Coccidiosis in fish. Lifecycle of coccidiosis, development, pathogenesis and medications

Table of contents

1. Introduction

2. Taxonomy...

3. Coccidiosis in fish..

4. Life cycle

5. Transmission.

6. Pathogenesis.

7. Prevention and treatment..

8. Conclusion

9. References

Abstract

Coccidiosis is a disease which is cause by protozoan parasites of the apicomplexan genus Eimeria and is transmitted via ingestion of infective oocysts . It affects many vertebrates and invertebrates causing mortality, poor performance of animals and reduce productivity. This disease mostly affect poultry sector but its different species are also present in fish and causes economic loss. Coccidiosis in fish has been study extensively as it is regarded as a chronic and its impact are easily overlooked. There are at least 18 genera under 3 families of order Eucoccidiorida that are responsible to cause some form of coccidiosis in different animals including mammals, avians as well as piscines. About 250 species of coccidiosis are known to occur in fish and among them Eimeria and Goussia spp are the most prevalence one. Taxonomic classification has been a difficult task and is determined on the basis of morphological features of oocysts. Coccidiosis generally have 3 stage in their lifecycle with some variation according to species. About 30% of coocidia develops extraintestinally and most of the fish coccidia are kept undera Eimera genera. Transmission occur via direct as well as by indirect method but direct method id more common and simple. Coccidiosis can cause mild to serve damage and pathogenesis can be differ with species. For prevention and control, different anticoccidial drugs are used. However, sanitation is prime factors to reduce the risk of oocysts introduction in animal. The present review has summarize the status of fish coccidia and has provide an insight about the life cycle, taxonomy, transmission, pathogenesis, prevention and treatment.

List of tables

1 Common and/or pathogenic coccidian infections of fish

2 Anticoccidial agents use for the treatment of coccidiosis

List of figures

1 Classification of coccidiosis

2 Schematic diagram of life cycle of Eimeria. Source:

3 Structure of sporulated Eimeria oocysts

4 Typical oocysts of Eimeriid

5 Infection of Eimeria funduli

1. Introduction

Coccidiosis is a disease which is cause by protozoan parasites of the apicomplexan genus Eimeria and is transmitted via ingestion of infective oocysts . It affects many vertebrates and invertebrates causing mortality, poor performance of animals and reduce productivity (Chapman, et al., 2013). It has greater impact in poultry sector and considered as one of the most economically important disease. Use of anticoccidial feed additives as a prophylactic measure in the broiler industry has been major means of controlling it and has played significant role for the growth of this sector (Allen & Fetterer, 2020). Once infected with this disease, it seriously affects the growth and feed utilization of chicken and it has causes loss of around $1.5 billion annually to US poultry industry (Yun, Lillehoj, & Lillehoj, 2002). More studies are focus on the mammalian and avian coccidiosis than that on fish coccidia, which may be because of commercial value. In case of animal husbandry, intensive farming practice could lead to development of infective oocyst on pasture or litter. In recent period, work on fish coccidia has been descriptive, based on oocyst appearance, and for most species only this stage and the site of infection are known. However, impact of coocidiosis on fish disease has been realized, together with expansion in aquaculture, has helped to widen the knowledge of this group (Davies & Ball, 1993).

Not only the poultry sector has been facing the problem of coccidiosis, numbers of coccidia exists in fishes from difference source of water such as freshwater streams, rivers, lakes, brackish water, and ocean. The coccidia include the genera Eimeria, Isospora, Hammondia, Toxoplasma, Besnoitia, Sarcocystis, and Frenkelia (Fayer, 1980). Numbers of teleosts and several elasmobranchs each contain one or more kinds of coccidia and host specificity is low due to which fish share these parasites. Fishes infected with this diseases have been found in all continents of the world except Antarctica, although records from some areas (e.g. Africa, Australia, Indian subcontinent, New Zealand and South America) are less than from others (e.g. Canada, China, Europe, North America and Russia) (Davies & Ball, 1993). The species Eimeria are more prevalence than others in cultured fresh water fish (Rayamajhi & Shrestha, 2011).

Coccidiosis is caused by a wide range of coccidian parasites. The coccidian parasites are spore forming obligate intracellular protozoan parasites There are at least 18 genera under 3 families of order Eucoccidiorida that are responsible to cause some form of coccidiosis in different animals including mammals, avians as well as piscines (Ettinger & Feldman, 1995). Eimeria spp. possess a complex life cycle which have both sexual and asexual stage and are host as well as infection-site specific. Birds of different genetic background shows different kind of pathogenicity. Hence, in the natural host, the immunity is specific to species, chickens being immune to one species of Eimeria are susceptible to others (Dalloul & Lillehoj, 2006). The parasite have an oral-faecel lifecycle which has 3 phases: schizogony (also known as merogony), gametogony and sporogony (or sporulation). Oocyst is the infective transmission stage which contain sporozoites, that is released and penetrates the epithelial cells of intestine. In poultry, lifecycle completes in about 7 days whereas it may take longer time in case of ruminants. The level of destruction by this disease depends on the number of infective oocysts ingested, which is depends upon to what extent the sporulation has formed. Ideal conditions required for the development is warmth, oxygen and moisture, which is all present in commercial livestock prodction (Chapman, et al., 2013). So, a number of species of Eimeria is known to cause coccidiosis in poultry (mainly chickens) as well as pisciculture species. Here main focus will be on coccidiosis of fish.

In order to reduce the incidence of coccidiosis spread, good management practice along with hygiene will work but for absolute cure prophylactic medication and vaccination is needed (Dalloul & Lillehoj, 2006). Anticoccidial drugs which targets the specific stage of its life cycle is needed to prevent this disease such as sulfonamides, ionophores and toltrazuril (McDonald & Shirley, 2009).

2. Taxonomy

Fish coccidia were found and described 110 years ago. Number of coccidian species affecting fish has been changed and till the date about 250 coccidia species has been record in fish. Coccidia of one family Eimeriidae and two genera Eimeria and Goussia has been found in Elasmobranchii, whereas coccidia of three families (Calyptosporidae, Cryptosporidiidae, Eimeriidae) and eight genera ( Calyptospora, Cryptosporidium, Crystallospora, Eimeria, Epieimeria, Goussia, Isospora, Octosporella) has been seen in Actinopterygii (Belova & Krylov, 2000). Some authors consider only Eimeridiidae and Sarcocystidae as family of order Eucoccidiorida (Levine & Ivens, 1981). Although number of species from these different genera causes coccidiosis in different animals, here the focus will be given to Eimeria, since it is the most prevalent coccidian in case of fishes. The Eimeria spp. is capable of causing disease coccidiosis in cattle, poultry, dogs, cat, smaller ruminant sheep and goat (Chartier & Paraud, 2012). The classification of coccidians is shown in figure 1 (Levine & Ivens, 1981)

Abbildung in dieser Leseprobe nicht enthalten

Fig 1: Classification of coccidiosis

Identification of Emeria species has been a difficult task due to its complexity. In 1984, Long and Joyner pointed out the difficulties of identifying Eimeria species. Additionally, they mentioned about the limitation of using morphological characters of oocyst for identification purpose and suggested for using other characteristics as identification method (Davies & Ball, 1993; Tenter, et al., 2002). Although, the information of oocysts and its structure provides an important feature to differentiate genera and species of coccida in fishes. For instance, Upton et al. (1984) use oocysts and sporocyst characteristics for identification of the Eimeriidae in North American Fish. Fish coccidia generally contain oocysts which have 4 sporocysts and each of it contain 2 sporozoites (tetrasporocystic, dizoic), which confirm them into genus Eimeria (Davies & Ball, 1993).

The Eimeria lie within the family Eimeriidae and it accounts 75% of the species within this family. And it is the most studied under the genera Apicomplexa with 1,700 described species (Ogedengbe, Ogedengbe, Hafeez, & Barta, 2015). Classification of eimeriid coccidian is mainly done on the basis of morphological and life cycle details (Levine N. D., 1998). But, in modern time, its classification is carried out on the basis of rDNA and mitochondrial genes, which indicate Eimeria may be paraphyletic to Isopora and Cyclospora (Morrison , et al., 2004). According to Levine (1988), fish coccidia as a group include family Eimeriidae Minchin, 1903, along haemogregarines and dactylosomes. Historically however, the term “coccidia” has referred mainly to obligate intracellular protozoa of the genera Eimeria and Isospora in the family Eimeriidae. There are many Eimeria species in fish but few Isospora, and there are parasites from three additional families (Davies & Ball, 1993).

Classification scheme for fish coccidia based on Levine (1982, 1983, 1988)

Phylum APICOMPLEXA Levine, 1970

Apical complex, presence of polar rings, rhoptries, micronemes, conoid, and consist of subpecullier microtubules at some stage; micropore(s) generally present at some stage; sexuality by syngamy; all species parasitic.

Class Sporozoasida Leuckart, 1879

Presence of conoid forming complete cone shape, reproduction by both sexual and asexual (mostly), oocysts having infective sporozoites, locomotion via body flexion, gliding, undulation or flagella; flagella if present than found on microgametes only, homoxenous or heteroxenous.

Order Eucoccidiorida Leger and Duboscq, 1910

Merogony, gamogony, and sporogony present; in invertebrates and vertebrates

Family Cryptosporidiidae leger, 1911

Develop beneath the surface membrane of host cell or on its border , developmental stage give rise to attachment organ which help to anchor parasite to the base of parasitophorous vacuole, flagella is absent in microgamete, homoxenous, oocyst may or may not contain sporocycts, with 4 naked sporozoites.

Family Eimeriidae Minchin, 1903

Develop inside host cell, without attachment organelle or vaginal tube, Oocysts contains 0,1,2,4 or more sporocysts, each with 1 or more sporozoites; sporocycts are univalved, donot have dehiscence line, homoxenous, merogony and gamogony within host, sporogony usaully located outside, presence of 2 or 3 flagella in microgametes, in vertebrates or invertebrates.

3. Coccidiosis in fish

The common coccidians causing disease are Eimeria, Isospora, Cryptosporidium, Toxoplasma, Sarcocystis, Besnoitia and Frenkelia. Some of these may need two hosts to complete the life cycle while most of them need single host (Levine & Ivens, 1981). The coccidia are usually host specific, one species which infect one host is generally non-infective to other vertebrate host. Some host harbour more than one parasite, for instance: swine are infected by both Eimeria and Isopora species (Barta, 2001).

All the fish coccodia has been kept under the genus Eimeria, although they do not completely fit with the characters and life cycle pattern of this genus (Dykova & Lom, 1981). Over 200 species of eimeriids have been identified from different species of fish, and their occurrence has been underestimated. Mostly they are not common in fish but have affected certain species severely such as common carp. Piscine coccidia is less species specific than mammalian coccidia and often spread within same genus (Noga, 2010). Coccidiosis in fish is mainly caused by different species of Eimeria, with some reports of Cryptosporidium infections (Paperna, 1996; Landsberg & Paperna, 1986) as well as Goussia spp. (Davies & Ball, 1993; Molnar & Rohde, 1988). Fishes of different species including the elasmobranchs as well as teleosts have been found to be affected by this parasite (Dykova & Lom, 1981) and both wild as well as cultured species are found to be affected (Klinger & Floyd, 2016). Different freshwater fish species such as common carp, channel catfish, Nile tilapia, silver carp, masu salmon, Glossogoobius giuris, and Notopterus notopterus are mostly affected by coccidia .

In case of Nepal, in recent times rainbow trout farmers doing semi intensive farming system have been facing problems of poor growth and low yield due to coccidiosis ( Eimeria aurati) (Rayamajhi, Pradhan, & Roy, 2011). A number of Eimeria species along with others have been recorded from different fish species causing coccidiosis. Coccidia main site for development in other groups of vertebrate is gut but in case of fish their development occurs in extra intestinal also. About 30% of coocidia develops extraintestinally which differs fish from hoeotherms. Moreover, due to coccidia in fish, tissue specificity develops because of which same stages may develop in different part of organs and tissue within a single host (Davies & Ball, 1993). Common carp and goldfish is mostly affected by gut dwelling coccidian species Goussia carpelli. In case of carp hatcheries this parasite affects all age groups of fish but fry stage is the most affected one. The incidence of this parasite is usually high during July- September, at this time about 80-100% of carp were infected (Steinhagen & Hespe, 1998). In Nepal, coccidiosis has affected rainbow trout production and study has found that large size trout were severely affected with 50.1- 70.1% of prevalence rate (Rayamajhi, Pradhan, & Roy, 2011)

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