Re-evaluation of the life cycle of Eimeria maxima Tyzzer, 1929 in chickens (Gallus domesticus)

Authors: Dubey, Jitender; Jenkins, Mark

Submitted to: Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2017
Publication Date: 12/14/2017
Citation: Dubey, J.P., Jenkins, M.C. 2017. Re-evaluation of the life cycle of Eimeria maxima Tyzzer, 1929 in chickens (Gallus domesticus). Parasitology. https://doi.org/10.1017/S0031182017002153
DOI: https://doi.org/10.1017/S0031182017002153

Interpretive Summary: Avian coccidiosis is an intestinal disease caused by protozoa in the genus Eimeria. Each year, the disease incurs over $350 million loss in the U.S. alone, and over $1 billion worldwide due to poor weight gain in infected chickens and the cost of administering anticoccidial drugs and vaccines. The most costly parasite is Eimeria maxima because it not only depresses weight gain and feed utilization, but also predisposes chickens to other diseases such as necrotic enteritis, a bacterial disease that causes high mortalities in young chicks. Although the parasite was described over 90 years ago, there is conflicting information on where in the gut the parasite invades and how the parasite replicates within the intestine. The purpose of this study was to describe the development of the parasite in chickens to understand its effects on growth. Contrary to previous studies conducted over the last century, our studies revealed that the parasite localizes to an area of the gut involved in nutrient absorption. While there it undergoes at least 4 stages of replication with destruction of the gut surface. This information will be valuable to poultry and pharmaceutical companies that are considering control measures against avian coccidiosis caused by E. maxima.

Technical Abstract: There is uncertainty concerning the developmental stages of the poultry coccidium, Eimeria maxima. To resolve this, broiler chickens were inoculated orally with 5 million E. maxima oocysts and were necropsied 12, 24, 36, 48, 60, 72, 96 or120 h p.i. Small intestine tissue sections and smears were examined for developmental stages. Jejunum was the highest parasitized region. At 12 h p.i., sporozoites inside a parasitphorous vacuole (PV) were observed in the both the epithelial villi and lamina propria. By 24 h, sporozoites enclosed by a PV were observed in enterocytes of the glands of Lieberkühn. At 48 h p.i., sporozoites, elongated immature and mature schizonts were all seen in the glands with merozoites budding off from the main schizont. By 60 h, 2nd generation sausage shaped schizonts containing up to 12 merozoites were observed around a residual body in the villar tip of invaded enterocytes. At 72 and 96 h, profuse schizogony associated with 3rd and 4th generation schizonts was observed throughout entire villus. At 120 h, another generation of schizonts were seen in villar tips as well as in subepithelium where, gamonts and oocysts were also present. These findings explain in part the clinical effects observed during E. maxima infection.