Isolation of Actinobacillus pleuropneumoniae

Isolation of Actinobacillus pleuropneumoniae from tonsils of pigs 1 to 4 weeks  age commercial farm.

² Department of Biological Sciences, Faculty of Higher Cuautitlán, UNAM,   
³ FMVZ Autonomous University of Puebla

Introduction

Contagious swine pleuropneumonia is a worldwide disease caused by Actinobacillus pleuropneumoniae (APP) coccobacillary Gram negative bacteria. It is characterized by causing fibrin-necrotic pleuropneumonia because of the action of lipoprotein capsular even four different RTX toxins, called Apx (Apx Apx-I-IV) ^1.

 APP transmission occurs by direct contact or spray at close range,   through infected mothers or carrier pigs, allowing the colonization of the tonsils and alveolar epithelium.

The clinical presentation of the disease occurs when APP proliferates in lung tissue, supported by predisposing factors such as poor ventilation, heat stress, high microbial environmental burden, immunosuppression and circulation of viral or bacterial agents that damage the lungs and airways.

In the pathogenesis of lung tissue damage pleuropneumonia is a direct consequence of the Apx toxins,   generating alveolar epithelial injury with   cell necrosis and acute inflammatory response. Pulmonary endothelium is also injured blood vessels, causing thrombosis and infarctions and favors the formation of fibrinous exudate.  

The acute clinical course of the disease is characterized by fever, respiratory distress, cyanosis, abdominal breathing "jump", epistaxis and hemoptysis besides anorexia. Morbidity and mortality are usually greater than 10%.   The severity of the clinical picture may vary according to serotype, the microenvironmental conditions and primary stakeholders. Pigs that survive the acute process develop chronic course with persistent pneumonia, abdominal breathing and stunted.

 At necropsy the most characteristic lesions are cyanosis of the corpse, fibrinous pleuritis with pleural adhesions, fibrin-necrotic cranio-ventral or diffuse with red caudal lobes infarcts pneumonia. Recovered pigs have fibrous adhesions in pleura.   

The diagnosis is made ​​with data from clinical signs, morbidity and mortality, injuries at necropsy and histopathology, bacterial isolation and serology. For the serological diagnosis ELISA for detecting antibodies anti-Apx IV, which identifies clinically recovered pigs, and agglutination tests to detect carrier pigs and serotype that is infecting pigs is performed.

This study was conducted to isolate APP macerated tonsils of pigs 1-4 weeks of age of a commercial pig farm to determine the prevalence of infection and weeks of age to which colonization is detected.

Material and methods

The study was conducted on a farm of 2000 bellies, positive for infection with APP. Four groups of 15 dead pigs were established corresponding week   1 to 4   age, necropsy was performed and tonsil aseptically recovered. They were kept frozen at -20 ° C until planting.a maceration was performed with the tonsils and the supernatant was cultured on blood agar media with groove nurse Staphylococcus aureus   and BHI agar supplemented with NAD factor that helps in determining the dependence ofActinobacillus pleuropneumoniae   to this factor. Bacterial growth was purified and identified with biochemical primary and secondary testing.

Results

The isolation of Actinobacillus pleuropneumoniae was obtained from the first week of age, with 26% positive samples in the case of positivity in the 2nd, 3rd and 4th week was 20%, 33% and 46 % respectively  

Discussion
It was determined that APP is able to colonize the pigs from the first week of age, according to Fenwick ² Marsteller and indicates this possibility when pigs are infected in maternity.

It has been established that APP is a late colonizer. It is considered that a weaning age 10 days reduces the risk of colonization up to 90%,   and weaning at 16 days reduced by 50% the risk of encountering a colonized pig. These colonization rates may vary according to maternal immunity, but in this work July 30 positive samples total samples of the first two weeks of life were taken, representing a 23.3% prevalence.

In breastfeeding transmission of infection can be attributed to the mother pig, because it is the nearest source of contamination by direct contact of APP, especially if the divisions between a cage maternity and other are of a solid material. In the case of metal wire panel   transmission is possible among a litter of piglets to another. It should be considered an investigation into the possibility of spread of infection based on the variable construction material of the cage.

Even in the presence of maternal immunity colonization is observed, which determines the risk of sending infected sites 2 and 3, with the consequent possibility of developing the disease pigs.

These results force us to assess the segregated early weaning protocols that aim to eliminate APP. According to Muirhead and Alexander ²   not so premature settlements were developed, so the possibility of weaning of less than 21 days of lactation without the risk of transmission of infection is established, however our findings show us this possibility of early infection, so it is essential to have a medication protocol that meets this objective.

The mashing process of tonsillar tissue is a suitable method for the isolation of APP   usually used in experimental studies 3 and in this paper was applied to pigs that are part of routine maternity mortality, so it is a useful diagnostic strategy for research and development   on APP on commercial farms.  

References

1. Gottschalk M., Taylor DJ, Actinobacillus pleuropneumoniae, in: BE Straw, JJ Zimmerman, S. D'Allaire, Taylor DJ (Eds.), Diseases of swine, Blackwell Publishing Professional, Ames, Iowa, USA, 2006 pp. 563-576.

2. Marstseller TA ,. Fenwick, B: Actinobacillus pleuropneumoniae disease and serology. Swine Health Prod 1999 (7):. 161-165.

3. MR Muirhead, Alexander TJL: Managing and treating disease in the weaner, grower and finishing periods.   In Managing Pig Health and the Treatment of Disease, 2007; p. 294. Sheffield: 5M Enterprises Ltd.  

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