. Currently, test kits based on molecular and genetic methods are mainly used for LF laboratory diagnostics. Since the 1980s, ribavirin has been used to treat patients with LF. The serum accumulation of the drug in large quantities causes hemolysis, development of anemia and impaired renal function. In this regard, treatment options are being considered with decline in its concentration due to combined use with other antiviral drugs. A search for new therapeutic agents capable of inhibiting viral replication at disease early stage has been in progress due to lack of any approved vaccines.

Lassa fever is a natural focal disease dangerous for humans. In the larger part of sub-Saharan West Africa 37.7 million people in 14 countries live in areas where living conditions are suitable for zoonotic transmission of the virus from secretions of infected rodents of the species Mastomys natalensis. Routes of transmission can be via alimentary, airborne dust or airborne droplet pathways in case of accidental human contact with secretions of infected rodents. Mastomys natalensis penetrates into residence and place of storage of food and drinking water. In addition, the residents use such animals for food, so infection is also possible upon butchering carcasses. The etiological agent of this disease is the Lassa virus being one of the members of the Arenaviridae family. Unlike other arenavirus infections (e.g., Argentine and Bolivian fevers caused by Junin viruses and Machupo, respectively), human infection with Lassa virus can also occur from person to person. Cases of nosocomial infection among patients in conditions of poor hygiene and through contaminated medical equipment are described. Medical workers become infected during surgical operations or through contact with patients, because the pathogen can be transmitted via blood, saliva, vomiting, stool or urine. In endemic territories, Lassa fever is associated with significant morbidity, because 500 thousand clinical cases and due to 5 to 10 thousand fatal outcomes of this disease are registered annually (i.e. 12% mortality). The likelihood that this disease will become a more widespread threat worldwide may be associated with increased globalization as well as climate change leading to the expansion of the Lassa fever endemic zone into regions suitable for the settlement of M. natalensis and other rodent species capable of lifelong pathogen carriage. Among hospitalized persons with severe hemorrhagic symptoms, the mortality rate can be very high ranging from 14 to 89.5%. But in the majority of cases, the disease proceeds asymptomatically, and due to its long-term incubation period all ill subjects may be a source of infection, especially travelling at long distance by plane or train. Clinically evident disease occurs in the form of various nonspecific symptoms from malaise, fever, sore throat and chest, cough, myalgia and gastrointestinal disorders to signs of central nervous system disorders. The diagnosis of Lassa fever is often difficult due to the similarity of its course with other viral diseases common in Africa or malaria or typhoid fever. More specific symptoms for Lassa fever are revealed as conjunctivitis, hepatitis, pharyngitis, tonsillitis as well as developing oropharyngeal ulcers. Severe disease is complicated by abnormal bleeding, generalized edema, respiratory failure, hypotension, proteinuria, transaminitis, encephalopathy. Deafness develops in about 20% of cases. Multiple organ failure and open bleeding lead to death. The review is devoted to analyzing publications on the etiology, epidemiology and clinical picture of Lassa fever due to a threat of its importation with sick subjects to the territory of the Russian Federation.