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Detection of enteric pathogens in newborn piglets (1/2)

The ideal sample for diagnostic of neonatal enteric pathogens is the submission of live piglets.

Monday 6 October 2014 (4 years 5 months 15 days ago)
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Neonatal diarrhea is one of most frequent condition observed in conventional swine production systems around the world. The great majority of the causes of neonatal diarrhea are infectious and directly related to improper routine cleaning and disinfection management practices. The common rule of maximal use of facilities had put an enormous pressure on the production scale of the farrowing house and consequently reduced or extinguish the downtime of cleaned and disinfected crates. The final consequence is an extremely high pressure of infection, causing recurrent infectious diarrheic problems, that is always tried to overcome with the use of the most advanced detergent and/or disinfectant. However, at the end of the day, there is nothing similar to proper washing and desiccation by downtime. The infectious agents associated with this situation are more frequently enterotoxigenic Escherichia coli (ETEC), Rotavirus A, B and C, Clostridium perfringens type A and C, Clostridium difficile and Isospora suis. Coronavirus infections such as Transmissible Gastrenteritis virus (TGEv), Porcine Epidemic Diarrhea virus (PEDv) and Delta coronavirus are pathogenic enough to cause problem even in tide management conditions, but are worsen in situation of poor cleaning management.

Newborn piglet

The first step for a successful diagnostic of infectious newborn diarrhea is the selection of animals. Always choose the piglet that had just started with clinical diarrhea but it is not lethargic or dehydrated yet. Selecting animals at the beginning of the course of the disease might be the critical point between the detection or not of mainly viral agents such as Rotavirus and Coronavirus. The amount of viral particles in enterocytes of recent infected animals is much higher than in chronic piglets. Chronically infected piglets will have lost the epithelium over layer of the crypts, and consequently it would be more difficult to find virus antigen and/or RNA.

The ideal sample for diagnostic of neonatal enteric pathogens is the submission of live piglets. As histopathology is the main stream of the diagnostic procedure, time after death and autolysis are major impediments for adequate evaluation of histologic lesions and detection of infectious agents in enteric cells. For instance, 20 to 30 minutes after death there is diffuse detachment of enterocytes from the tip of villi due to autolysis, what makes impossible the histologic diagnostic of ETEC and I. suis. Two hours post mortem, all tissue from the middle to the tip of the villi became eosinophilic with no distinction among cells due to autolysis. As the great majority of samples arrive at the diagnostic laboratory the day after collection, the submission of only fresh intestinal samples would significantly limit or even prevent proper histological evaluation. As a result, it is imperative, if you are not submitting live animals to diagnostic laboratory, to collect intestinal samples just after piglets’ euthanasia for histopathology. Intestinal fragments of 2 to 3 cm in length, from two portions of ileum, four to five sections of the jejunum, one fragment from cecum, one fragment of proximal colon and two fragments from spiral colon have to be formalin fixed (10% formalin) in plastic bags or plastic buckets. Also collect mesenteric lymph nodes and liver fragments for histopathology. All these samples will be used for histopathology evaluation, and in some cases, also for immunohistochemistry (PED, TGE, Rotavirus) or in situ hybridization (ISH).

In addition to formalin fixed samples, it is important to collect and submit fresh samples for bacteriology, virology and molecular biology tests. Fragments, 10 to 15 cm in length, of ileum, jejunum, and remain portions of cecum and spiral colon have to be stored in a plastic bag. Mesenteric lymph nodes and liver fragments also should be collected and stored in a different bag, in order to avoid contamination.

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