Porcine enzootic pneumonia

PRESENTATION

BROCHURE

PORCINE ENZOOTIC PNEUMONIA Beatriz García-Morante, Joaquim Segalés and Marina Sibila

Porcine Enzootic Pneumonia

PORCINE ENZOOTIC PNEUMONIA Beatriz García-Morante, Joaquim Segalés and Marina Sibila

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AUTHORS: Beatriz García-Morante, Joaquim Segalés,

Marina Sibila.

FORMAT: 11 × 20 cm.

NUMBER OF PAGES: 96.

NUMBER OF FIGURES: 25.

BINDING: paperback, wire-o.

RETAIL PRICE

€35

Porcine enzootic pneumonia is a chronic respiratory disease caused

by Mycoplasma hyopneumoniae, producing high morbidity rates and great economic losses. This handbook attempts to update, condense and simplify the large amount of available information about porcine enzootic pneumonia, including a high number of graphic contents to provide the veterinary surgeon with a handy tool to fully understand, treat, control and prevent this disease.

Tsekhmister/shutterstock.com

Porcine Enzootic Pneumonia

Presentation of the book The importance of Mycoplasma hyopneumoniae infection in pig production has been known for some decades now. Despite the long journey taken to develop an understanding of the pathogen and its main clinical presentation, enzootic pneumonia, there are still some important questions to answer. This book updates the reader with the latest advances in understanding the nature of the infection caused by this pathogen, from the known variability of M. hyopneumoniae and its potential clinical implications, to new trends in diagnosis, management and even eradication.

The book also attempts to bring the knowledge generated in the academic and research spheres to the professionals who work in the field and have to deal with this infection and its consequences every day. We wanted to create a practical handbook which would be help resolve any doubts about M. hyopneumoniae and its associated diseases. It is also aimed at veterinary students with a particular interest in pigs, as it can undoubtedly give them a better understanding of one of the most important pig diseases worldwide. The book also aims to link the academic world with farming practice, and to portray both perspectives. It has been designed to be very visual and highly practical, with the use of tables, diagrams and images throughout the work. We, as authors, have taken a pedagogical approach in dealing with some very complex concepts, and have undertaken to provide the reader with a broad understanding of the many different aspects of the disease.

Beatriz GarcĂ­a-Morante, Joaquim SegalĂŠs and Marina Sibila.

The authors Beatriz García-Morante

hkeita/shutterstock.com

Beatriz García-Morante graduated from the Autonomous University of Barcelona (UAB) with a degree in veterinary medicine in 2012, and gained an interuniversity Master’s Degree in Advanced Immunology from the UAB and the University of Barcelona (UB) in 2013. She earned her PhD under the Government of Catalonia’s Industrial Doctorates Plan in 2017, in a collaborative arrangement between the pharmaceutical industry and CReSA (Centre de Recerca en Sanitat Animal; Centre for Animal Health Research) at IRTA (Institut de Recerca i Tecnologia Agroalimentaries; Institute of Agri-Food Research and Technology), located on the UAB campus. Her doctoral thesis sought improvements to the experimental model for the study of Mycoplasma hyopneumoniae infection, under the supervision of Dr Marina Sibila and Dr Joaquim Segalés. She has published articles in national and international journals, and has also been a resident of the European College of Porcine Health and Management (ECPHM) since 2015, mentored by Dr Sergio López and Dr Joaquim Segalés.

Porcine Enzootic Pneumonia

Joaquim Segalés Joaquim Segalés graduated in veterinary medicine from the UAB in 1991 and was awarded his PhD by the same university in 1996, after spending 15 months at the University of Minnesota (UM) in the USA, codirected by Dr Mariano Domingo (UAB) and Dr Carlos Pijoan (UM). He became a diplomate of the European College of Veterinary Pathologists (ECVP) in 2000 and by the ECPHM in 2004. He is a founding member of the ECPHM and was its president between 2013 and 2016. Dr Segalés is a tenured lecturer at the Department of Animal Health and Anatomy of the Faculty of Veterinary Medicine at the UAB, and he is also a researcher with CReSA–IRTA, where he was director between 2012 and 2017.

He participates in many Spanish and European research projects, and collaborates with Spanish and international companies in the pig production sector. His research includes porcine respiratory and reproductive syndrome virus (PRRSV), Haemophilus parasuis, Aujeszky’s disease virus (ADV), Mycoplasma hyopneumoniae, hepatitis E virus, torque teno sus virus (TTSuV), and diseases associated with porcine circovirus type 2 (PCV2). He is coauthor of over 270 articles in international scientific journals, 10 chapters of internationally acclaimed books, a book on pig necropsy, and 3 books on clinical cases in pigs.

Marina Sibila Marina Sibila graduated in biological sciences from the UB in 1999. Under the supervision of Dr Maria Calsamiglia, she completed her PhD on the molecular epidemiology of M. hyopneumoniae infection at the Faculty of Veterinary Medicine of the UAB in 2004. She is currently a researcher at CReSA-IRTA, where she is continuing her work on M. hyopneumoniae and other pig pathogens, including PCV2, PRRSV, Haemophilus parasuis, Actinobacillus pleuropneumoniae, Mycoplasma hyorhinis, and TTSuV. Her research includes molecular epidemiology, the development of experimental models and diagnostic tools, and vaccine efficacy studies. Dr Sibila collaborates in many Spanish and international research projects, and she has published more than 60 scientific and educational articles. She is also co-author of a book chapter on the evaluation of lung lesions in pigs at the abattoir and a handbook of laboratory diagnosis in pigs. Dr Sibila has participated as a speaker at various conferences in the sector, both in Spain and internationally, and her teaching activities have included PhD courses and classes for a master’s degree in swine health and production and directing various doctoral theses

PORCINE ENZOOTIC PNEUMONIA Beatriz García-Morante, Joaquim Segalés and Marina Sibila

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Table of contents 1. Mycoplasma hyopneumoniae, primary agent Some history...

Characteristics of mycoplasmas Culture and isolation Pathogenesis of M. hyopneumoniae infection Disorders associated with M. hyopneumoniae infection

2. What are the clinical signs of M. hyopneumoniae infection?

Clinical diagnosis Pathological diagnosis Macroscopic lung lesions Microscopic lung lesions

Laboratory diagnosis Detecting the pathogen Detecting the antigen Detecting genetic material Detecting specific antibodies

Sampling Suspicion of an epidemic form Monitoring M. hyopneumoniae infection status on a farm (endemic form) Monitoring to confirm negative status

3. How and when is M. hyopneumoniae transmitted?

Biosecurity Duration of the lactation period Fostering

Distribution and prevalence

Antimicrobial therapy

M. hyopneumoniae: mode an timimg of transmission

Vaccination

Dynamics of M. hyopneumoniae infection

4. What do we know about M. hyopneumoniae strains?

Diversity of M. hyopneumoniae Variability from country to country or region to region Variability on an individual farm Variability between pigs

How is the clinical situation affected by the strain diversity?

Effect of variability on vaccine efficacy Effect of variability on antibiotic efficacy Effect of variability on sensitivity of diagnostic techniques

5. What happens after infection?

Disease risk factors Management, housing and biosecurity Production system Gilt acclimatisation Stocking density

6. Is eradication possible?

Justification for eradication programmes Eradication programmes Confirmation of successful eradication

7. What have you learnt about the disease?

Quiz Self-assessment

8. References

2 What are the clinical signs of M. hyopneumoniae infection?

PORCINE ENZOOTIC PNEUMONIA

CLINICAL DIAGNOSIS

Table 1. Summary of the clinical characteristics of endemic and

epidemic EP.

Coughing and dyspnoea are the main clinical signs of respiratory diseases. They can be caused by a wide variety of infectious agents, and modified by coinfections and environmental factors.

Their aetiology is quite unspecific. A dry, nonproductive cough in fattening pigs is a clinical sign that is consistent with the diseases associated with M. hyopneumoniae.

A nonproductive dry cough is suggestive of, but not exclusive to, M. hyopneumoniae infection.

Under experimental conditions, coughing tends to start 2 weeks postinfection (p.i.), although this incubation period can vary from 1 to 3 weeks. However, this period can vary considerably in the field, and can be as long as 6 weeks. Coughing can last between 1 week and 2 months under both experimental and farm conditions. It is important to remember that subclinical M. hyopneumoniae infections are common and are not linked to any obvious clinical signs.

A noncomplicated M. hyopneumoniae infection causes a nonproductive dry cough of chronic nature and mainly affects fatteners. The disease is characterised by high morbidity, low mortality and has a limited effect on the animal’s productive performance.

Endemic EP Incidence Type

Epidemic EP

High

Low

Chronic

Acute

Morbidity

High

Very high

Mortality

Very low

Medium–low

Where?

Herds that are immunologically positive for M. hyopneumoniae, whether through vaccination or continual field exposure.

Herds that are immunologically negative for M. hyopneumoniae.

Introduction of M. hyopneumoniae into farms previously free of the disease and unvaccinated.

Animals over 6 weeks of age, especially during the fattening stage.

Animals of all ages, but usually during fattening.

Who?

Subclinical presentation, or nonproductive dry cough with a gradual onset. Other Clinical signs more severe signs tend to be the result of concomitant infections.

Nonproductive dry cough with sudden onset. Other more severe signs tend to be the result of concomitant infections.

Production parameters are not Production parameters tend to be affected because there always affected. If they do is often a loss of appetite change, slow growth rate, Productive in the affected pens. The poor feed conversion rate, performance parameters affected are uneven growth in the litter or the same as in the endemic pen, and a protracted late fattening phase can be seen. form, although more severe.

The clinical expression of EP will largely depend on the immune status of the animal infected by M. hyopneumoniae. If the animal has been infected before and/or has been vaccinated, it

M. hyopneumoniae infection encourages coinfection by other

will probably show signs of the endemic form. Conversely, ani-

respiratory pathogens, leading to enzootic pneumonia (EP) or

mals with no immunity will probably exhibit the epidemic form.

porcine respiratory disease complex (PRDC), so the respiratory

In Europe, especially in the densely populated pig producing

disease often worsens. In these cases, dyspnoea and fever can

areas, the endemic form is the most common, due to continu-

be seen in addition to coughing; morbidity and mortality can

ous circulation of M. hyopneumoniae between farms and wide-

increase, affecting the animal’s productive performance signifi-

spread vaccination.

cantly. Two forms of EP can be distinguished, according to the clinical expression of the disease: the endemic form and the epidemic form (Table 1).

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2 What are the clinical signs of M. hyopneumoniae infection?

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Not all M. hyopneumoniae infections result in EP. In fact, one of the most important aspects of M. hyopneumoniae infection is its ability to cause subclinical, chronic and often persistent infection.

Figure 1. Dorsal view of a pig lung showing lesions consistent with M. hyopneumoniae infection. CVPC can been seen, affecting the left apical lobe, and both cardiac lobes. The right diaphragmatic lobe appears mildly affected.

PATHOLOGICAL DIAGNOSIS Lung lesions consistent with M. hyopneumoniae infection can have other causes, so an exhaustive assessment of these lesions must be made.

Although the macroscopic and microscopic lesions are highly consistent with M. hyopneumoniae infection, these are not exclusive, as various infectious agents and some non-biological factors can also cause or facilitate them.

Experimentally, CVPC has been seen from the first week p.i. onwards, reaching its maximum spread and severity approximately 4 weeks p.i. However, these lesions tend to resolve about 8 weeks p.i., sometimes forming fissures of fibrous tissue with shrinkage of

MACROSCOPIC LUNG LESIONS Porcine mycoplasmosis (PM) is characterised by areas of pulmonary consolidation, often well demarcated and more collapsed than the surrounding lung tissue of healthy appearance.

It mainly affects the areas of the lung (apical and cardiac lobes, and the cranial portions of the diaphragmatic lobes). Lesions also tend to be seen in the accessory lobe. The affected area can be distinguished visually as it acquires a dark red to greyish red colour, according to the chronology of the lesion. This

lung tissue.

In PM, when the surface of an area of consolidated lung tissue is sectioned, a catarrhal exudate can be seen in the airways. Conversely, when a mucopurulent exudate can be seen, the involvement of other respiratory pathogens is guaranteed, and the animal is probably suffering from EP. It is important to remember that M. hyopneumoniae infection is not the only cause of CVPC; other organisms, especially Pasteurella multocida and swine influenza virus, can also give rise to very similar lung lesions.

macroscopic pattern is called cranioventral pulmonary consol-

Assessment of CVPC usually involves the determination of its ex-

idation (CVPC) (Fig. 1).

tent, and various methods can provide a value for the severity of the lesions. The most widely used systems for quantifying CVPC, and their main characteristics, are shown in Table 2.

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4 What do we know about M. Hyopneumoniae strains?

PORCINE ENZOOTIC PNEUMONIA

Various strains of M. hyopneumoniae that differ in their genome

Genotyping techniques have enabled M. hyopneumoniae

and virulence have been discovered so far, but the implications

strains to be differentiated genetically. Despite their overall

and actual effects of this are still largely unknown.

genetic homogeneity, various DNA regions do vary, and are thus termed polymorphic. These are the regions that are

Importantly, in order for control measures to be more effective, a better understanding is needed on the variability between different strains of M. hyopneumoniae, and how this variability has an impact on the epidemiology of the disease.

analysed using genotyping techniques, and they are used to detect subpopulations (strains) of M. hyopneumoniae. One of the techniques that is most commonly used for this pathogen analyses paired clusters of gene sequences at specific loci called variable number tandem repeats (VNTR). More than one of these gene sequences is usually analysed, as shown in Fig. 1, where three loci are examined using multiple loci VNTR

DIVERSITY OF M. HYOPNEUMONIAE The dynamics of infection differ considerably under field conditions, and this leads to much variation in the clinical signs and lung lesions associated with enzootic pneumonia (EP). This variability has been attributed to factors such as coinfection, management, housing and environmental conditions, and to the fact that strains of M. hyopneumoniae may vary in virulence.

The latter has promoted the detection and genetic characterisation of M. hyopneumoniae isolates as a main objective for epidemiological studies. As a result, more information has been discovered about the diversity of M. hyopneumoniae strains.

M. hyopneumoniae strains are known to be genetically heterogeneous, but it is not yet clear whether there is an association between genetic variation and virulence.

analysis (MLVA).

VARIABILITY FROM COUNTRY TO COUNTRY OR REGION TO REGION Different M. hyopneumoniae strains have been detected in different countries, and on different farms in a particular region.

However, there are reports of regions or neighbouring farms where only one strain, or very similar strains, are in circulation. Overall results may seem slightly contradictory, but they depend to a certain extent on the accuracy of the genotyping technique used. No particular M. hyopneumoniae strain has yet been associated with a particular country or geographical region. It has been suggested that the proximity of farms and the mixing of animals of different origins could introduce new M. hyopneumoniae strains, increasing diversity. This means that M. hyopneumoniae strains are likely to be more heterogeneous in areas of intensive production and/or where there is significant trading of pigs (Fig. 2).

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4 What do we know about M. Hyopneumoniae strains?

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Figure 1. Diagram explaining the MLVA technique.

Figure 2. Diagram of a hypothetical situation with various M. hyopneumoniae strains (coloured circles) in an area with low production density, and another with high density.

LOW FARM DENSITY AREA Sample A

Sample B DNA extraction

DNA A DNA B 3 loci VNTR analysis by PCR

DNA marker

Electrophoresis gels1 Locus 1 Locus 2

Locus 3

1,200 bp 1,000 bp 900 bp 800 bp 700 bp 600 bp

HIGH FARM DENSITY AREA

500 bp 400 bp 300 bp 200 bp

A

100 bp

B

A

B

A

B

Sequencing. Number of amino acid repeats2 Locus 1 Locus 2 Locus 3 MLVA3 results Strain A: 3–6–12 Strain B: 7–10–2 The three DNA regions amplified (loci 1, 2 and 3) have different molecular weights in samples A and B. 1

2 The number of amino acid repeats can be inferred from the size of these fragments. If sequencing is used, the repeats can be counted accurately.

3 Each strain is defined by the number of repeats at each of the loci analysed.

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4 What do we know about M. Hyopneumoniae strains?

PORCINE ENZOOTIC PNEUMONIA

VARIABILITY ON AN INDIVIDUAL FARM More than one strain of the pathogen can be found on a farm

Figure 3. Diagram of the respiratory organs of the pig, showing the different M. hyopneumoniae strains that have been detected in a single individual so far.

or in a herd, even when animals are vaccinated against M. hyopneumoniae. The M. hyopneumoniae transmission cycle can be interrupted in all-in/all-out production systems, so it has been suggested that there could be less variability in the M. hyopneumoniae strains circulating on farms that follow this production system than on farms with continuous production, where it seems to be easier to introduce new strains and for them to persist.

Up to 13 different strains of M. hyopneumoniae have been detected in one batch of pigs.

Different strains found in different locations in the same animal

VARIABILITY BETWEEN PIGS One individual can be affected by multiple strains of M. hyopneumoniae. This heterogeneity has been observed both in cases of infection by M. hyopneumoniae alone, and where there is coinfection with other pig pathogens. Different strains have also been detected in the same anatomical location (e.g. the lung) in an individual, and in different locations (e.g. the lung and trachea) in the same animal (Fig. 3).

Different strains found in the same location in the same animal

Up to 3 different strains of M. hyopneumoniae have been found in one single animal.

features of both types are summarised in Table 1. On farms, the

HOW DOES THE DIVERSITY OF STRAINS AFFECT CLINICAL PRESENTATION?

lesions and its effect on the onset and duration of clinical signs

Experimentally, M. hyopneumoniae strains have been clas-

lung lesions, but this additive effect has not been confirmed

sified into high- and low-virulence strains: the distinguishing

by other studies.

effect of M. hyopneumoniae variability on the severity of lung has yet to be clearly defined. Some studies have indicated that coinfection by more than one strain results in more severe

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4 What do we know about M. Hyopneumoniae strains?

PORCINE ENZOOTIC PNEUMONIA

Currently, the lack of a known genetic marker for virulence, combined with the existence of different strains, makes it difficult to understand the effect of strain variability on clinical presentation, both at an individual and farm level.

Table 1. The distinguishing characteristics of high and low

virulence strains of M. hyopneumoniae have been described in various experimental studies.

High virulence strains

Low virulence strains

More pronounced cough and earlier onset of clinical signs

No cough. When there is cough, it is less severe and starts later

Production parameters

Variable effect on daily weight gain

Unaffected in most cases

Lung lesions

More animals affected.

Lesions are more severe

Fewer animals affected.

Lesions are less severe

Seroconversion

M. hyopneumoniae antibodies usually appear at an early stage (seroconversion closer to infection)

M. hyopneumoniae antibodies usually appear at a later stage (seroconversion further from infection)

Immunogenicity

Stronger proinflammatory effect, with more cytokine production and inflammatory cell infiltration at a local level

Weaker proinflammatory response

EFFECT OF VARIABILITY ON VACCINE EFFICACY

Multiplication

Higher multiplication rate.

Possible dissemination to other internal organs

Lower multiplication rate.

Dissemination to other internal organs not reported

Antigenic differences between M. hyopneumoniae strains have

Adhesion

The existence of different strains of the pathogen could have significant repercussions on the efficacy of control and prevention methods (vaccination and/or antibiotic treatment),

Clinical signs

and on the sensitivity of diagnostic techniques. However, these aspects are still largely unknown.

The importance of M. hyopneumoniae variability and the implications for the pig sector are still to be determined.

been reported, and this could mean that the antibody profile generated by a vaccine strain may not be exactly the same as that generated by circulating field strains. This would suggest that the degree of protection provided by a vaccine could partly depend on its similarity to the infection strain. Despite this, an experimental study compared the protection offered by a homologous vaccine (vaccine strain identical to the inoculation strain) and a heterologous vaccine (vaccine strain different from the inoculation strain). No conclusive differences were found regarding the level of protection conferred.

Transmission Adaptation to in vitro culture medium

No significant differences No significant differences Expression of more proteins related to adhesion and colonisation of the pig’s respiratory tract

Expression of more proteins related to metabolism and growth

Beatriz García-Morante, Joaquim Segalés and Marina Sibila, SUIS no. 115, 2015.

challenged with a low virulence strain. The comparison was made with a non-vaccinated control group. This could be because highly virulent strains induce a more severe inflammatory response (and therefore lesions), and thus would be more likely to show a greater difference from the control group. Another trial also demonstrated

The fact that the most virulent strains can be more immunogen-

the efficacy of a commercial vaccine against coinfection with two

ic (Table 1) could have consequences for vaccination. One tri-

different M. hyopneumoniae strains, one of high virulence and the

al using a commercial vaccine suggested it was more effective

other of low virulence.

in animals challenged with a high virulence strain than in those 52

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PORCINE ENZOOTIC PNEUMONIA

5 What happens after infection?

Table 1. Potential risk factors for M. hyopneumoniae infection described in the literature.

DISEASE RISK FACTORS Enzootic pneumonia (EP) onset and severity are affected by various factors (Fig. 1) and it is important to understand these

Risk factor

in order to control the disease. Various risk factors have been

Weather conditions

described at an individual and farm level that seem to increase the probability of animals being infected and going on to develop

Geographical location of the farm

EP (Table 1).

Production system

The risk factors identified for M. hyopneumoniae infection highlight that the approach to prevent and control EP must be multifactorial and tailored to each individual farm.

Repopulation policy

Housing Sow parity

Figure 1. Factors potentially affecting the onset and severity of EP in pigs.

Management

Coinfection (other bacteria)

Host

PORCINE ENZOOTIC PNEUMONIA

Management during breeding stage

Weaning management strategy

Definition

• • • • • • • •

High rainfall.

Low temperatures.

Proximity to other pig farms.

Proximity to a road.

Continuous flow.

Frequent entry of replacement gilts (>120/year).

Poor acclimatisation of gilts and boars.

No vaccination against M. hyopneumoniae during acclimatisation.

• •

High pen stocking rate.

High number of pens per barn in farrowing accommodation (>16 pens).

• • • • • •

First or second gestation.

•

No vaccination against M. hyopneumoniae.

High fostering rate.

Long lactation period.

Low temperatures in piglet bedding area.

Piglet teeth not clipped/ground.

Piglets only given one dose of iron.

The greatest risk for introducing M. hyopneumoniae into a farm that is negative for the pathogen is the entry of infected animals.

Environment

Once these critical factors are known, the likelihood of pathogen transmission and infection can be reduced. In endemic situations, piglets infected by M. hyopneumoniae are considered to

Primary agent (M. hyopneumoniae)

be the initiators that spread the disease. Identifying risk factors during the suckling period could help create intervention strategies to prevent M. hyopneumoniae transmission from sows to their progeny and, therefore reduce the effect of the disease in fattening units.

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