Andes virus
Deep in the Americas, a silent threat lurks within the seemingly harmless long-tailed pygmy rice rat: the Andes virus. This stealthy pathogen is the primary cause of Hantavirus Pulmonary Syndrome in South America—a terrifying illness that progresses with chilling speed and carries a high fatality rate. Understanding this virus means delving into its unique biology, its hidden life within rodents, and its potentially controversial means of spread. Andes virus is the deadliest hantavirus in South America, causing Hantavirus Pulmonary Syndrome (HPS) with a case fatality rate of around 40%. The virus's segmented RNA genome allows it to evolve rapidly through a process called reassortment, making it highly adaptable. Unlike most hantaviruses, Andes virus is uniquely speculated to transmit from human to human, though scientific evidence for this remains contentious.
AI Summary
Deep in the Americas, a silent threat lurks within the seemingly harmless long-tailed pygmy rice rat: the Andes virus. This stealthy pathogen is the primary cause of Hantavirus Pulmonary Syndrome in South America—a terrifying illness that progresses with chilling speed and carries a high fatality rate. Understanding this virus means delving into its unique biology, its hidden life within rodents, and its potentially controversial means of spread.
- Andes virus is the deadliest hantavirus in South America, causing Hantavirus Pulmonary Syndrome (HPS) with a case fatality rate of around 40%.
- The virus's segmented RNA genome allows it to evolve rapidly through a process called reassortment, making it highly adaptable.
- Unlike most hantaviruses, Andes virus is uniquely speculated to transmit from human to human, though scientific evidence for this remains contentious.
The Andes Virus: A Silent Threat
Imagine an illness that begins innocuously—like a common cold or flu—only to accelerate into severe respiratory failure in just days. This is the grim reality of Hantavirus Pulmonary Syndrome, or HPS, and the Andes virus is its most common and devastating cause across South America.
First identified in Argentina and Chile in 1995, the Andes virus quickly garnered attention for its aggressive nature. While other hantaviruses exist, ANDV stands out for its particularly high case fatality rate, hovering around a sobering 40%.
A Rodent's Secret
At the heart of the Andes virus's ecology is a small, unassuming creature: the long-tailed pygmy rice rat. These tiny rodents, prevalent in rural Argentina and Chile, carry the virus without showing any symptoms themselves—a persistent, asymptomatic infection that makes them perfect, unwitting reservoirs.
In the wild, the virus spreads among rodents primarily through saliva, often exchanged during aggressive encounters or even simple grooming. This intricate dance of transmission ensures the virus's survival, silently circulating within its animal hosts.
Leap to Humans
Humans typically become infected when they inhale tiny airborne particles—aerosols—that contain rodent saliva, urine, or feces. Picture dust stirred up in a shed where infected rodents have been, and you have the primary route of transmission.
Less common, but still possible, are infections through direct bites or scratches from an infected rodent, or even by consuming food or water contaminated with their excretions. These varied pathways underscore the importance of minimizing contact with wild rodents.
Unpacking the Virus: Structure and Genome
The Andes virus itself is a marvel of microscopic engineering. It's a sphere-shaped particle, measuring between 80 to 160 nanometers in diameter, encased in a fatty lipid envelope stolen from its host cell. This envelope is studded with vital spike proteins.
These spike proteins, called Gn and Gc, are like tiny grappling hooks, extending about 10 nanometers from the surface. They’re crucial for the virus to attach to and enter new cells, with Gn forming the stalk and Gc the head of this molecular key.
Inside that envelope lies the virus's genetic blueprint: a genome composed of three segments of negative-sense, single-stranded RNA. These segments are elegantly coiled and encased in nucleoproteins, forming what's known as a ribonucleoprotein, or RNP, complex.
Each of these three segments—small, medium, and large—carries instructions for different viral components. The small segment encodes the nucleoprotein; the medium segment, the crucial Gn and Gc spike proteins; and the large segment, the viral RNA-dependent RNA polymerase (RdRp).
The Viral Hijack: Life Cycle
The infection begins when the Andes virus's spike proteins bind to specific receptors on the surface of human cells, particularly endothelial cells that line blood vessels, and macrophages—key immune cells.
Once attached, the virus is swallowed by the cell in a process called endocytosis, enclosed in a bubble-like compartment called an endosome. A drop in pH inside this endosome triggers a critical event: the viral envelope fuses with the endosome membrane, unleashing the viral RNA into the host cell's cytoplasm.
Now, the virus takes over. Its RdRp enzyme gets to work, transcribing the negative-sense RNA into messenger RNA (mRNA). This mRNA is then 'read' by the host cell's own ribosomes, essentially tricking the cell into producing viral proteins.
The virus even employs a clever trick called 'cap snatching,' stealing caps from the host's own mRNA to ensure its viral messages are efficiently translated. It then uses its RdRp to replicate its genome, making fresh copies of its RNA segments.
Finally, newly assembled viral components gather near the cell membrane. As new virions bud off from the cell, they acquire their lipid envelope—complete with fresh spike proteins—from the host cell membrane, ready to infect new cells and continue the cycle.
The Sickness it Causes: HPS
In humans, Andes virus infection manifests as Hantavirus Pulmonary Syndrome, an aggressive disease with three distinct phases. Symptoms typically appear 1 to 8 weeks after exposure, beginning subtly, often mimicking a common viral infection.
The initial 'prodromal' phase lasts a few days, bringing fever, muscle aches, headache, and sometimes gastrointestinal issues like nausea and vomiting. It's during this deceptive phase that the virus is quietly wreaking havoc beneath the surface.
Then comes the terrifying 'cardiopulmonary' phase. Fluid rapidly fills the lungs, oxygen levels plummet, and the heart struggles, leading to dangerously low blood pressure and cardiogenic shock. Respiratory failure sets in quickly, often requiring intensive care.
Diagnosis relies on observing these telltale symptoms and confirming the presence of viral nucleic acid, proteins, or specific antibodies. Treatment, regrettably, remains supportive—focused on oxygen supplementation and managing complications—as no specific antiviral drugs or vaccines exist.
Preventing infection remains the most effective strategy: avoiding or minimizing contact with rodents and their habitats is paramount. While repeated infections haven't been observed, suggesting potential lifelong immunity after recovery, the risk is simply too high to take lightly.
A Contested Mode of Spread
One of the most unique—and debated—aspects of the Andes virus is the claim of human-to-human transmission. This was first reported during an outbreak in El Bolsón, Argentina, in 1996, a rare distinction among hantaviruses, which are almost exclusively transmitted from rodents.
Subsequent outbreaks have also reported person-to-person spread, often within families or among individuals in close contact during the early, prodromal phase of illness. Reported routes included saliva, airborne droplets, and even breast milk or across the placenta.
However, a comprehensive systematic review in 2021 cast significant doubt on these claims, citing insufficient evidence and methodological flaws in earlier research. This scientific scrutiny highlights the critical need for robust data to confirm such a profound epidemiological finding.
The Virus's Adaptability
Like all viruses, Andes virus evolves primarily through mutations—small changes, insertions, or deletions in its genetic code. This constant tinkering allows it to adapt to its hosts and environment over time.
But its segmented genome offers an additional, potent evolutionary advantage: reassortment. If a single host cell is co-infected by two different strains of Andes virus, their genetic segments can mix and match, creating entirely new hybrid viruses. This genetic shuffling can lead to rapid adaptation and potentially altered virulence.
A Family Tree
The Andes virus belongs to the family Hantaviridae, a group of RNA viruses primarily hosted by rodents. Specifically, it's classified under the genus Orthohantavirus, and its species name is Orthohantavirus andesense.
Its taxonomic journey has seen a few changes since its discovery. Initially known simply as Andes hantavirus, it was later updated to Andes orthohantavirus, before settling on its current scientific name, reflecting a deeper understanding of its genetic relationships within the viral kingdom.
Article
Andes virus
Andes virus (ANDV) is the most common cause of hantavirus pulmonary syndrome (HPS) in South America. Andes virus is transmitted mainly by the long-tailed pygmy rice rat (Oligoryzomys longicaudatus). In its natural reservoir, ANDV causes an asymptomatic, persistent infection and is spread through excretions, fighting, and grooming. Humans can become infected by inhaling aerosols that contain rodent saliva, urine, or feces, as well as through bites and scratches. In humans, infection leads to HPS, an illness characterized by an early phase of mild and moderate symptoms such as fever, headache, and fatigue, followed by sudden respiratory failure. The case fatality rate from infection is high, at about 40%.
The genome of ANDV is about 12.1 kilobases (kb) in length and segmented into three negative-sense, single-stranded RNA (-ssRNA) strands. The small strand encodes the viral nucleoprotein, the medium strand encodes the viral spike protein, which attaches to cell receptors for entry into cells, and the long strand encodes the viral RNA-dependent RNA polymerase (RdRp), which replicates and transcribes the genome. Genome segments are encased in nucleoproteins to form ribonucleoprotein (RNP) complexes that are surrounded by a viral envelope that contains spikes emanating from its surface.
ANDV replicates first by binding to the surface of cells with its envelope spikes. Virus particles, called virions, are then taken into the cell by endosomes, where a drop in pH causes the viral envelope to fuse with the endosome, which releases viral RNA into the host cell. RdRp then transcribes the genome for translation by host cell ribosomes and produces copies of the genome for progeny viruses. New virions are assembled near the cell membrane, where virions bud from the cell membrane and use it to obtain their viral envelope and leave the cell.
ANDV was first discovered in 1995 in Argentina and in Chile later that year. More than a hundred cases of HPS caused by Andes virus occur each year, most of them in Argentina and Chile. Apart from the long-tailed pygmy rice rat, Andes virus has also been found in various other rodent species in South America, most commonly the long-haired grass mouse (Abrothrix longipilis). Human-to-human transmission of ANDV was first reported in 1996 and continual reports since then have been made that Andes virus can spread from person to person. There is, however, insufficient evidence of such transmission.
Genome
Andes virus
The genome of Andes virus is about 12.1 thousand nucleotides in length and segmented into three negative-sense, single-stranded RNA (-ssRNA) strands. The segments form into circles via non-covalent bonding of the ends of the genome. The small segment, about 1.87 kilobases (kb) in length, encodes the viral nucleoprotein and a non-structural protein that inhibits interferon production. The medium segment, about 3.67 kb in length, encodes a glycoprotein precursor that is cleaved into the two spike proteins Gn and Gc during virion assembly. The large segment, about 6.56 kb in length, encodes the viral RNA-dependent RNA polymerase (RdRp), which is responsible for transcribing and replicating the genome. The ends of each segment contain untranslated terminal regions (UTRs) that are involved in the replication and transcription of the genome.
Structure
Andes virus
Virions are mostly spherical or pleomorphic in shape and range from 80 to 160 nm in diameter. They contain a lipid envelope covered in spike proteins made of the two viral glycoproteins, Gn and Gc. The spike proteins extend about 10 nm out from the surface and are tetrameric, consisting of four copies each of Gn and Gc with helical symmetry, in which Gn forms the stalk of the spike and Gc the head. Spikes are arranged on the surface in a lattice pattern. Inside the envelope are the three genome segments, which are encased in nucleoproteins to form a ribonucleoprotein (RNP) complex. Attached to each RNP complex is a copy of RdRp.
Life cycle
Andes virus
ANDV primarily infects endothelial cells and macrophages. It enters cells by using β3-integrins as receptors. Virions are taken into a cell via an endosome. Once pH is lowered, the viral envelope fuses with the endosome, which releases viral RNA into the host cell's cytoplasm. The small segment is transcribed by RdRp first, then the medium segment, and lastly the large segment. Once the genome has been transcribed, RdRp snatches caps from host messenger RNA (mRNA) to create viral mRNA that is primed for translation by host ribosomes to produce viral proteins.
For replication of the genome, a complementary positive-sense strand is produced by RdRp. Copies of the genome are made from this complementery strand. Progeny RNA strands are then encapsidated by nucleoproteins. During replication, the glycoprotein is cleaved in the endoplasmic reticulum by the host signal peptidase during translation. This produces Gn at the N-terminus and Gc at the C-terminus of the protein. Spike proteins are expressed on the surface of the cell membrane. Viral RNPs are transmitted to the cell membrane where they bud from the surface, thereby obtaining their envelope as the new progeny virions leave the cell.
Evolution
Andes virus
The most common way that hantaviruses evolve is through mutations of individual nucleotides being inserted, deleted, or substituted. Because Andes virus has a segmented genome, it is possible for recombination and reassortment of segments to occur, whereby segments from different lineages mix in a single host cell and produce hybrid progeny.
Ecology
Andes virus
The long-tailed pygmy rice rat, the primary reservoir of Andes virus
Andes virus is carried mainly by the long-tailed pygmy rice rat (Oligoryzomys longicaudatus), a common species in rural Argentina and Chile. Apart from the long-tailed pygmy rice rat, Andes virus is relatively common in the long-haired grass mouse. Seroprevalence of ANDV in its hosts is found throughout South America, but is highest in Patagonia. Transmission of Andes virus between rodents appears to be primarily through saliva and aerosols that contain saliva. In its rodent hosts, it causes a persistent, asymptomatic infection. Transmission to humans occurs mainly through the inhalation of aerosols that contain mouse salivas, urine, or feces. Transmission can also occur through consumption of contaminated food, bites, and scratches.
Human-to-human transmission of Andes virus was first claimed to be a part of a 1996 outbreak in southern Argentina. Since then, there have been continual claims that it can spread from person to person. It can reportedly spread through saliva, airborne droplets from coughing or sneezing, breastmilk, from mother to child across the placenta, and through the digestive tract. Person-to-person transmission reportedly occurs mainly within families or when engaging in close activities with an infected person during the prodromal disease phase. A 2021 systematic review, however, found these claims not to be supported by sufficient evidence and cited flawed methodology in research on Andes virus outbreaks.
Disease
Andes virus
Andes virus infection usually causes hantavirus pulmonary syndrome (HPS), also called hantavirus cardiopulmonary syndrome (HCPS). Symptoms occur within 1–8 weeks after exposure to the virus and come in three phases: prodromal, cardiopulmonary, and recovery. Prodromal (early) symptoms last for a few days and include fever, muscle pain, headache, coughing, nausea, vomiting, chills, and dizziness. The cardiopulmonary phase lasts for several days and is characterized by fluid buildup in the lungs, low oxygen levels in the blood, elevated or irregular heart rate, low blood pressure, cardiogenic shock, and respiratory failure. The case fatality rate from ANDV infection is about 40%.
ANDV is the most common cause of HPS in South America, which predominantly occurs in Argentina, Brazil, and Chile. In Argentina, 100–200 cases occur each year. ANDV infection is diagnosed based on observation of symptoms and testing for hantavirus nucleic acid, proteins, or hantavirus-specific antibodies. Treatment is supportive in nature and includes supplementing oxygen during the cardiopulmonary phase. No vaccines exist for Andes virus infection, so the main way to prevent infection is to avoid or minimize contact with rodents. Repeated infections of hantaviruses have not been observed, so recovering from infection likely grants life-long immunity.
Classification
Andes virus
Andes virus is classified into the species Orthohantavirus andesense in the genus Orthohantavirus, which is in the family Hantaviridae, the family that all hantaviruses belong to. Other member viruses of Orthohantavirus andesense include the Castelo dos Sonhos virus, Lechiguanas virus, and Orán virus. The Chile-9717869 isolate of Andes virus is the exemplar virus of the species. This taxonomy is shown hereafter:
• Family: Hantaviridae • Genus: Orthohantavirus • Species Orthohantavirus andesense • Andes virus • Castelo dos Sonhos virus • Lechiguanas virus • Orán virus
History
Andes virus
Andes virus was first discovered in Argentina in 1995 and is named after the Andes mountain range. Cases were first reported in Chile that same year. Human-to-human transmission was first reported in an outbreak in 1996 in El Bolsón, Argentina. Since then, sporadic outbreaks with reported person-to-person transmission have occurred. Andes virus was accepted as a species by the International Committee on Taxonomy of Viruses in 1999 and has undergone a series of changes to its species name, first changing to Andes hantavirus, then Andes orthohantavirus, and most recently to the current Orthohantavirus andesense.