biology

Porcine reproductive and respiratory syndrome virus 2

Porcine reproductive and respiratory syndrome virus 2 is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Porcine reproductive and respiratory syndrome virus 2 rather than just read about it. In short: Porcine reproductive and respiratory syndrome virus 2 (Betaarterivirus americense) is a species of enveloped, positive-strand RNA viruses which infect domestic pigs. It is one of two porcine reproductive and respiratory syndrome viruses (PRRSV).

Key takeaways

Porcine reproductive and respiratory syndrome virus 2 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Porcine reproductive and respiratory syndrome virus 2 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Porcine reproductive and respiratory syndrome virus 2 from memory before moving on to harder problems.

Reference excerpt

Porcine reproductive and respiratory syndrome virus 2 (Betaarterivirus americense) is a species of enveloped, positive-strand RNA viruses which infect domestic pigs. It is one of two porcine reproductive and respiratory syndrome viruses (PRRSV). The two types of PRRSV are distinguished by which genomic cluster they are associated with. Type 1 is associated with a LV cluster. Type 2 is associated with a VR2332 cluster. PRRSV is in the Arteriviridae family and the order Nidovirales. It has a positive sense RNA genome that is 15 kb long. This genome consists of ten open reading frames (ORFs) with a 5' untranslated region (UTR) and a 3' UTR. PRRSV causes porcine reproductive and respiratory syndrome in swine. This syndrome results in failure during breeding and respiratory problems. Type 2 PRRSV was first seen in the United States in 1987. However, it has now spread worldwide to commercial swine facilities. Within the swine industry, porcine reproductive and respiratory syndrome causes interstitial pneumonia of grown swine and fetal death. Early gestation infection of a maternal swine can lead to embryonic infection. During mid-gestation, the fetuses are protected as the virus can not pass the placenta. However, in late state gestation transplacental infection to and from fetuses can occur and large scale reproductive failure may occur.

Tropism As a member of the family Arteriviridae, PRRSV has an in vivo and in vitro tropism for cells like macrophages or monocytes. PRRSV can then infect a subpopulation of macrophages. These can then be identified by the expression of sialoadhesin

Viral classification PRRSV type 2 has been historically classified according to RFLP (restriction fragment length polymorphism) patterns. These are characterized by displaying a cut pattern of three different enzymes (MluI, HincII and SacII) in the ORF5 portion of the PRRSV genome. Common RFLP types for are 1–7–4, 1–8–4, 2–5–2, among thousands of others. Criticism to this way of classifying the virus range from the multitude of possible combinations of different cut pattern of the three enzymes (leading to tens of thousands of different PRRSV RFLP patterns, with unknown epidemiological significance) to the quick change in RFLP types of a single virus in as few as 10 animal passages. Because of those limitations, PRRSV type 2 has been recently classified according to phylogenetic characteristics of the ORF5 portion of the viral genome, which aggregates isolates into phylogenetic lineages based on the ancestral relationships and genetic distance among isolates. Using this methodology, PRRSV type 2 was sub-divided into 9 lineages, which are present with different prevalence across the world. Despite type 2 PRRSV being named the North American PRRSV, there are two lineages that are restricted to Asia. The other lineages had what is assumed introductions into other geographic locations such as Thailand, Canada, China and Italy. Within the U.S., the prevalence of different lineages of PRRSV change over time. It is presumed that Type 2 PRRSV was first seen in Canada after analyzing serological evidence. By 2010, of the top ten swine production states in the United States, viruses in 3 of the 9 major lineages were present. Two of the three lineages were considered major lineages because of their sample size. By 2019, at least 5 different lineages circulate in a single U.S. region, and certain lineages display complex intra-lineage variability, which has been sometimes referred to as sub-lineages. The occurrence of specific lineages in the United States are not homogeneous, certain lineages are more prevalent in specific parts of the country. Since the 1987 classification of type 2 (North American-like) PRRSV, the virus has greatly diversified. There are three main epidemiological events that have occurred. There has been the introduction of the MN184-related cluster, acute PRRS/abortion storm, and highly pathogenic Chinese strains. The history of their incidences remain a mystery.

Genomic diversity The genetic diversity of Type 2 PRRSV continues to grow. Canada and the United States have shown the highest degree of continued diversity. In Canada, the diversity is more localized in certain areas and thought to be due to the introduction of vaccination diversity. The United States genetic diversity has increased in all geographic areas. However, Mexico contains the greatest number of genetic outliers. Researchers believe this is due to multiple reintroductions of the virus to the areas.

Vaccinations Currently, inactivated and live attenuated viruses are used to try to eliminate porcine reproductive and respiratory syndrome (PRRS). It has been found that the inactivated vaccination only induces weak neutralizing antibodies against PRRS. This type of response can create a worse infection for those who have been infected. Without a strong neutralizing vaccination, the host cells are able to attach strongly and then with weak neutralizing effects, end up getting infected easier. The live attenuated vaccine works through an unknown mechanism and only helps clinical symptoms; it does not prevent infection. It is thought that the live attenuated vaccination may also revert to the virulent form of the virus. These two vaccinations are currently not effective. There have been many new attempts to find effective vaccinations. Researchers are currently trying to identify neutralizing antibodies that will provide true immunity against type 2 PRRSV.

Structure Type 2 PRRSV is an enveloped virus with a non-isometric nucleocapsid core. The Type 2 PRRSV genome has 10 open reading frames (ORFs) present. There are two large ORFs (ORF1a and ORF1b) that encode non-structural proteins. The remaining eight ORFs create the six main structural proteins for the virus. ORF2a, 3, 4, 5, encode glycoprotein 2,2a, 3, 4, and 5. ORF2b encodes the envelope protein. There is a newly discovered protein encoded in ORF5a that overlaps ORF5. ORF6 encodes the membrane protein. The nucleocapsid (N) protein is encoded by ORF7. The N protein is composed of 123 amino acids, produces an immune response within the cell, and is thought to be multifunctional. This protein also has five antigenic regions. A cryptic nuclear localization signal (NLS), a functional nuclear localization signal (NLS-2), and a nucleolar localization signal (NoLS) are all located on this protein as well.

Genome replication cycle

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Porcine reproductive and respiratory syndrome virus 2

Start with the simplest possible case. Write down what Porcine reproductive and respiratory syndrome virus 2 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 Porcine reproductive and respiratory syndrome virus 2 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 Porcine reproductive and respiratory syndrome virus 2 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 Porcine reproductive and respiratory syndrome virus 2

In research: Porcine reproductive and respiratory syndrome virus 2 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 Porcine reproductive and respiratory syndrome virus 2 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: Porcine reproductive and respiratory syndrome virus 2 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Arteriviridae, Swine diseases, so understanding it makes those chapters shorter.
In everyday life: Look for Porcine reproductive and respiratory syndrome virus 2 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.

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How to study Porcine reproductive and respiratory syndrome virus 2 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Porcine reproductive and respiratory syndrome virus 2 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 Porcine reproductive and respiratory syndrome virus 2 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Porcine reproductive and respiratory syndrome virus 2 in simple terms?

Why does Porcine reproductive and respiratory syndrome virus 2 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 Porcine reproductive and respiratory syndrome virus 2?

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 Porcine reproductive and respiratory syndrome virus 2.