Swine parasitosis – Neonatal coccidiosis, Diagnosis
It is important to know the biological cycle of Isospora suis to understand the diagnosis, treatment and prevention of porcine neonatal coccidiosis. For this reason this article briefly explains the life cycle of the parasite, in addition to citing the main techniques to be taken into account for the diagnosis of this pathology.
I. Suis presents a direct biological cycle (with a single host) that consists of two differentiated stages:
– Exogenous phase: the oocyst, which is expelled to the outside along with the feces, needs to sporulate in the environment to be infective. Once sporulated, if it is ingested by another pig, it will perform the endogenous phase.
– Endogenous phase: In the intestinal lumen, the oocyst releases sporozoites that colonize epithelial cells of the small intestine. Within the enterocytes, sporozoites replicate asexual (merogony) and sexual (gamogony), breaking the cells and colonizing new ones to initiate a new reproductive cycle. The destruction of the cells due to the replication of the parasites is the origin of the clinical signs of neonatal coccidiosis.
Image 1. Biological cycle of I. suis
Cells derived from sexual reproduction (micro and macrogametes) fuse together resulting in a zygote, which will become an oocyst and be excreted with feces, thus closing the parasite cycle.
From ingestion of the oocyst to the occurrence of non-sporulated oocysts in feces, it takes 4 to 6 days, which means that the excretion of contaminated feces will take place in piglets from 4 days of age.
Clinical signs of porcine neonatal coccidiosis are typical of a mild gastrointestinal condition, so farmers often refer to parasitism as "a non-antibiotic-like colibacillosis-like diarrhea."
For this reason, the diagnosis can not be based solely on the clinical signs and the clinical history of the farm, but other techniques are necessary to identify I. suis as a pathogen present on the farm.
It is important to evaluate the presence of other pathogens to eliminate other causes of diarrhea, in addition to taking into account that, sometimes, I. suis is present along with other primary or copatogenic pathogens that may aggravate the clinical signs.
Coprology consists of determining the presence and quantity of oocysts in the feces of animals. It is not always indicative of clinical infection, since coccidios are ubiquitous in many pig farms. For this reason, although coprology is an accepted technique for the diagnosis of coccidiosis, it is not considered the most sensitive and reliable.
Samples suitable for identification of oocysts must be taken from piglets that have suffered diarrhea for at least 2 days, since clinical signs usually occur before the excretion of oocysts in feces. Pasteous stools usually contain more oocysts than liquid stools.
Image 2. Sporotic oocyst of I. suis (coprology)
To quantify the number of oocysts, it is advisable to count using the McMaster technique with a saturated saline solution.
Necropsies can be performed on affected piglets to determine the presence of lesions and / or parasites in the small intestine. Unlike coprology, the demonstration of parasitic stages in samples of intestinal tissues is sufficient to obtain a diagnosis.
Usually, lesions are restricted to the intestinal tract, especially jejunum and ileum; Although occasionally the duodenum, cecum, or colon may be affected.
The severity of the lesions is variable, since it depends on the number of oocysts ingested. In mild infections the bowel is usually turgid and there may be mild fibrinous enteritis in small segments of the small intestine, whereas in severe infections there may be fibrinonecrotic enteritis
The most reliable diagnosis is the identification of coccidia in histological sections of the intestine: several areas of jejunum and ileum mucosa should be examined to maximize the sensitivity of the histological examination, since the distribution of microscopic lesions and parasites is unpredictable.
Microscopically, necrosis and atrophy and fusion of some villi of the intestinal mucosa are observed, as well as hyperplasia of the epithelium of the crypts and elongation of the same.
Image 4. Giemsa stain of the intestinal epithelium of the jejunum (piglet). Asexual phase: meronte and merozoites (large and medium arrow, respectively). Sexual phase: macrogametos (small arrow).
Image 3. Fibronecrotic enteritis due to coccidiosis.
Identification of parasitized cells with different stages of I. suis can be performed by staining with the Giemsa method of the intestinal mucosa samples.
MV. Júlia Pié Orpí
Veterinary Technical support to the area of Latin America at Biovet S.A. Laboratories Official Veterinary Services (SVO) in poultry slaughterhouse