Case Studies: Infectious diseases in Pigs

Jackie Picard

7 Case Studies: Infectious diseases in Pigs

Investigations into Infectious diseaseS in growing pigs

Introduction

Most commercial piggeries manage large numbers of pigs, from breeding through to the production of porkers and baconers. Because pigs live in close quarters and experience production-related stresses, they are vulnerable to various infectious diseases at different stages of their lifecycle—particularly those caused by endemic agents. In these case studies, you will examine diseases of the gastrointestinal and respiratory tracts that negatively affect the productivity of pigs during their growing phases.

Case (Tasks A to C): Scouring in weaned piglets

Case History

A commercial piggery in Victoria was finding that there was an increase in scouring pigs of 6 to 12 weeks old. These pigs were also not gaining weight or growing as expected.

You suspect the following bacterial pathogens:

Enterotoxigenic Escherichia coli
Salmonella enterica serovars
Lawsonia intracellularis
Brachyspira hyodysenteriae
Brachyspira pilosicoli

Task A: Bacterial pathogenesis

For each suspected pathogen (ETEC, Salmonella enterica, Lawsonia intracellularis, Brachyspira hyodysenteriae and Brachyspira pilosicoli):

Describe its key virulence factors.
Explain how these factors contribute to disease in pigs.

Task B: Identifying the cause

Design a decision tree that will help you distinguish between these causes based on the pig’s age, clinical signs and histology typical for each agent. You have already made decision trees in the case studies dealing with granulomatous disease in animals.

Task C : Control strategies

Outline strategies to prevent and control these diseases in a commercial piggery setting. Include biosecurity, vaccination, and management practices.

Case D : Chronic respiratory disease in a Pig

A finishing pig enrolled in a vaccination trial against enzootic pneumonia and porcine circovirus type 2 developed a chronic dry cough. The pig was euthanized for examination. Gross pathology revealed cranioventral consolidated, plum-coloured areas in the lungs, consistent with catarrhal and suppurative bronchopneumonia. PCR testing of lung tissue was negative for PCV2, Actinobacillus pleuropneumoniae, and Glaesserella parasuis, but positive for Mesomycoplasma (Mycoplasma) hyopneumoniae and Pasteurella multocida.

Questions

What was the primary disease affecting this pig? Explain your reasoning based on the lesions and PCR results.
What characteristics of Mycoplasma species make them well-suited for causing chronic respiratory disease? Discuss morphology, surface structures, virulence factors, and mechanisms of pathology.
Why might the vaccine have appeared ineffective in this case? Consider timing, immune response, and pathogen interactions.