Coccidiosis is a single-celled host-specific parasite, most coccidioides in birds belong to the compound apical phylum, Amelia spp., and Coccidioides amyogenesis is generally described by the morphology of the oocyst (zygote of coccidioides) excreted with the feces of the infected host.
The egg sac is wrapped in a thick shell, composed of a single cell, has a very strong resistance to the external environment, the general commercial disinfectant basically can not kill the coccidia oocyst, so that the coccidiosis oocyst can be generally survived in the poultry production environment.
Oocysts are sporeized and reach the infectious stage within about 24 to 72 hours, with the main circulating coccidiosis species becoming infectious within 48 hours. Infectious oocysts have 4 sporangia, each containing 2 sporospores.
Fig.2 Spore-based Emeridium oocyst electron microscopy[4], each spore-defined coccidioidal oocyst contains 4 sporangia, while each sporangia contains 2 sporospores.
Life history of coccidiosis
A complete life cycle of coccidiosis includes both in vitro and in vivo stages, which generally take about 4 to 8 days, depending on different coccidiosis species and environmental conditions. Unlike bacterial or viral diseases, coccidiosis has a self-limiting character during its development. The life history of the tender Amy Coccidia can generally be used as a representative of all the life history of The Worms.
In the in vivo stage, mainly spore-like oocysts are ingested from the environment by chickens, the oocyst wall of coccidiosis is crushed under the action of physical digestion (milling) of the muscular stomach, releasing the sporozoites into the intestinal lumen, thus entering the epithelial cells of the small intestine and beginning to multiply. At least 2 asexual reproduction (also known as fission reproduction) and 1 sexual reproductive process are required to form zygotes, which mature into oocysts, which are released from the intestinal mucosa and excreted with feces.
The in vitro stage is the sporeization process of the coccidioid oocyst, and the sporeization of coccidiosis also requires certain conditions, including oxygen, temperature (above 20 °C) and humidity.
Fig.3 Life history of coccidiosis
Fig.4 In vivo reproduction of coccidiosis
Classification of coccidiosis
E. coccidioides can colonize and multiply in the digestive tracts of different species of animals and birds, and there are currently 9 known coccidiosis types in chickens, namely E. acervulina, E. brunettis, giant coccidiosis (E.maxima), tender coccidiosis (E.tenella), poisonous coccidiosis (E.necatrix), precocious coccidiosis (E. praecox), contaxative coccidiosis (E.mivatti), and bulbophyllum brachiostis (E.mitis) and E. hagani 5.
Different varieties of coccidiosis are characterized by host specificity and site specificity, so that the following biological features can be used to identify coccidiosis species:
The part of the intestine where lesions appear;
Characteristics of lesions;
Morphological characteristics of the oocyst;
The site of the worm body in the epithelial cells of the host intestine;
Shortest time for spore formation;
Minimum duration of incubation period;
The size of the schizoite and its location at the time of development;
Immunogenicity compared to standard strains5;
Table 1: Characteristics of the general lesions of nine coccidiosis (site of infection on the intestine, lesion characteristics), microscopic features (morphology, size, and sharp angle of the egg sac, fissur size, colonization site in intestinal tissue), and life cycle characteristics (minimum time required for in vivo reproduction, minimum time required for sporoporation) [5].
Biological characteristics of coccidiosis and the main infection of coccidiosis species on broilers
Why can coccidiosis infections become an inevitable and persistent threat to global poultry production? This is because coccidiosis has become a pervasive and highly evolutionarily successful parasite in its co-evolution with the red proto-chicken for thousands of years. The biological characteristics of coccidioides that are so "successful" are:
Parasites that are ubiquitous and highly evolved; short life cycles, only 4 to 8 days, and can complete the maximum amplification of the number at an exponential rate of reproduction; high tolerance to the external environment, which is basically impossible to remove from poultry production sites; coccidiosis vectors are very extensive; and today's intensive broiler production creates perfect conditions for coccidiosis infection and spread.
The species of coccidiosis infection in chickens is closely related to their feeding cycle and environment, and the longer the feeding time, the more species may be infected. Of course, the effects of different coccidiosis species on the pathogenicity and production of chickens are also different, and there are 4 main types of coccidiosis infections that are mainly concerned in broiler chickens, namely:
1. Eimeria Acervulina heap coccidiosis
Common and recognized as the species that causes indigestion and malabsorption;
Duodenal white dot or brush necrosis;
It mainly parasitizes the tip of the intestinal villi, and the necrosis site consists of a large number of dead intestinal cells, oocysts and immune cells;
The time of the greatest damage is the third generation of circulation, corresponding to broilers about 20-25 days old;
Higher challenges affect feed-to-meat ratio and intestinal health;
Photo by Elanco TC
2. Eimeria Maxima giant coccidiosis
Red needle-like bleeding spots on the intestinal wall, often seen with detachment of epithelial cells or increased secretion of intestinal mucus6;
Since it is mainly parasitic at the base of the intestinal villi, larger oocysts can destroy the intestinal villi when released, resulting in significant gastrointestinal malabsorption, impaired intestinal function, and predisposing to secondary Clostridium enteritis;
Chickens develop immunity quickly after infection, but not all chickens ingest the egg sac evenly, so late infection is also common and at risk throughout the white-feathered broiler feeding period;
The largest species of oocyst individuals, parasitic in the deep tissues of the intestine, causing focal bleeding, which manifests as red needle-like bleeding spots in the serous layer (lateral side of the intestine);
The parasitic site of Giant Coccidiosis and the degree of damage to intestinal villi make its impact on the ratio of feed to meat and intestinal health very significant;
3. Eimeria Tenella tender coccidiosis
Hemorrhagic type of the species, where significant bleeding spots may be seen in the cecum;
The peak of infection is usually late, at the age of 28-32 days;
Affecting the cecum but surviving chickens have a limited impact on production capacity, and the outbreak mainly causes the death of chickens and leads to losses;
4. Eimeria Necatrix poisons coccidiosis
The site of injury is similar to that of giant, mainly in the middle of the intestine; due to its asexual reproduction stage, it forms a huge fissile body and parasitizes the base of villi, which is very serious for intestinal villi damage. Although the site of injury is in the small intestine, the formation of the oocyst is in the cecum.
Symptoms are typical of salt and pepper lesions (red/reddish-brown-white), very susceptible to necrotizing enteritis caused by Clostridium, leading to severe flatulence in the intestine;
Even moderate infection can lead to severe weight loss and death;
This species appears to have difficulty competing with other coccidioides (placeholder) rarely occurs in white-feathered broilers with shorter rearing periods, with peak infections greater than 8 weeks of age.
epilogue
Coccidiosis is a parasitic disease, and even subclinical coccidiosis problems can have a significant impact on flock production performance. Coccidiosis cannot be completely eliminated, but can be managed well, because coccidiosis infection is closely related to many external factors, including other factors of enteritis, so a systematic solution is needed, and similarly, after the prohibition of antibiotics, in addition to seeking some possible alternatives, it is also necessary to transform thinking and pay attention to all the factors affecting the health of the intestine, especially the problem of coccidiosis infection, which is very susceptible to secondary Clostridium enteritis.