Torovirus

Key takeaways

Torovirus belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Torovirus to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Torovirus from memory before moving on to harder problems.

Reference excerpt

Torovirus is a genus of enveloped, positive-strand RNA viruses in the order Nidovirales and family Tobaniviridae. They primarily infect vertebrates, especially cattle, pigs, and horses. Diseases associated with this genus include gastroenteritis, which commonly presents in mammals. Torovirus is the only genus in the monotypic subfamily Torovirinae. The discovery of the first torovirus can be traced back to 1970s. Equine torovirus (EToV) was accidentally found in the rectal sample from a horse who was experiencing severe diarrhea. The 'Breda' bovine torovirus was later found in 1979 while investigation in a dairy farm in Breda. They had several calves experiencing severe diarrhea for months. In 1984, torovirus-like particles were detected with electron microscope (EM) technique in the human patients with gastroenteritis.

Virology

Taxonomy Until recently, the toroviruses were not assigned any family. The recent molecular analysis of the virus revealed its similarities with Arterivirus and coronaviruses, which led to the inclusion of the Torovirus along with the Arterivirus in the previously monogeneric Coronaviridae. At present, toroviruses are included in the order Nidovirales sub family Torovirinae, family Tobaniviridae. Resemblance, molecular and genetic similarities, virion dimensions, behavioral ties and other characteristic similarities and differences are observed by the researchers for the taxonomic classification of the virus. In the toroviruses, the Berne virus has been extensively studied at the molecular level as compared to its other members. In 1992, the International Committee on Taxonomy of Viruses ICTV got enough data to consider torovirus in the coronavirus family due to the similarities in structure, replication behavior and the genetic sequencing. The genus has the following subgenera and species:

Subgenus: Bantovirus Torovirus banli Subgenus: Renitovirus Torovirus bovis, Bovine torovirus Torovirus equi, Equine torovirus Torovirus suis, Porcine torovirus

Structure

Toroviruses (ToV) are single-stranded RNA viruses that have a peplomer-bearing envelope that is often correlated with the enteric infections in cattle and possibly humans. These viruses appear to occur globally, occurrence of ToVs have been reported from countries in various continents like Europe, Americas, New Zealand and South Africa. Torovirus particles typically possess a helical and symmetrical nucleocapsid that is coiled into a hollow cylindrical shape. The diameter is approximately 23 nm with an average length of 104 nm, where every turn cycle is at intervals of 4.5 nm. ToVs are pleomorphic, with size ranging from 100 nm to 150 nm with club-like outgrowths extending from the capsid. A nucleocapsid that is doughnut-shaped with helical symmetry is also discovered in Toroviruses. Among various species of the Toroviruses, only equine torovirus (EToV) can be grown in the cell culture medium due to which EToVs have been most extensively studied. The information from immunofluorescence studies and morphology of the bovine Toroviruses (BToV) intestinal cells has shown similarities among the EToVs and BToVs. Torovirus share some common characteristics with members of the related family Coronaviridae as they are round, pleomorphic, enveloped viruses about 120 to 140 nm in diameter.

Genome

Toroviruses have a single piece of single-stranded, positive-sense RNA. The total length is approximately 25-30kb and they possess a complex replication mechanisms that includes the use of subgenomic mRNA, ribosomal frameshifting, and polymerase stuttering. The genomic length of bovine torovirus is approximately 28.5 kb that is mainly comprised by one gene, replicase gene (20.2 kb). This gene contains two open reading frames, ORF1a and ORF1b that encodes proteins pp1a and pp1b. The first genomic sequence of the PToV (porcine torovirus) was done in Shanghai, China in 2014. Genome length of porcine Torovirus was found to be 28301 bp and possess 79% sequence identity with the bovine Torovirus genome.

Life cycle

Cattle, pig, and horse serve as the natural host of Toroviruses and infection is thought to be via the faecal-oral route. The Torovirus genome encodes for various structural proteins like spikes (S), membrane proteins (M), haemagglutinin‐esterase (HE) and nucleocapsid (N) which provides them the structural characterization necessary for infection and completing their life cycle. The first three proteins coding regions are deleted in the BEV species which enables them to grow in the cell culture, while other species are unable to grow in cell culture. The initial two-thirds of the torovirus genome has two open reading frames, ORF1a and ORF1b. ORFb1 encloses a domain that encodes for the enzymes such as RNA dependent RNA polymerase (RdRp) and the helicase (Hel) that are necessary for transcription and translation of the virus. Life cycle of Toroviruses involves replication within the infected host cell. These viruses predominantly bud into the lumen of the Golgi cisternae in the cytoplasm. EToV can be seen within various parts of the Golgi apparatus and in the extracellular regions as well. The nucleocapsids of these viruses in the extracellular region has characteristic torus shape, whereas these nucleocapsids are rod shaped prior to budding to the host cell, which points to some morphological change happening in the maturation stage of the virus. Moreover, the nucleocapsids of the BToV and EToV are also found to accumulate in the nucleus of the infected cell.

Clinical signs and diagnosis In cattle, the disease causes diarrhoea and systemic signs such as pyrexia, lethargy and anorexia. In calves, it may cause neurological signs and lead to death in some cases. Many diagnostic techniques for torovirus infection in clinical specimens are now available such as hemagglutination (HA), enzyme-linked immunosorbent assay (ELISA), immune electron microscopy, hemagglutination-inhibition tests (HA/HI), and nucleic acid hybridization. Mostly torovirus infecting humans are probably closely related to BRV or BEV and relate to any previous history of some enteric disease or infection. It is also the reason that the molecular techniques are considered more promising than the serological assays. Pigs can be infected without showing any signs and symptoms that are physically visible. Diagnosis of the viral infection involves electron microscopy, ELISA or haemagglutination inhibition.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Torovirus

Start with the simplest possible case. Write down what Torovirus claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Torovirus before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Torovirus ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Torovirus

In research: Torovirus appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Torovirus in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Torovirus is common in secondary-school and first-year university syllabi. It links to neighbouring topics Torovirinae, Virus genera, so understanding it makes those chapters shorter.
In everyday life: Look for Torovirus outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Torovirus in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Torovirus means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Torovirus out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Torovirus in simple terms?

Torovirus is a genus of enveloped, positive-strand RNA viruses in the order Nidovirales and family Tobaniviridae. They primarily infect vertebrates, especially cattle, pigs, and horses.

Why does Torovirus matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Torovirus?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Torovirus.