55th AASV Annual Meeting summary: Health

The 55th edition of the American Association of Swine Veterinarians (AASV) annual meeting took place in Nashville, Tennessee, also known as the Athens of the South and the Hometown of Country Music. Program director and president, Dr. Angela Baysinger, sadly passed away on Friday, March 8, after a courageous fight against stomach cancer. In her welcome message, she mentioned the importance of veterinarians in the future of swine production and the global food supply, and that we must learn from the past and steer the future. She expressed this with a quote from Albert Einstein: "Learn from yesterday, live for today, hope for tomorrow. The important thing is not to stop questioning."

Porcine reproductive and respiratory syndrome (RNA virus)

PRRSV: The never-ending story. A Maschhoff

Losses due to PRRSV are 45% in breeding sows and 55% in finishing pigs, which are currently the highest on their pig farms. The productive efficiency of sows has been increasing along with structural costs, causing profit margins not to grow. Some internal causes are high sow mortality (15.8% 2023 USA) and higher mortality in piglets and finishing pigs (4.8% US vs. 4.32% Spain). In its production system, 44.5% of the farms have suffered from PRRSV in the last twelve months. In other studies, 42% of the farms have suffered the problem. One of the causes is that the virus is worse due to its more virulent variants (L1C), plus the risk of contamination by numerous routes in production units and massive movement of pigs between sow farms and nurseries and finishers (in the USA 71% of pigs move between farms), which drastically increases the risk of contagion and the prevalence of the virus.

We need to make changes related to our role as veterinarians in both prevention measures and pig welfare, which also requires a reduction in the use of antibiotics, something not very feasible with these PRRSV cases.

Generation Z prioritizes sustainability and climate change, and we must consider this in our production vision.

Practical experiences during PRRS eradication in Hungary 2012-2022. I Szabó

PRRSV cases reduce annual production by an average of 7.4%, resulting in 1.92 fewer pigs per sow. In the USA this results in average losses of $114.71/sow and $4.67/pig. In Germany, it reached an average of 255 €/sow in a study of 21 infected farms. In a breeding sow inventory in Hungary with 170,000 heads, losses were estimated at 14.2 M$/year.

When Hungary joined the EU in 2004, 41.6% of farms were backyard farms, compared to 18.4% in 2019. More than 85% of the farms are farrow-to-finish. Most of the PRRS outbreaks are caused by European strains except for some that are caused by American strains due to the use of vaccines with such origin.

When they started the official eradication program in 2014, 4% of backyard farms and 63.9% of large-scale farms were positive. The program was completed in 2022 based on territorial principles (district, country, region) with specified time periods and was mandatory on all farms (Decree 3/2014 of 16 January). The Ministry of Agriculture created a National Eradication Committee made up of professionals, epidemiologists, and administration together with farmers, involving also the pharmaceutical companies that market vaccines. They started with a serological survey identifying the PRRS status of the farms. The category of vaccination-free farm was included.

Sera samples were tested by both ELISA and IPMA and the farms were divided into backyard, sow farms, and finishers. Of the backyard farms, 4% of the positive farms were culled at the beginning of the program. Of the sow farms, 470 farms (186,404 sows) were studied, of which 347 were negative and 27% positive, with an average size of 343 and 546 sows, respectively. A depopulation/repopulation program was carried out on the positive farms.

Regarding the origin of infection during the eradication period, 40% was from imported pigs for fattening and 50% of the times, the vehicles transporting animals for slaughter or dead animal disposal were involved. Of the pigs entering Hungary in 2014, 46% came from the Netherlands, 39% from Germany, and 12% from Slovakia. Since 2017 they decided that only PRRSV-negative animals, tested within 48 hours of arrival, could enter, which drastically reduced the entry of piglets from the Netherlands and increased those from Denmark, Czech Republic, and Slovakia. In 2022 the entire Hungarian pig population was free of PRRSV, which has led to higher profitability for the pig industry (+ 131.2 M$) going from 17.1 slaughtered pigs per sow in 2012 to 26.1 in 2022.

Communications

• The heterogeneity of field PRRSV strains leads to increased risk with the use of modified live vaccines (MLV), as transmission of vaccine virus and the reversion to virulence is possible. Other studies mention increased homologous neutralizing antibodies titers in in sows and their piglets with the use of autogenous inactivated vaccines, giving more homogeneous titers measured by fluorescent focus neutralization (FFN).
• New non-pathogenic vaccines based on the G16X strain have been shown to be safe and more immunoprophylactically effective than MLV in different farms with high prevalence.
• In postmortem samples taken from piglets (serum, tongue) environmental contaminations are detected, which can give false positives when using highly sensitive techniques.
• Iowa is the U.S. state where the most different PRRSV strains have been sequenced, followed by Minnesota, Indiana, and Illinois, and their dissemination patterns need to be better understood.
• In different studies on farms where there are numerous outbreaks, they point out that re-breaks due to PRRSV have an average duration of 213.5 days, with suspicions that the virus from the first outbreak recombined due to it evading the immune system.
• Several studies on the movement of animals in the USA show how, at a regional level, the dissemination of specific pathogens is highly associated with the movement of pigs, as in the case of the highly virulent PRRSV variants (1-4-4), with a probability of >0.99 and a coefficient of 1.872. The states that exported the most pigs were Illinois, Missouri, Oklahoma, Nebraska, and South Dakota, with the largest importers being Iowa, Minnesota, Indiana, and Kansas.
• The main secondary complications following immunosuppression due to PRRSV are Streptococcus suis and Glaesserella parasuis, leading to an increase in antibiotic use and resistance. In the USA, the most commonly used injectables in piglets are ampicillin (49%), lincomycin (31%), and enrofloxacin (20%); in finishing pigs lincomycin (72%) and enrofloxacin (28%); as well as oral neomycin (31%), sulfamethoxazole (6%), and tylvalosin (3%) in piglets and neomycin (97%) and tylvalosin (3%) in finishing pigs.

Coronavirus. Porcine epidemic diarrhea (RNA virus)

Pseudorabies virus elimination versus porcine epidemic diarrhea virus elimination: We did it before, why not do it again? L Tokach and M Potter

The USA eliminated foot and mouth disease in 1929, vesicular exanthema in 1956, classical swine fever in 1976, and Aujeszky's disease in 2004. No other pathology has been eliminated for 20 years. Perhaps it is time to consider this for the new generation of veterinarians and to reduce costs and be more competitive in net exports.

They believe the following pathologies should be considered: Mycoplasma hyopneumonia, influenza A, Seneca valley virus, PRRSV, PED, porcine delta coronavirus, and transmissible gastroenteritis virus. Perhaps the most feasible are the three Coronaviruses due to their low prevalence. For this, attention should be focused on biosecurity plans, isolation protocols, transportation, farm size, segregation processes, diagnosis, vaccines, virus survival, threats to other animals, and costs for the industry. Considering $1.00 in 1986 is equivalent to $2.73 today, they estimate the impact of the Aujeszky virus to be between $90.09-286.5/sow and for PEDV about $116.83/sow/case, which is essential to incentivize elimination.

They analyzed 466 outbreaks of PED on 302 sow farms within both the epidemic (May 1, 2013 to December 31, 2014) and endemic (January 1, 2015 to June 30, 2023) phases of the disease. The mean period that farms remained positive (TIP) was 25 weeks in the epidemic phase and 17 weeks in the endemic phase. The mean time to return to stability (TTS) was 24 and 14 weeks in the epidemic and endemic phases, respectively.

Influenza virus (RNA virus)

Experiences with influenza elimination in sow farms. J Garrido Mantilla

Influenza A virus is one of the most important pathogens in swine production, causing numerous economic losses due to its clinical presentation and predisposition to secondary infections. Vaccination is the main control measure. There is no solid virus eradication program.

An influenza virus survival program was done on 24 sow farms in Mexico. The farms were PRRSV positive and ranged from 1,800 to 4,000 sows. Each month they took 30 oropharyngeal swabs from 10 litters at weaning and analyzed them by PCR-RTr in groups of three, considering those with Cq<25 to be positive. Based on their sequencing, they chose a trivalent vaccine and performed two mass vaccinations of the entire breeding herd three weeks apart. At the same time, they stopped introducing gilts. Cross fostering was restricted to the first week of life and no nurse sows were used. Testing was done on the farms for 16 consecutive months, and 5 out of 24 were negative. On these farms, improvements in production parameters were +36.6 grams/day from weaning to slaughter, -0.45% mortality, and -0.27$/pig in treatment costs, with no significant differences in reproductive parameters. Both weaned piglets and replacement sows continue to serve as potential sources of virus reintroduction into the sow farm. It is difficult to immunize adequately with traditional hemagglutinin (HA)-based vaccines, due to the long duration of maternal antibodies.

In the USA, a neuraminidase (NA)-based vaccine has been approved for administration to piglets 3 days of age or older for the three serotypes (H1N1, H1N2, and H3N2) with DIVA capacity and promising results.

Influenza A virus: An overview of the virus, disease, and diagnostics. P Gauger. Iowa State University

Influenza A virus belongs to the Orthomyxoviridae family and has a genome consisting of six segments and between 12-13 proteins. In swine, it is a zoonotic agent and can be transmitted between humans and pigs with consequences for public health. In pigs, it usually manifests as an acute respiratory illness with high fever, lethargy, prostration, loss of appetite, abdominal breathing, and severe coughing. The virus affects both the upper and lower respiratory tract and replicates in the epithelium of the trachea, bronchi, and bronchioles. Mortality is not usually high except for secondary complications that may coexist, especially PRRSV. Some current presentations show mild symptoms or are even subclinical. Maternal passive immunity protects piglets from clinical signs, but not from infection. However, when they lose it, they can suffer the disease. The endemic forms of high prevalence in weaned piglets and the nursery phase are now frequent, where maternal immunity is quantitatively and qualitatively variable. Some more virulent strains can cause obvious clinical signs in piglets despite maternal immunity, with coughing observed when piglets are moved, knowing that not all animals are equally affected.

The history of the influenza virus in the USA began in 1918, associated with the Spanish H1N1 strain in humans. Then, the H3N2 strain was transmitted from humans to pigs in 1998. Subsequently, endemic processes have been described by circulating strains in swine: H1N1, H1N2, and H3N2 at the beginning of 2000. The pandemic H1N1 virus (pdmH1) that infected humans in 2009 had repeats that affected pigs in a reverse zoonosis process in 2010, which continued until 2023. This virus has played a role in the genetic diversity of both H1 and H3 circulating in pigs. H3 has undergone less evolution, with H1 having a greater genetic dispersion. Recently, a seasonal strain of human H3N2 has been detected in pigs in 2022 and 2023 and is not currently endemic.

The genetic diversity of the influenza virus is due to two aspects: antigenic shift and antigenic drift. Antigenic drift has fewer changes in hemagglutinin (HA) or neuraminidase (NA) genes that occur naturally during virus replication. Genetic change occurs when two viruses infect the same cell, producing a reassortment that results in major changes in the genome and the emergence of a new strain. The influenza virus has 18 HA and 11 NA surface proteins. Only the H1 and H3 subtypes are common in pigs and humans, as are the N1 and N2 subtypes. In ISU – VDL 36% of isolates are H1N1, 34% are H3N2, and 29% are H1N2 in the USA.

Influenza diagnostics and surveillance in breeding herds: New approaches and appropriate use of different sample types. D Moraes, PC Gauger, G Trevisan, G Silva, DCL Linhares. Iowa State University

Influenza virus can be endemic in breeding sows with a very low prevalence in suckling piglets (<15%). Therefore, sampling protocols are critical to understanding the epidemiological situation and the dynamics of the virus on farms. Oral fluids give us less informatio on the breeding herd contrary to these samples in PRRSV. Samples analyzed by PCR-RT are considered positive when Ct<38.

In weaned piglets, oral fluids gave a higher positive rate compared to nasal wipes. In nasal swabs and lung tissue, the positive rate was lower.

Large companies use oropharyngeal swabs on sows to detect influenza virus status and take 30 samples every two weeks from piglets in pools of five.

Limiting piglet movements is critical to reduce the spread of the virus, and it is important that nursery personnel do not go into the sow areas (also limiting the movement of people within the farm).

Mitigating the spread of influenza between pigs and workers. M Torremorell. University of Minnesota

Influenza virus transmission is bidirectional between humans and pigs. There are numerous direct (contact) and indirect (aerosols and tools) transmission routes of the influenza virus between humans and pigs. Human strains transmitted to pigs not only pose a risk to their productivity but can also be transmitted to humans in a potentiated form.

One of the main causes of the great diversity of strains in swine is transmission by people. Some studies show that 27% of workers are carriers of the virus before entering the farm compared to 41% who are positive when they leave. Samples are taken nasally. In many cases, positive workers do not show any clinical signs, indicating exposure rather than infection, but they are always documented as carriers of genetic material in their nasal cavities on a transient basis.

There are seasonal differences and the risks of introducing new strains depend on the prevalence of influenza in the population, the degree of vaccinated workers, and the types of vaccines used based on the strains circulating in humans. Thus, when consdering the transmission of the influenza virus between humans and pigs, we should not underestimate the spread of the agent. We should also reinforce biosecurity measures and limit infections in piglets before weaning since the virus has been detected on 46% of the instruments used in piglet handling and on 58% of the hands of farm workers.

African swine fever (DNA virus)

African Swine fever vaccines: Research, development, and advances. E Ramírez-Medina. Plum Island Animal Diseases Center. USDA

ASF is a lethal hemorrhagic disease caused by a virus in the Asfarviridae family with a long genome. It affects more than 50 countries in Africa, Asia, Europe, and the Pacific.

For several years they have been developing effective vaccines with live attenuated vaccines being the main candidates, using genetic manipulation of genes involved in virulence, especially in the Georgia 2007/2010 strain.

Some of these vaccine candidates were approved for use in Vietnam. Reversion to virulence has been observed in some. The center has developed three intramuscular vaccines with proven efficacy against experimental infections.

Another candidate vaccine is being developed using genetic engineering to delete a second gene (EP402R) in the prototype ASFV-G-I177L, which potentially allows differentiation between infected and vaccinated animals (DIVA). One of the major limitations in developing commercial vaccines against ASF has been the possibility of having cell lines that can support the replication of the candidate virus strain, such as the current ZMAC4 cell line, which even supports that of highly virulent strains.

New insights: Application of an African swine fever virus surrogate. S Schroeder. University of Minnesota

They studied the stability of the virus in feed, both during storage and by analyzing different inactivation processes using temperature, irradiation, or chemical decontamination as part of biosecurity programs to prevent the entry of the virus into the USA.

So far, commercial laboratories have no in vivo nor in vitro standardized testing protocols. They test procedures on DNA viruses such as the Huxley Emiliana virus (EhV - an algae virus in the Phycodnaviridae family that does not infect plants or animals) and the PRRS virus (L1A 1-4-4) because they are large viruses together with the Pretoriuskop/94/4 (Pr4) strain of the African swine fever virus. EhV and Pr4 both lose viability at temperatures above 80ºC (100ºC has a great effect without eliminating all the particles of both viruses).

EhV remains in transported feed for 23 days without losing activity. It is easily detected in soybean meal and soybean hulls.

Mycoplasma spp.

Mycoplasma elimination from regional to national level (why aren’t we there yet?) P. Yeske. Swine Vet Center

They are studying eradication programs on 721,500 sows with over 90% of the farms currently negative. Carlos Pijoan worked extensively with Mycoplasma hyopneumoniae with which he started his first control program without depopulation-repopulation.

At the end of the 1980s, after the eradication of Aujeszky's virus, genetic companies opted for farms free of numerous infectious agents, knowing they would provide better growth and lower mortality. At that time,medicated early weaning was used to control certain bacteria and in the 1990s, depopulation-repopulation programs were introduced, differentiating between disease control and elimination. Between PRRS - MYC positive vs. negative farms, there's a 170-gram difference in feed conversion, up to 5% increased mortality, and a 100-gram difference in average daily gain in addition to a 40-60% higher medication cost. They built an estimation model to assess the value of inputs used in Mycoplasma hyopneumoniae elimination programs and the resulting benefits. Acclimation programs for negative replacement sows on positive farms are a challenge if they come from PRRS - MYC negative nucleus farms. This can be a significant health instability problem.

Depopulation requires at least four weeks without pigs and six weeks without production, in addition to considering the farm's location. A minimum of 240 days is required for eradication, considering both stabilization and non-shedding time.

He recommends vaccinating future breeding gilts twice before they go into production. Elimination programs by vaccination have a lower success rate than the previous ones, not exceeding 60% in his experience. In his model, the economic benefit of elimination comes to $4.99/pig with an 86% probability of success. Obviously, biosecurity is essential to keep the disease off the farm after elimination programs.

Current trends in Mycoplasma hyopneumoniae elimination. A Sponheim

The eradication of Mycoplasma hyopneumoniae reduces the use of antibiotics, improves animal welfare and production parameters, and provides greater competitive advantages to the U.S. swine industry while making it more sustainable. Over the past 15 years, there has been an increase in programs to this effect. Farm closure and medication programs are frequently used, with the two main components being the exposure of breeding sows to the pathogen and the duration of persistence after exposure.

Aerosol dissemination of lung tissues containing the bacterium is a common practice. The expected duration of persistence is 214 days which would define the end of herd closure, based on a prevalence of <5% of PCR-positive animals. The success rate is between 64-83%.

An important point to consider is collecting samples with clean supplies to avoid false positives due to cross-contamination.

Communications

• The survival of Mycoplasma hyopneumoniae in the environment is limited, as it is easy to eliminate it through cleaning and disinfection protocols. The bacterium can survive 8 days at 4ºC in materials and environmental dust.
• New PCR-RT techniques are highly sensitive in identifying bacterial DNA in both live and dead animals and in facilities. The type of samples (oral fluids, sera, tracheal secretions) are extremely important for an accurate study.

Lawsonia intracellularis (Ileitis) Gram –

Lawsonia intracellularis is an obligate intracellular pathogen that causes proliferative enteropathy and is shed in the feces. Its presentation is mostly subclinical with economic losses centered on growth retardation, heterogeneity, and a worse conversion rate. There is still controversy surrounding the technique and the type and size of samples that should be used for diagnosis. In practical conditions, the fecal sample pool provides us with more information than oral fluids. We have increasingly sensitive specific PCRs.

They show that there is vertical transmission from dams to suckling piglets. While prevalence is low, these piglets are a potential source of infection during the post-weaning period.

Systemic PRRSV infections can affect the digestive microbiota and favor the colonization of enteric pathogens. In the early stages of finishing, an increase in the detection of both Lawsonia intracellularis and PCV2 can be observed, resulting in a greater negative impact on production indexes than if only the PRRS virus were to act.

Oral vaccination against Lawsonia intracellularis has been allowed in the USA for 20 years. They present studies on administrating it via oral gel prior to weaning with immune coverage equal to vaccination in drinking water.

combined oral vaccination against Lawsonia intracellularis and Salmonella enterica has been validated in the USA. IgA levels in oral fluids can be determined to know the immune status of the farm and evaluate the response to the vaccine.

Circovirus (DNA)

Circovirus vaccines are highly effective if properly administered. Numerous errors have been described that have caused vaccine failures and considerable wasting in both piglets and finishing pigs. Some of the most frequent are incorrect doses (half doses), inadequate storage and handling, use of inaccurate needle size, lack of cleaning of vaccination equipment, inadequate timing (age, presence of environmental stress factors - related to health or management), and animals that are left out of the vaccination program within the batches. Post-vaccination seroconversion depends on all of these factors, as well as having vaccinated in the presence of disease (PRRSV circulation), and it depends on the presence of high levels of maternal antibodies at the time of vaccination.

One study shows that blanket vaccination of breeding sows is the best immunization regimen because it further reduces viral load and increases whole-farm immunity. Ct values in fluids processed by ELISA, IFA, and virus neutralization are not correlated with the immune status of the sows.

Rotavirus (RNA)

Severe rotavirus diarrhea in young piglets is common and rarely fatal, and adult pigs are resistant due to their mature immune system. This virus belongs to the Reoviridae family and has a linear genome with 11 segments. The diagnosis to differentiate between pathogenic serotypes in piglets (A - B and C) can be performed by new molecular qPCR-RT techniques.

Streptococcus suis (Gram +)

Streptococcus suis resides asymptomatically in the pig's gastrointestinal, reproductive, and respiratory tracts, but if it crosses the epithelial or mucosal barrier it causes infections in other areas of the lymphatic system leading to arthritis and sepsis, such as meningitis when it crosses the blood-brain barrier.

Early colonization in piglets occurs at birth even though the clinical signs are usually observed starting at four weeks of life, with genetic similarity found between the strains isolated in the vaginal mucosa of sows and the respiratory tract of piglets.

S. suis bacteria mainly affect weaned piglets as a primary or secondary agent, causing systemic infections. Changes in its virulence and variable responses to antibiotics are described due to the considerable inflammatory response it produces. The immune system tries to compensate for these alterations by modulating the pro-inflammatory and pro-oxidative responses to minimize tissue damage.

We can carry out nutritional actions to modulate this inflammatory response. In a study with eight field trials, they tested reducing ileal digestible lysine levels by 20%, obtaining a 1% reduction in mortality and a 14% reduction in antimicrobial costs. Logically, piglet growth is also reduced. They conclude that the connection between rapid growth in lean tissue deposition and its effect on increased susceptibility to pathogens is not entirely clear and requires further research on protein synthesis and increased susceptibility to Streptococcus suis. They do not consider that this can be extended to other pathogens.

It is considered a zoonotic pathogen since it can cause disease in humans and pigs. Numerous cases of meningitis have been described in people in Asia who have consumed uncooked pork products. Autogenous vaccines are used with not very encouraging results due to the diversity of their serotypes and the absence of cross-immunity. Some Bacillus spp strains such as 839 and 1999 can inhibit certain pathogens, having antioxidant properties and immunomodulatory effects.

The main antibiotic resistance genes in Streptococcus suis are tetO (89%) and ermB (80%). Ninety-seven percent of the isolates were resistant to tetracycline and were highly sensitive to ampicillin, ceftiofur, penicillin, florfenicol, and enrofloxacin with resistance ranges between 0-7.8%. They do not detect genes resistant to beta-lactams.

Salmonella

Salmonella infection in swine can be subclinical depending on the serotype of the bacterium. The most prevalent in the USA is Salmonella enterica serovar 1. Feces are reference samples with the option to analyze by qPCR although results do not give us an accurate idea of the animal's clinical status or their shedding status. Specific culture media are very sensitive to identify the bacteria.

Escherichia coli

During testing over the past twelve years (3,240 isolates), the University of Iowa Veterinary Diagnostic Laboratory has determined that the most frequent E. coli ETEC fimbriae gene isolates are F4(K88) and F18 with 30% and 68% respectively, with antibiotic sensitivities having changed during this period. Since 2019 they have observed an increase in F18 fimbria. Enrofloxacin-susceptible isolates have been drastically reduced with no variation in ceftiofur sensitivity. Since 2017 they have found lower sensitivity to florfenicol, gentamicin, neomycin, sulfadimethoxine + trimethoprim. Cases due to E. coli are much higher than the average from previous years, identifying the tia gene as a potential virulence factor contributing to post-weaning diarrhea. A better understanding of its pathogenesis is needed.

E. coli strains that cause post-weaning diarrhea are enterotoxigenic, characterized by the expression of fimbriae and enterotoxins. E. coli is part of the intestinal microbiome, with certain strains known to possess virulence genes that contribute to disease development. In addition to F4 and F18 fimbriae, F5 (K99), F6 (987P), and F41 have been identified in post-weaning diarrhea. They are responsible for producing hypersecretory diarrhea derived from thermolabile (LT) and thermostable (Sta, Stb, and EAST) enterotoxins that induce an increase in water and electrolyte secretion into the intestinal lumen while inhibiting their absorption with consequent dehydration and acidosis. The prevalence of the different ETEC virotypes varies between regions and timeframe.

Antonio Palomo Yagüe