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PORCINE CIRCOVIRUS TYPE 2 ON AN INTENSIVE INDOOR PIG UNIT., Management and…

- - - - Prevention measures will reduce PCV2 incidences but not 100%. (Fernando et al., 2018)
  - - - The danger of antibiotic use is ever-growing. (Wilfred et al., 2018)
        
        Global and public health threat-antimicrobial therapy failure can occur in both humans and pigs. (Bernaerdt et al., 2022)
      - Farm workers welfare risks.
- - - - Dvorak et al. (2013) pronounced the abundance of PCV2 DNA in piglet environment or farrowing pens irrespective of sow vaccination- causing early infection of PCV2.
    - - A study illustrated that significant levels of PVC2 contamination survived in workwear and boots. PCV2 was even detected on visitors who had zero contact with the pigs in an PCV2-SI herd but was present for one hour (Neumann and Hall, 2019).
        
        Utilisation of clean gloves when handling infected specimen (Van Demark et al., 2019).
      - Use dedicated clothing when entering buildings and clean bodily fluids. (López-Lorenzo et al., 2019)
    - - All-in and all-out systems (Zeng et al., 2022).
      - Lower stocking density. (COST)(Zeng et al., 2022).
    - - A study recommended a low pressure (50 psi) rinse to remove debris then a high pressure nozzle (2400 psi) with 48.9 degrees. (Dvorak et al., 2013)
    - - A strength within disinfection is that viremia and seroconversion was not apparent after exposure to disinfected trailers. (Alarcon et al., 2013)
  - - - Cost of implementation is negligible.
    - - PCV2 cross-species transmission may be a burden to the global pig industry and beyond.
        
        Feed can be contaminated with PCV-infected swine and chicken products- source of infection for livestock.
      - PCV2 was also present in Musca domestica flies and racoon dogs. (Song et al., 2019)
        
        The PCV2-positive rates were 94.8% in infected foxes and 9.3% in healthy foxes. (Turlewicz-Podbielska et al., 2022)
      - Lack of clarity if PCV2 possesses a zoonotic potential. Some research has stated that PCV2 can infect human cells- but lacking robust scientific evidence.(Meng, 2012)
        
        Resultantly, human cells contained lower infection efficiency than within PK-15 cells- reassuring PCV infection is rare in human cells. (Díaz Cao et al., 2018)
        
        Other research has reassured that PCV2 is not deemed a zoonotic agent and will not cause detriments to human health or other livestock species.(Meng, 2012)
  - - - Positive welfare cost- euthanasia alleviates suffering for pigs. (Passler, 2022)
        
        However, compulsory euthanasia cases can hinder mental health of farmers. (Edwards-Callaway et al., 2020)
        
        Studies show that culling can hinder mental health for farmers. (Edwards-Callaway et al., 2020)
        
        Emotional costs.
      - Training is vital to ensure carcase is disposed in a environmentally appropriate, timely and ethical manner (TIME COST). (Passler, 2022)
- - - - Deemed Gold standard for confirmatory diagnosis of PCV2.(Morandi et al., 2012)
    - - Recent research stresses that clinical observations are slow and lack accuracy when developing management strategies compared to objective laboratory analysis. (Henao-Diaz et al., 2020)
        
        Thus, systemic processes like OF are reliable. (Hernandez-Garcia et al., 2017)
        
        A statistical analysis-based study illuminated that OF serves a better diagnostic tool of PCV2 DNA than faeces and serum- (p=0.001), highly significant result. (Plut et al., 2020)
        
        OF is collected more rapidly than compared to group faeces as they may not be evenly distributed, lost through slatted flooring and excrements being old.(Oliver-Ferrando et al., 2016)
        
        Direct faeces analysis- stressful, time-consuming or impractical for pigs and farmers. (COST). (Constance et al., 2021)
      - Subclinical infection costs £83.30 per pig. (COST) (Zhou et al.,2016)
  - - - Novel presentation of ropes and the enticing use of sucrose generates greater volumes of sample. More repeats increase valid and reliable results. (Dawson and Edwards, 2015)
        
        Research presents a link with rope and sucrose with reduced levels of apathy whilst increasing OF volumes if struggling to obtain samples. (Guevara et al., 2022)
        
        Engaging presentation of rope delay habituation- aligning with the freedom to express natural behaviours. Positive welfare indicator. (COST) (Almeida et al., 2020)
        
        OF- straight-forward and cheap sample collection by a single farmer, consistent with pig's everyday behaviours.
        
        Ropes encourages investigative and manipulative behaviours in pigs.
        (WELFARE COST)
        (Almeida et al., 2020)
      - However, there is a dependence on farmers to collect fresh samples in a timely manner, decant fluids into a clearly labelled container and stored in a chilled environment. (Fu et al., 2020)
        
        Fortunately, samples tend to sustain integrity but ensuring a cold chain is vital for laboratory analysis. (Decorte et al., 2013)
        
        Oral and serum fluid fails to detect persistently infected pigs with PCV2-post viremia. OF is not entirely holistic- lacking generalisability of findings to all genotypes of PCV2. (López‐Lorenzo et al., 2021)
        
        OF generates longitudinal data.
        
        Eliminates recall bias and develops cause-and-effect conclusions overtime.
        
        However, longitudinal data can be a time-consuming and expensive process. (COST). (López‐Lorenzo et al., 2021)
        
        Cleanliness is central to avoid cross-contamination of sample. (Fu et al., 2020)
        
        Interpretation of PCV2 can be complicated as it can originate from the environment. Consequently, results of OF may represent hygiene levels than the infectious status of sampled population. (López‐Lorenzo et al., 2021)
        
        A significant reduction of (p<0.005) of viral loads discovered within diagnosis- so vaccination lessens the degree of environmental contamination with PCV2. (Reiner et al.,2015)
        
        Viral detecting of OF only exists as a raw indicative method. (Decorte et al., 2013)
        
        The likelihood of PCV2 contamination of laboratory and field tissues are high. (Eddicks et al., 2022)
    - - Antibody degradation is reliant on temperature. (Trible and Rowland, 2012)
        
        However, quantitative data is sparse regarding degradation of viral nucleic acids in OF. (Ramirez et al., 2012)
        
        Incorrect fridge temperatures can cause freeze-thaw cycles of OF- potentially leading to invalid results. (Henao-Diaz et al., 2020)
  - - - Sourcing them may be expensive due to their novel nature. (Yang et al., 2017)
        
        Antiviral drugs from natural compounds like Chinese plants are deemed promising. (Chen et al., 2016)
        
        Matrine- an alkaloid compound purified and scutellarin conferred inhibition rates of 57 and 72.69%. (Sun et al., 2015)
        
        A similar study evaluating Arctigenin (ACT) rooted in a Chinese herb illustrated inhibition of PCV2 when 15.6-62.5μg/mL was administered. (Zheng et al., 2020)
        
        Attractive to public health due to natural substance- may boost revenue.
      - Real-time PCR quantifies the amount of antigen which can aid to detect other diseases like porcine respiratory disease complex. (Wang et al., 2019)
        
        PCR based assays possess greater sensitivity than immunohistochemistry assays. (Kolyvushko et al., 2019)
  - - - Novel research indicates that PCR is the most sensitive technique. (Li et al., 2018)
        
        Qualitative PCR is simply a positive or a negative result- reliable interpretation. (Trible et al., 2012)
        
        However, this diagnostic method must be used with histological lesions as a direct relationship with PCV2 process is not made. (Noh et al., 2022)
        
        PCR can effectively test routes of viral excretion.
        
        Scientists recognise PCR being optimal for early detection of viral infections. Thus, tailored biosecurity measures can be sustained early too. (Zou et al., 2023)
        
        False-positive results are still possible due to ELISA presenting differing extents of sensitivity and specificity values. (Fu et al., 2013)
- - - - Animal Welfare Costs.
      - Technically, insertion of the needle causes initial harm but the long-term protection of PCV2- initial harm outweighs this (Karuppannan and Opriessnig, 2017).
  - - - Vaccines also improve daily weight gain, feed conversion, co-infection with other viruses and uniformity during slaughter (Venegas-Vargas et al., 2021).
        
        This is paramount for determining efficacy as weaned pigs with porcine circovirus‐associated disease
        become emaciated.
  - - - Piglets require 0.5ml dose injection once by deep intramuscular injection (sows and gilts too).
        
        Less pressure on farmers as the same vaccine is used for sows and piglets. Less human errors.
        
        Sow vaccination within pregnancy reduces the blood PCV2 load and the frequency of transplacental infection (Kristensen, Hjulsager and Larsen, 2015).
        
        Some scientists have argued that vaccinating sows may obstruct the start of active immunisation in pigs at weaning (Kristensen, Hjulsager and Larsen, 2015).
        
        Sharper adaptive cellular immune response within piglets from vaccinated sows at 48-72 hours after birth. (Martelli et al., 2016)
        
        Piglet vaccination at 3 or 6 weeks induces earlier seroconversion and active immunisation which aids with PCV2 natural infection.(Martelli et al., 2016)
        
        Thus, vaccinations at 10 weeks of age is comparably less effective as viraemic pigs up to the fattening stage will not be controlled.
      - Piglets born from sows before farrowing during two consecutive gestations obtained high vitality scores than control group and controlled the number of live-born piglets at the second delivery.
        
        Vaccine immunises the sow before farrowing to heighten antibody levels during farrowing. (Jeong et al., 2015)
        
        A single-dose booster vaccination in the following gestation cycle, 2 weeks prior to farrowing ensures high antibody levels at delivery. (Jeong et al., 2015)
        
        However, scientists have argued that there are restricted research regarding efficacy of PCV2 vaccines. (Chae, 2012)
      - Gilts require 2ml injection 3 times (Heißenberger et al., 2013).
      - A study found that sow vaccination did not inhibit vertical transmission of PCV2 and virus from colostrum. But, anti-PCV2 antibodies did increase in colostrum and serum (Heißenberger et al., 2013).
        
        Scientists recognise that research into the purpose of horizontal transmission in the spread of PCV2 between farms and pigs is insufficient. (Rose et al., 2012)
    - - Sows and gilts: duration of immunity up to 5 weeks post transfer of passive antibodies through colostrum uptake.
      - Vaccination around the weaning period reduces PCV2 in serum but does not entirely eradicate infection (Venegas-Vargas et al., 2021).
        
        Enhances food conversion ratio in piglets.
    - - Single 2ml dose intramuscularly from 3 weeks of age.(Park et al., 2016)
      - Demonstrated 1,000 to 10,00- fold reduction in PCV2 viremia when contrasted with placebo group (Guo et al., 2022).
        
        Duration of immunity: 4 months. (Park et al., 2016)
        
        Contrastingly, high levels of neutralising antibodies were not generated and vertical transmission was not inhibited in a novel study (Guo et al., 2022).
  - - - One-dose vaccination of piglets reduced piglet mortality from 1.9-9.3%. (Koinig et al., 2015)
        
        Greater survivability of piglets means better piglet welfare as sow-offspring bond is sustained.
        
        As pre-weaning mortality is the predominant financial loss within the pig industry- revenue is sustained. (COST)
        
        Experimental and clinical research concluded 3.6- 10% reduction of preweaning mortality (Koinig et al., 2015).
        
        Reducing this will prevent loss of up to £23 per litter. (COST) (Stygar et al., 2022)
  - - - Polyvalent vaccines with PCV2a, PCV2b and PCV2d are lacking. Universal vaccines against all PCV2 genotypes are a future objective. (Kang et al., 2022)
      - Opriessnig et al., (2013) found cross-protection between PCV2 genotypes but porcine circovirus‐associated disease can still occur in vaccinated pigs.
- - - - 5 months immunity- 25% longer than other PCV2 vaccines on the market (Afghah et al., 2017).
        
        Approximately, £27.97 per 50 ml which is cheaper than Circovac and Ingelvac CircoFLEX (COST) (Afghah et al., 2017).
- - - - However, false positives can occur if PCR reagents or extraction are contaminated with extraneous nucleic acids. (Huang et al., 2014)