Necrotic enteritis in broiler breeder chickens associated with Ascaridia galli
Andrew Brooks, Jacob Avula, Kathleen Sary
Animal Health Laboratory, University of Guelph, Guelph, ON (Brooks, Avula), Maple Leaf Foods (Sary)
AHL Newsletter 2020;24(4):13.
A commercial broiler breeder operation reported an increase in mortality after young males were recently introduced (commonly called spikers). Only new males added to this mature flock were affected and mortality started about two weeks after their arrival. Four dead young males were submitted to the AHL for postmortem. Three out of four birds had characteristic lesions of necrotic enteritis (NE) with thick layers of necrotic debris lining the jejunum. One bird with no intestinal lesions had pulmonary hypertension syndrome (ascites). No coccidia were observed in several wet-mount preparations of scrapings of the intestinal mucosa but a few nematode larvae were visible. No adult nematodes were present in the intestinal tracts and there were no other significant gross findings.
Histopathology of the small intestine revealed lesions typical of NE, including areas of mucosal necrosis containing plump bacilli, and large numbers of Clostridium perfringens were isolated from the lesions. Interestingly, the affected intestine also contained many parasite larvae burrowing in the mucosal lining (Fig. 1). One section of intestine also contained rare coccidia. The AHL Parasitology laboratory identified numerous ascarid larvae consistent with Ascaridia galli in scrapings of the intestinal mucosa (Fig. 2). No gastrointestinal nematode eggs or coccidia oocysts were detected in the flotation of a pooled fecal sample.
A. galli is a common parasite of chickens that also infects turkeys, geese, ducks and wild galliform birds (1). The adult parasites are large white roundworms that inhabit the lumen of the small intestine. Male and female adults range in size from 50-75mm and 70-120mm respectively. The life cycle of A. galli is a direct one. Birds become infected by ingesting infective eggs in the environment. Following ingestion, the eggs hatch and larvae mature and burrow within the lining of the intestine during the prepatent period. Adult worms in the intestine lumen may live for one year and shed eggs into the environment via the feces. The eggs become infective to other birds after approximately three weeks under optimal environmental conditions. Ascaridia eggs are quite hardy and can survive for several months in cool, moist environments such as poultry litter.
A. galli is not considered highly pathogenic. The majority of infections are asymptomatic, especially in adult chickens. In young chickens, a heavy burden of larvae may produce diarrhea, anemia and reduced weight gain as the parasites migrate within the intestinal lining. Large numbers of adult Ascaridia may also physically obstruct the intestine (1).
In the absence of a significant burden of coccidia, the large number of A. galli larvae are a likely predisposing factor to the development of NE in this case, similar to the role of Ascaridia dissimilis in turkeys (2, 3). The birds in this submission may have been immunologically naïve and perhaps were exposed to large numbers of ascarid eggs upon joining this established flock. This submission highlights the multifactorial nature of NE and the importance of helminth control programs.
Figure 1. Numerous larvae of Ascaridia galli (arrows) burrowing in the mucosa of the small intestine (inset: higher magnification of larvae). (H&E)
Figure 2. Ascaridia galli larval stage detected in the mucosal scrapings of the small intestine.
References
1. Taylor MA, Coop RL, Wall RL. Veterinary Parasitology, 4th ed. Wiley Blackwell, 2016:74-75, 684-685.
2. Brash ML, Stalker MJ, Weber L. An uncommon cause of necrotic enteritis in a flock of 7-week-old Ontario meat turkeys. AHL Newsletter 2014;18(2):15.
3. Norton RA et al. High Mortality of Domestic Turkeys Associated with Ascaridia dissimilis. Avian Diseases 1992;36:469-473.