Lassa virus

Lassa fever is caused by the Lassa virus, a member of the zoonotic Arenaviridae family. It is an enveloped, single-stranded, bisegmented RNA virus. The natural reservoir of Lassa virus is the Mastomys natalensis rodent (multimammate rat/mouse) that sheds the virus in urine and fecal droppings.

• Viruses; ssRNA viruses; ssRNA negative-strand viruses; Arenaviridae; Mammarenavirus ^[1]

• Lassa virus belongs to Arenaviridae.^[2]
• The Arenaviridae are a family of viruses whose members are generally associated with rodent-transmitted diseases in humans (zoonotic). Each virus usually is associated with a particular rodent host species in which it is maintained.

• Lassa virus is an enveloped, single-stranded, bisegmented, ambisense RNA virus.

• Lassa virus genome is contained in two RNA segments, each of which encodes 2 viral proteins (total 4 viral proteins)^[3][4]
  • The large segment encodes RNA polymerase (L) and a small zinc-binding protein (Z) that regulates transcription and replication^[5][6]
  • The small segment encodes the nucleoprotein (NP) and the surface glycoprotein precursor (GP or viral spike). The GP protein is cleaved into the envelope glycoproteins, GP1 and GP2, that bind to the alpha-dystroglycan receptor and mediate host cell entry^[7]
• Nucleotide studies of the genome have shown that Lassa has four lineages: Three in Nigeria and a fourth in Guinea, Liberia, and Sierra Leone. The Nigerian strains are thought to be ancestral to the others.^[8].

• The most common natural reservoir of Lassa virus is the rodent, Mastomys natalensis. Mastomys natalensis is commonly known as the “multimammate rat/mouse” due to the female’s multiple and prominent mammary glands.
• The mastomys rodents are abundant in the Savannas and forests of West, Central, and East Africa.
• Once infected, the rodent is able to excrete the virus in the urine and feces for an extended time period. Mastomys rodents breed frequently, produce large numbers of offspring, and commonly inhabit human homes with food storage. All of these factors contribute to the relatively efficient spread of Lassa virus from infected rodents to humans.

The images below display key features of the Lassa virus.

• 
  This transmission electron micrograph (TEM) demonstrates Lassa virus virions adjacent to host cell debris.Retrieved from the Public Health Image Library (PHIL), Centers for Disease Control and Prevention.^[10]
• 
  This highly magnified transmission electron micrograph (TEM) demonstrates ultrastructural details of 3 Lassa virus virions.Retrieved from the Public Health Image Library (PHIL), Centers for Disease Control and Prevention.^[10]
• 
  This transmission electron micrograph depicted eight virions (viral particles) of an Arenavirus.Retrieved from the Public Health Image Library (PHIL), Centers for Disease Control and Prevention.^[10]

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