# Presentation: 486180

## Mycoplasma hyopneumoniae Associated Respiratory Disease on the Farm 

**Brad Thacker**
**Iowa State University**

## Mhyo: General Characteristics

- Obligatory pathogen of the respiratory tract of the pig
- Infection is limited to the airways
*Mhyo* by itself causes little if any reduction in performance
- Recognized as an initiator or potentiator of more serious respiratory diseases caused by other primary or opportunistic pathogens

## Mhyo: General Characteristics

- Does *Mhyo* potentiate the impact of bioreactive environmental contaminants such as endotoxins and glucans?
*Mhyo *infected herds are at greater risk for developing respiratory disease compared to *Mhyo*-free herds

## Mhyo: General Characteristics

***Mhyo***** utilizes several mechanism to cause disease**
- Respiratory immune system modulation
- Attraction of lymphocytes
- Cytokine profile
- Cilia atrophy resulting in reduced function of innate defense mechanisms

## Impaired Innate Defenses

**Mucociliary apparatus dysfunction**
*Mycoplasma hyopneumoniae* causes cilia atrophy
- Dehydration decreases fluid layer => reduced cilia activity
- Ammonia inhibits cilia movement resulting in reduced clearance of bacteria
- Carbon dioxide/monoxide effects?
**Disruption makes pigs more prone to developing pneumonia**

## Mhyo: Historically

**Clinical presentation**
- Chronic, low-to-moderate grade pneumonia
- Variable morbidity
- Reduced growth rate
- Low mortality
- Recognized in finishing pigs
**Characterized as “enzootic pneumonia”**

## Mhyo: Historically

*Mhyo* was believed to be the primary cause of enzootic pneumonia
- Opportunistic bacteria, especially *Pasteurella multocida* (Pm) were believed to be “secondary invaders”
**Relative contribution of each bacteria was difficult to ascertain**
- Pm was not a concern in *Mhyo *free or “quite” herds

## Mhyo: Historically

**Explosive outbreaks of respiratory disease were attributed to SIV, App or a “hot” *****Pasteurella***
- SIV was a minor, periodic problem
- Differentiate from PRV
- App was the “profit robber”
- Mixed sources of feeder pigs
- Poor understanding of environmental triggers
- Poor understanding of vaccinology (ApX toxins)

## Mhyo: Historically

**Diagnostics**
- Few laboratory capabilities
- More veterinary contact => better clinical assessment
- Fewer records => less production and economic data
- Slaughter checks used but didn’t understand how to interpret the data very well
- In total, relatively subjective evaluations

## Mhyo: Historically

**Control**
- No vaccines
- All-in-all-out by room
- Periodic medication for secondary invaders
- Pulse one week every month (CTC/BMD rotation)
- During stress periods
- Weaning
- Move from nursery to finisher
- Many farms had more than two phases
- Based on severity of disease: vet evaluated
- Better diets, ventilation, pig flow

## Mhyo: Historically

- Subjective evaluations => “Seat of the pants” approach
- Limited factors to control
**However, NOT uniformly ineffective!!**
- No PRRS virus
- Smaller herd sizes
- Smaller room sizes => better microenvironments?

## Mhyo: Currently

**Evolution of swine respiratory disease**
- More explosive, but repeated outbreaks
- Somewhat older pigs (16-20 weeks of age)
- Predictable age at onset
- High morbidity
- Increased stall-out pigs
- Variable, but sometimes high, mortality
**Designated as the “porcine respiratory disease complex” (PRDC)**** **

## Mhyo: Currently

**Common organisms isolated from PRDC cases besides *****Mhyo***
- PRRS virus
- Swine influenza virus (SIV)
*Pasteurella multocida* (Pm)
- Porcine circovirus Type 2 (PCV2)
*Actinobacillus pleuropneumoniae, A. suis*
*Salmonella cholerasuis*
*Hemophilus parasuis* and *Streptococcus suis*

## Mhyo: Currently

**The main difference between enzootic pneumonia and PRDC?**
_***Viruses!!***_
- PRRSV
- Changing pattern of SIV
- PCV2?

## Mhyo: Currently

*Mhyo* often plays a significant role in the underlying severity of PRDC or enzootic pneumonia
*Mhyo* vaccination tends to be beneficial in herds with varying degrees and presentations of respiratory disease

## Mhyo Vaccination Field Study

**14 herds in Belgium**
**Vaccinate at 1 and 4 weeks of age**
**Improvements**
- Daily gain (+22g) and FCR (-.07)
- Decreased medication costs ($1.02); greatest benefit
- Prevalence (-14%) and lesions (-3%) at slaughter
- None- mortality, coughing, carcass quality

## Why PRDC vs. enzootic pneumonia?  What has changed?

**New agents**
**PRRS virus!!**
**Pig flow**
- Increasing herd size
- Age segregated rearing, multiple site production
- Reduced weaning age?!
**Less attention to pig comfort**
- Especially in the nursery => more poor pigs
**Phase feeding**
- Potentially more pigs on the wrong diet

## Pig Flow Related Issues

**Benefits of AIAO and SEW were demonstrated in small herds and/or small scale research projects**
- Bacterial disease control is the primary benefit
- Viruses have emerged as important contributors
- Prevention of vertical transmission via early weaning results in highly susceptible populations of finishing pigs
- Prevention of lateral transmission via AIAO results in highly susceptible populations of finishing pigs

## Pig Flow Related Issues

**Applicability to large herds/systems**
- Continual pathogen circulation in breeding herd
- Compliance with pig flow rules (weaning age)
- Multiple sites: many finishers close together, viruses transmitted between sites (PRV, SIV, PRRSV)
- High capital investment => keep facilities full => no flexibility to eliminate disease via sequential depopulation => continual disease

## Pig Flow Based Disease Control

**Disease level will continue to increase unless the cycle is broken**
- Pre-PRRS:
- Sequential depopulation of rooms within a building was reasonably effective for bacterial diseases
- Post-PRRS:
- Sites need to be depopulated to move disease out

## PRDC Prevention and Control

**Multi-factorial approach is necessary**
- Management, sanitation, nutrition, pig flow, growth promoters and environment
- Improve disease status and productivity in a general sense
- Medical: vaccination, acclimatization of new animals and therapeutics
- Reduce the impact of specific diseases

## PRDC Prevention and Control

**Multi-factorial approach is necessary**
- Recognize that some diseases or deficiencies can be dealt with and some can’t
- Available technology
- Cost considerations: can’t afford every product
**Strategy => success**
- Aggressive = do everything possible
- Conservative = change one thing

## Clinician’s View of Diagnostics

- Identifying all of the organisms present in a given situation is essential
**The clinician’s challenge is sorting out the relative role that each organism plays**
- Tissue level: histopath
- Organ level: extent of lesions
- Animal level: severity of signs, organs damaged
- Herd level: number of animals affected and severity
**Determine economic impact to justify action**

## Clinician’s View of Diagnostics

- Gross (visible, macroscopic) lesions are of little diagnostic value except in App cases
- Main decision in acute outbreaks: App or not?
- Lesions of *Mhyo,* SIV and in a recent case of PRRSV/circovirus look the same
- Must verify cause of lesion by histopath and organism identification

## Question: Is this mycoplasma?

## Swine Influenza Virus

## Clinician’s View of Diagnostics

**Clinical signs are not characteristic of any one disease or disease combinations**
- Fever
- Cough
- Increased respiration rate
- Dyspnea

## Clinician’s View of Diagnostics

**With enzootic pneumonia, diagnosis was often limited to necropsy lesions with very little laboratory testing**
- Were our assessments correct?
- Did we truly understand the role of the various organisms involved?
- Likely not
**Are we doing better with PRDC diagnostics?**** **

## Diagnostic Sampling Strategies

**Small numbers of pigs tested will result in missed diagnoses**
- PRDC case: 21 finishing pigs of various ages submitted for necropsy
- Pathology/microbiology:
**No lesions =5**		Gastric ulcer = 2
- PMWS = 5		PRRSV = 2
- SIV? = 1			App? = 3 (non-typeable)
*P. mult.* = 2		*Bordetella* = 2
*Strep suis* = 1		*M. hyo* = 8
- Serology: *M. hyo*+, SIV+, PRRSV(late +)
- Slaughter check: Low average percent pneumonia, a few pigs with severe A-V pneumonia

## Clinician’s View of Diagnostics

- The severity of pneumonia observed at slaughter may have little relationship to the impact of pneumonia on life time health status and growth performance
**Lesions resolve with time:**
- SIV => quickly (2-3 weeks)
*Mhyo* => slowly (2-3 months)

## Clinician’s View of Diagnostics

- Few production systems can monitor daily feed and water intake, which can pinpoint when disease is affecting performance
- Unable to detect short time periods of reduced performance that significantly contribute to reduced close-out based performance
- Vaccination, prevention, control decisions ultimately are based on economics
- Costs are relatively easy to determine
- Benefits (reduced disease impact) are difficult to determine

## Summary

**Still not smart enough to effectively control respiratory disease in swine**
- Pathogens
- Environmental stressors
- Economics
**Every herd situation is unique**
- Diagnostics and remedial actions need to be implemented on a farm-by-farm basis
- “Cookie cutter” production/medical approach does not work very well

## Summary

**Laboratory research and diagnostic testing frame the questions for and define the limits of the clinician’s approach to each situation**
**The final answer ultimately lies with the attending clinician, who makes the diagnosis and formulates, implements and monitors treatment and control programs**