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Bacterial pathologies
Ileitis – Oral fluids are convenient because of their ease of collection, reduced diagnostic costs, and the fact that other pathogens can be detected. For Lawsonia intracellularis infections, which colonize the intestinal mucosa and are excreted in the feces rather than the saliva, a large sample size increases the detection potential. Collecting oral fluids in pens is an excellent alternative to fecal samples to detect subclinical infections of Lawsonia intracellularis, demonstrating different sensitivity by PCR. In farms with subclinical cases, fecal samples have good sensitivity, whereas in farms with differential symptoms the pattern is the opposite due to the different levels of excretion. Using the vaccine leads to improvements in the feed conversion ratio which, using the TEKLa calculator, results in a 6.23% reduction in CO2 emissions along with a 5.4-5.9% reduction in nitrogen excretion according to German studies. There are numerous studies on the advantages of vaccination in improving production parameters (average daily gain, conversion rate, and homogeneity of pigs at slaughter), as well as in the lower prevalence of enterotoxemia by Clostridium spp and Salmonella, reducing clinical symptoms, as reported in a study on co-infections with Brachispiras spp.
Swine dysentery – Brachyspira hyodysenteriae remains a problem on farms in much of the world. The achivement of active inmunity through vaccination is not fully acomplished and control is focused on metaphylactic practices with antibiotics and feed additives (phytobiotics, essential oils, and prebiotics) whose exact mechanism of action is not well understood. In this pathogen, the flagellum is the main virulence factor as it is responsible for its mechanisms of chemotaxis, adhesion, and invasion of intestinal mucosal surfaces. Inhibition of its hemolytic activity can be selective to reduce the pathogenic effect of the bacterium. As it is a Gram-negative anaerobe, we can focus its control with additives in this sense and take into account its high persistence in soil, rodents, and slurry.
Streptococcus suis
• Some strains of S. suis can express virulence genes that enable the bacterium to cross the blood-brain barrier and access the central nervous system and are zoonotic, as we know. They performed an antibiotic sensitivity test on isolates in the USA over 10 years (1,020 isolates in the nervous system) and found that MIC50 and MIC90 were stable for ampicillin, ceftiofur, chlortetracycline, clindamycin, enrofloxacin, florfenicol, neomycin, oxytetracycline, penicillin, spectinomycin, tilmicosin, tulathromycin, and tylosin.
• A sensitive and specific qPCR based on an associated virulence marker (VM1) has been validated. It is used as a test on antemortem samples for longitudinal studies of disease dynamics associated with Streptococcus suis in lactating sows and their piglets during lactation and weaning. Prevalence is usually higher in the first and last week of lactation and is higher in gilts than multiparous sows.
• A study conducted in Spain from 2019 to 2023 characterizing 250 Streptococcus suis isolates in piglets at weaning determined that 43.6% have the cps1 gene, with 89.9% identified as serotype 1 and only 10.1% as serotype 14. In isolates with the cps2,1/2J gene, 56.4% were found, of which 69.5% are serotype 2 and 30.5% are serotype ½. None of the isolates presented less than two virulence factors and 35.6% were positive for all genes tested. As for virulence-related serotypes, serotype 1 was in 88.8% of the 4 or 5 virulence factors studied, compared to serotype 2 (78.6%), serotype 14 (72.7%), and serotype ½ (72.1%). Serotypes 1 and 2 are the most common in Europe, together with serotype 9.
• One of the main virulence factors of S. suis is a capsular polysaccharide (CPS) with limited immunogenic capacity in the use of vaccines. However, if conjugated to a protein carrier, glycoconjugated vaccines can be produced as is done for humans, which is costly. New technological advances make it possible to make carbohydrate-based vaccines. In trials with pigs, antibody production is variable and more studies are needed. The use of autogenous vaccines gives varied results, it is thought there is possible interference of maternal antibodies, although it has not been tested yet. In some studies vaccinating piglets at 3 and 5 weeks old such interference is scarce.
• Numerous studies have been presented in which the use of certain feed or water additives affects its prevalence and severity, giving very variable results.
Mycoplasma hyopneumoniae
• Indirect transmission routes have been little studied, assuming that the agent lives only a short time in the environment. Different studies using contaminated materials, water, or feed determined that the bacteria were not found after four days, and pigs exposed to those materials previously contaminated by aerosol did not develop the infection or disease. The risk of transmission via fomites is minimal.
• Cross-contaminations in samples sent to the laboratory are frequent, leading to diagnostic errors. It is important to take samples under hygienic conditions (protocol and materials) to avoid incorrect interpretations. Hydrogen peroxide is a good product for cleaning sampling materials. The possibility of reinfection in sows is very high under practical conditions.
Mycoplasma hyorhinis – This bacterium is known to be responsible for polyserositis and polyarthritis in weaned piglets, although in recent years it has been isolated in cerebrospinal fluid and meningeal swabs from piglets with nervous symptomatology and histological lesions in the brain (fibrionopurulent meningitis) and spinal cord (central nervous system) in different countries. Differential diagnosis with Streptococcus suis and Glaesserella parasuis should always be made.
Actinobacillus pleuropneumoniae
• Swine pleuropneumonia is found globally, with the serotypes responsible for acute and chronic disease varying by country in relation to their virulence. Diagnosis by serology, special paper cards (ANICARDS), and lung samples for PCR analysis are the three most commonly used techniques, giving different percentages of positivity. Keep in mind that samples not immediately refrigerated can become contaminated, leading to questionable results. High temperatures also affect the survival of the bacteria in water and feces, and it is best to keep them at temperatures above 4ºC.
• Lesions in dorso-caudal pulmonary lobes and pleuritis are characteristic of chronic pleuropneumonia, and should be differentiated from cranioventral consolidations due to Mycoplasma hyopneumoniae.
• The most common serotype in the USA is 15, which is not associated with high mortality. The use of different vaccines shows encouraging data.
General
• Disease prevention and control within the One Health concept is important to reduce antibiotic use and antimicrobial resistance. ROADMAP is a multidisciplinary European project carried out in Belgium where 19 farms are included voluntarily for 18 months. During visits, they identify cleaning and disinfection systems, colostrum collection, or both. They analyze the cleaning and disinfection processes by taking samples at the farm level and estimate the number of colonies per plate with an index of 1 to 5. To analyze the colostrum collection, they do ELISA against PCV2 to know if it has been sufficient or insufficient. Four genetic lines are involved (5 Danbred, 10 Topigs TN70, 1 Hypor, and 3 local genetic lines), with 1, 3, and 4-week batch management. The results of the presence of antimicrobial resistances at the beginning and end of the study were reduced. The use of foaming detergents for cleaning/disinfection and actions in water sanitation were positive measures. In terms of colostrum intake, the litter size, the size of the piglets especially, the cross-fostering systems, as well as moving piglets ahead influenced the intake of sufficient colostrum.
• They presented a Spanish project, PigMarkSal, (University of Murcia, UaB, Cefusa, Acuvet, and ADA) that aims at analyzing the state of sanitary control, monitoring salivary inflammation and oxidation markers, where cytokines and inflammatory cells (neutrophils) are produced. Oxidative damage occurs when the oxidant/antioxidant balance is disrupted and cells, tissues, and organs are affected. Biomarkers of the inflammatory response are myeloid lineage cells. Neutrophil activation expresses proinflammatory proteins and secretion of proinflammatory cytokines. S100A12 can regulate this process and can be detected in saliva, where it is found in elevated levels in numerous pathologies in finishing pigs. Salivary biomarkers of oxidative stress are analyzed from total antioxidant capacity, total oxidative status, and oxidative status index (oxidant/antioxidant ratios). The kinetic response is not well known, having different magnitudes, which requires controlling the test conditions to determine its sensitivity. In a trial, they used 13 male finishing pigs with respiratory symptoms and took saliva samples to analyze their oxidative status at days 0, 1, 2, 4, 7, and 15 after antibiotic treatment. They found a correlation between inflammation and oxidative markers, which were reduced during antibiotic treatment, with statistical significance. They concluded that inflammation and oxidation in pigs can be evaluated using salivary biomarkers S100A12 y TOS (pigmarksal.com).
• In a study carried out in Brazil with ISU, the cost of using intramuscular and intradermal vaccines was analyzed using a cost-minimized analysis (CMA) based on three types of vaccines with the same efficiency and benefits. An Excel model was constructed based on a large company with 38,000 sows, with Mycoplasma hyopneumoniae and porcine circovirus vaccines. They analyzed the cost of vaccine storage for 30 days (electricity and depreciation of refrigerators for 4 years), vaccination equipment (25 injections per needle and 16,500 injections per needle), maintenance, vaccination time, cost of waste (vials, needles, packaging), and cost of seizures due to abscesses in IM which was reduced by 65% in ID (-25 g/ IM carcass). The differential annual cost for the 38,000 sows was $65,776/year ($1.73/sow/year or $0.06/pig to slaughter) to which we must add the safety for the workers who administer them, less working time, worker retention, accident costs, and medical insurance, added to food safety due to needle breakage and environmental impact and carbon footprint. We must also take into account improved pig welfare and lower risk of iatrogenic transmission.
• The cross-fostering system is based on having more piglets than functional teats, which has increased in recent years. It is 100% in the Netherlands, moving up to 27% of piglets between batches and 49% cross-fostering after day four. Small piglets are usually placed with first parity sows. The expected results are to wean more piglets, with the understanding that it causes stress and increases the risk of spreading diseases. They conducted a trial on a farm with 860 TN70 sows identifying piglets individually at birth with the LeeO system before cross-fostering. They classified the piglets by weight: >1.48 kg, 1.06-1.48, and less than 1.06 kg at birth, as well as when cross-fostering occurred: 0-3, 4-7, and 8 days or more. They calculated the average daily gain and mortality throughout the entire life of the pigs. More than three changes increased mortality, with it being higher in the group of smaller piglets (30% vs. 6% and 9% between small, large, and medium piglets). Logically, the largest piglets maintained the same mortality (6%) regardless of the number of movements (0 or 3), while the medium-sized piglets had increased mortality with the number of changes. The average daily gain was logically higher in the larger piglets, followed by the medium and small ones. If cross-fostering is done after 8 days of life, the average daily gain is reduced, with higher mortality when cross-fostering is done between 4-7 days of life. They conclude that it is important to limit cross-fostering and do it only at an early age after colostrum intake and to move only the larger piglets at an early age if we base it on the best welfare and better productivity.
• The prevalence of Klebsiella pneumoniae as a cause of septicemia, especially in the summer months, was first diagnosed in England in 2011. It causes sudden deaths (5-16%) due to its highly virulent Kpp ST25 strain in piglets from 9 days old to weaning.
• Pasteurella multocida type A causes moderate to severe pneumonia in pigs, with both acute and chronic cases and with multifocal lesions of suppurative bronchopneumonia with abscesses and fibrinous pleuritis, as well as pericarditis and septicemia. Six virulence genes were found present in all isolates (ompA, ompH, oma 87, exbB, exbD, and ptfA).
• Escherichia coli ETEC is responsible for preweaning and post-weaning diarrhea in piglets. From what we know from humans, the gene tia is considered a virulence factor contributing to post-weaning diarrhea, and further research on its pathogenesis is needed.
• Clostridium perfringens is a relevant bacterium in neonatal piglet diarrhea, with the STs toxins (2, 21, 39, 179, 583, and 772) being the most relevant. In several studies done in China on the etiology of diarrhea in piglets less than 14 days old, it was determined that 63% of the farms isolated Escherichia coli with a higher prevalence of F4 and LT toxin. Clostridium perfringens type A was found in 100% of the farms and 59% were positive for Rotavirus A, 29% for Rotavirus C, and 18% for porcine epidemic diarrhea virus. Only 18% of the farms were positive for both rotaviruses, knowing that 81% of the farms were positive for three or more of the detected agents. Numerous studies refer to the different isolates of rotavirus, their prevalence, and severity between farms and countries, highlighting the lack of sensitivity of some techniques that vary with different rotaviruses (in Spain with C). The use of vaccines is showing positive results; keep the different co-infections in mind when considering their level of efficacy and profitability of use.
• Piglets' fecal microbiota varies before and after weaning, with it being different between days 1 and 3 then tending to homogenize between days 7 and 21 after weaning.
• Staphylococcus hyicus is a normal skin commensal in pigs but can cause serious exudative dermatitis problems. Its treatment with antibiotics gives mixed results due to the development of antimicrobial resistance.
• Streptococcus dysgalactiae is a relevant pathogen that causes polyarthritis in piglets.
• Since 1980, oral fluids have been used for research on human immunodeficiency virus as well as other pathogens. In major US laboratories, 1,650,000 analyses of oral fluid samples were performed between 2019 and 2022. The original dilemma arose in 2012 when analyzing antibodies by ELISA from oral fluids, centered on the dilution used. Oral fluids for early detection of classical swine fever at the commercial level were described in 2023 and for African swine fever in dead animals in 2021. This study's objective was to compare and quantify the transfer of pathogens from the environment to the animals based on oral fluids. They used two tracers such as tetracycline and rhodamine B. They took three commercial wean-to-finish farms, with groups of 30, 60, and 125 pigs, putting the pigs in one group in contact with individual animals and the other group in contact with the medium, with a contact time of 30, 60, or 90 minutes. The behavior of the pigs with the ropes was erratic, estimating that the contact was 40%, 23%, and 10% in the groups of 30, 60, and 125 pigs respectively. They conclude that oral fluids are good samples for detecting enteric pathogens (PED, TGE, PIA).
Immunology and vaccinology
The porcine host and immunological escape. D. Werling. University of London
Swine pathogens (bacteria, parasites, and viruses) have a wide variety of both innate and adaptive mechanisms inducing the production of inflammatory, autophagic, and apoptotic cells to evade the host immune response. Persistent infections often impede the effective development of vaccines, which imposes certain technical barriers. We do not have a complete understanding of virulence-related genes, the main pathogenesis genes, or the mechanisms of immunoregulation. During intrauterine development, the blood supply from the mother to the embryos/fetuses via the placenta is separated by six layers, making it difficult for maternal cells and immunoglobulins to pass through. Innate immunity at birth is realized by two mechanisms: the recruitment and activation of cellular components such as macrophages, neutrophils, natural killer (NK) cells, and dendritic cells, as well as the release of a broad spectrum of extracellular mediators such as cytokines, chemokines, complement, and antimicrobial peptides. Cellular components of the innate immune system, such as polymorphonuclear leukocytes, macrophages, and dendritic cells, appear together with the hematopoietic activity of the first lymphoid organs. At the same time, NK cells can be isolated at day 45 of gestation from umbilical cord blood and the spleen. T cells in neonatal piglets may account for up to 50% of peripheral white blood cells, which are involved in the innate immune response, able not only to modulate the immune response at the mucosal level but also to present the antigen to other immune cells.
The lymphatic system of growing embryos is physically formed by day 35 of gestation, with lymphocytes beginning to function around day 45 of gestation, with a limited and non-specific antibody repertoire capacity in the last third of gestation (natural antibody repertoire) that can confer some protection to the newborn piglet. Neonates do not have a fully competent adaptive immune system but they are born with fully functional innate immune cells and extracellular components to respond to infections affecting mucosal surfaces. This is enhanced by colostrum intake, which contains maternal antibodies and immunomodulators in addition to immune cells from the sow. Regardless of environmental situations, the pool of B and T cells in response to antigens develops from birth, and constantly increases in correlation with the diversity of antigens they recognize before weaning. The first microbiome that the piglet acquires from its mother at birth develops both immune and adaptive responses, in addition to postulating itself in the mucosal immune system from the moment it comes into contact with external antigens. The development of the microbiome-immune system complex (digestive-immune system axis) guides the animal's immunocompetence, creating piglets that are tolerant to both feed and commensal bacteria. If we do not have a correct microbiome, it facilitates the establishment of pathogenic agents, as shown in the cases of Mycolplasma hyopneumoniae and Lawsonia intracellularis.
Pathogen strategies of immune evasion. T. Vahlenkamp. Leipzig University
As farms become more intensive, the impact of infectious processes generally becomes more severe. Viral processes range from subclinical to clinical forms, e.g. influenza virus and rotaviruses. Intracellular pathogens are exposed to the defense mechanisms of infected cells, so for virus evolution, it is important to protect their genetic information (DNA, RNA) from intracellular nuclease activity. To initiate their replication in the cell, the viral genome is packaged in the center of the structural proteins. After infection, nonstructural proteins encoded by the viral genome are the first to express such proteins, responsible in the first instance for evading the immune response. In the best-case scenario, the innate immune system can inhibit the first steps of virus replication, making it more normal for the virus to enter the cell and gain access to its genetic material, amino acids, and cellular-based machinery that is required to generate its virus progeny. RNA viruses can discern the different modifications, whereas DNA viruses can be localized within the cell. The first step in the host's innate immune response is the production of interferon I, II, and III, as well as proinflammatory cytokines and chemokines. Some of the viruses that interfere with the mechanisms of this innate immune response are Aujeszky's virus, porcine circovirus, porcine epidemic diarrhea virus, porcine reproductive and respiratory virus, porcine deltacoronavirus, African swine fever virus, and influenza virus. PRRSV induces an alteration of immunoregulatory cytokines, which causes a prolonged delay in the activation of cytotoxic lymphocytes (CTL) and production of neutralizing antibodies, causing severe disorders of the immune response by the pig, prolonging viremia, transiently decreasing the production of immune T cells and delaying the protective response by antibodies.
• Novel vaccines are being developed from a yeast-based platform to address the major drawbacks of subunit vaccines. They focus on a series of recombinant Kluyveromyces lactis strains using recombinant methods. These strains can integrate multiple expression proteins, giving rise to numerous antigenic proteins in a single eukaryotic cell.
• The prophylactic and metaphylactic use of antibiotics is not prohibited in Brazil, and they are used in conjunction with certain vaccines. Several antibiotics used at the time of vaccination against Lawsonia intracellularis negatively interfere with the generation of IgG, reaching a reduction of up to 41.15% in some (ceftiofur, doxycycline, tulathromycin), with no adverse effects found with amoxicillin, florfenicol, tiamulin, and tilpiridosine.
• Colostrum provides newborn piglets with energy and IgG. Levels of 26-28 g/L of IgG at 24 hours after birth are considered sufficient for their immunity. These levels are considered indirectly by Brix refractometry. They find a direct correlation between the Brix data and the IgG concentration (y = 0.1503x + 15.171).
Health management
• Can vehicles transmit animal diseases that affect production?
The transmission of infectious agents is dynamic. Studies are being conducted at the University of North Carolina based on the vertical flow of animals moving via transport. Vehicle movements create uniform connections between farms, which is a cause for concern. Transports of live animals, feed, and people must be disinfected between farms, and cleaning and disinfection measures are poorly understood in terms of their efficiency in preventing transmission. Some studies aim to assess the advantages and disadvantages of such dynamic movement of vehicles on 2,000 farms, 654 vehicles, 14 cleaning stations, 8 feed mills, and 9 slaughterhouses. They carry out different simulations with vehicle routes between farms, from farms to feed mills to farms, and from farms to slaughterhouses. The rerouting strategy reduces the number of contacts between points of contagion, with the disadvantage of increased costs. https://doi.org/10.17605/OSF.IO/576QB
• The European consortium project BETTER (CA20103) investigates how biosecurity measures are applied in production systems in Europe and considers infectious diseases according to their different transmission routes, internal and external biosecurity measures, the heterogeneity of European pig production, and the legal regulations in force in intensive production in times of stability. They developed a questionnaire with 51 biosecurity measures (19 internal and 32 external) with positive or negative answers, both from legislation and from the industry. The questionnaire was sent to 38 countries. Of the legal biosecurity measures, Spain, France, Italy, and Romania have the fewest measures in place compared to Ukraine (specific legislation against ASF), followed by Ireland, Estonia, Finland, Switzerland, Slovenia, Sweden, Greece, the Netherlands, Serbia, Belgium, Denmark… They establish this number of legal measures based on the size of pig production as well as between EU and non-EU states. The results regarding biosecurity measures include 21.1% and 40.6% (internal and external respectively). The ten most frequent measures in national legislation are not feeding pigs swill, transport documentation, fencing of farms, entry to farms with specific hygiene measures (clothing, boots), criteria for insemination centers, and rodent control as external measures, with internal measures being vaccination programs, with specific health programs by veterinary services. The least common measures are sanitary downtimes and the time between farm visits. Measures applied by the industry, apart from the legal ones, are implemented differently by countries regardless of their pig production and status within or outside the EU. https://better-biosecurity.eu/.
• Antimicrobial resistance to methicillin in Staphylococcus aureus (MRSA) is a major health problem. In Austria, it has been shown that diphtheria flies can be vectors for transmission of this resistance on pig farms, both to pigs and to people and other animals.
• The inclusion of antibiotics in sow feed is not associated with a lower incidence of neonatal diarrhea, with the risk factors being sow parity and piglet age.
• The transport of live pigs with poor biosecurity measures, in addition to being a source of dissemination of infectious agents between farms, also contributes to the spread of antimicrobial resistance.
• The direct transmission of antibiotic resistance from farm to table is highlighted in the case of beta-lactams. Fresh meats have a higher risk of transmission than processed and cured products. The prudent use of antibiotics on farms, the correct management of food production at different stages, and the environment continue to play a strategic role in the dissemination of antimicrobial resistance.
• Cleaning and disinfection measures in farm environments are gaining importance within biosecurity measures to minimize the transmission of pathogens from one group of animals to another, helping reduce the selective pressure of microorganisms and their persistence in the environment. Many of the bacteria found when cleaning and disinfection measures are not sufficient (Staphilococcus spp – sciuri, saprophyticus, xylosus, cohinii, equorum, epidermidis, and haemoliticus) are considered reservoirs of antibiotic resistance genes, both in animal and human pathogens, capable of causing nosocomial infections. After strict cleaning and disinfection, an Italian group reports a 20% reduction in antimicrobial resistance.
• The etiology of hemorrhagic bowel syndrome (HBS) is not well defined, and intestinal torsions are found especially in the colon and mesentery. The higher prevalence in autumn and the use of raw materials from the harvest, together with temperature fluctuations, have been shown to be correlated, and no association has been found with farms with clinical symptoms of ileitis due to Lawsonia intracellularis.
Antonio Palomo Yagüe
