Lassa virus: A species of ARENAVIRUS, part of the Old World Arenaviruses (ARENAVIRUSES, OLD WORLD), and the etiologic agent of LASSA FEVER. LASSA VIRUS is a common infective agent in humans in West Africa. Its natural host is the multimammate mouse Mastomys natalensis.Lassa Fever: An acute febrile human disease caused by the LASSA VIRUS.Arenaviridae: A family of RNA viruses naturally infecting rodents and consisting of one genus (ARENAVIRUS) with two groups: Old World Arenaviruses (ARENAVIRUSES, OLD WORLD) and New World Arenaviruses (ARENAVIRUSES, NEW WORLD). Infection in rodents is persistent and silent. Vertical transmission is through milk-, saliva-, or urine-borne routes. Horizontal transmission to humans, monkeys, and other animals is important.Guinea: A republic in western Africa, south of SENEGAL and MALI, east of GUINEA-BISSAU. Its capital is Conakry.Arenaviruses, Old World: One of two groups of viruses in the ARENAVIRUS genus and considered part of the Old World complex. It includes LASSA VIRUS and LYMPHOCYTIC CHORIOMENINGITIS VIRUS, although the latter has worldwide distribution now.Arenavirus: The only genus in the family ARENAVIRIDAE. It contains two groups ARENAVIRUSES, OLD WORLD and ARENAVIRUSES, NEW WORLD, which are distinguished by antigenic relationships and geographic distribution.RNA Viruses: Viruses whose genetic material is RNA.Murinae: A subfamily in the family MURIDAE, comprising the Old World MICE and RATS.Arenaviridae Infections: Virus diseases caused by the ARENAVIRIDAE.Hemorrhagic Fevers, Viral: A group of viral diseases of diverse etiology but having many similar clinical characteristics; increased capillary permeability, leukopenia, and thrombocytopenia are common to all. Hemorrhagic fevers are characterized by sudden onset, fever, headache, generalized myalgia, backache, conjunctivitis, and severe prostration, followed by various hemorrhagic symptoms. Hemorrhagic fever with kidney involvement is HEMORRHAGIC FEVER WITH RENAL SYNDROME.Africa, Western: The geographical area of Africa comprising BENIN; BURKINA FASO; COTE D'IVOIRE; GAMBIA; GHANA; GUINEA; GUINEA-BISSAU; LIBERIA; MALI; MAURITANIA; NIGER; NIGERIA; SENEGAL; SIERRA LEONE; and TOGO.Sierra Leone: A republic in western Africa, south of GUINEA and west of LIBERIA. Its capital is Freetown.Pichinde virus: A species of ARENAVIRUS, one of the New World Arenaviruses (ARENAVIRUSES, NEW WORLD), causing a fatal infection in the cricetine rodent Oryzomys albigularis. Asymptomatic laboratory infection in humans has been reported.Vero Cells: A CELL LINE derived from the kidney of the African green (vervet) monkey, (CERCOPITHECUS AETHIOPS) used primarily in virus replication studies and plaque assays.Liberia: A republic in western Africa, south of GUINEA and east of COTE D'IVOIRE. Its capital is Monrovia.Arenaviruses, New World: One of two groups of viruses in the ARENAVIRUS genus and considered part of the New World complex. It includes JUNIN VIRUS; PICHINDE VIRUS; Amapari virus, and Machupo virus among others. They are the cause of human hemorrhagic fevers mostly in Central and South America.Virus Diseases: A general term for diseases produced by viruses.Nucleoproteins: Proteins conjugated with nucleic acids.Cercopithecus aethiops: A species of CERCOPITHECUS containing three subspecies: C. tantalus, C. pygerythrus, and C. sabeus. They are found in the forests and savannah of Africa. The African green monkey (C. pygerythrus) is the natural host of SIMIAN IMMUNODEFICIENCY VIRUS and is used in AIDS research.Virus Replication: The process of intracellular viral multiplication, consisting of the synthesis of PROTEINS; NUCLEIC ACIDS; and sometimes LIPIDS, and their assembly into a new infectious particle.Vaccinia virus: The type species of ORTHOPOXVIRUS, related to COWPOX VIRUS, but whose true origin is unknown. It has been used as a live vaccine against SMALLPOX. It is also used as a vector for inserting foreign DNA into animals. Rabbitpox virus is a subspecies of VACCINIA VIRUS.RNA, Viral: Ribonucleic acid that makes up the genetic material of viruses.Receptors, Virus: Specific molecular components of the cell capable of recognizing and interacting with a virus, and which, after binding it, are capable of generating some signal that initiates the chain of events leading to the biological response.Lymphocytic choriomeningitis virus: The type species of ARENAVIRUS, part of the Old World Arenaviruses (ARENAVIRUSES, OLD WORLD), producing a silent infection in house and laboratory mice. In humans, infection with LCMV can be inapparent, or can present with an influenza-like illness, a benign aseptic meningitis, or a severe meningoencephalomyelitis. The virus can also infect monkeys, dogs, field mice, guinea pigs, and hamsters, the latter an epidemiologically important host.Viral Proteins: Proteins found in any species of virus.Marburgvirus: A genus in the family FILOVIRIDAE consisting of one species (Lake Victoria marburgvirus) with several strains. The genus shows no antigenic cross-reactivity with EBOLAVIRUS.Virus Cultivation: Process of growing viruses in live animals, plants, or cultured cells.Virus Shedding: The expelling of virus particles from the body. Important routes include the respiratory tract, genital tract, and intestinal tract. Virus shedding is an important means of vertical transmission (INFECTIOUS DISEASE TRANSMISSION, VERTICAL).Antigens, Viral: Substances elaborated by viruses that have antigenic activity.Antibodies, Viral: Immunoglobulins produced in response to VIRAL ANTIGENS.