Trypanosomiasis in Fish

Trypanosomiasis in fish is caused by a single-celled parasitic organism called Trypanosoma. This disease can affect various animals, including fish. Fish trypanosomes are found in both freshwater and marine environments, and they can infect many different species of fish.

Trypanosoma species are transmitted to fish through the bite of infected insects, such as mosquitoes or black flies, which act as vectors.

Once inside the fish’s bloodstream, the parasites can cause a range of symptoms, including anemia, lethargy, reduced growth rate, and even death in severe cases.

The introduction of trypanosomiasis into a fish population can have significant economic and ecological impacts. Infected fish may have reduced productivity, leading to losses for aquaculture operations.

Additionally, infected fish may act as a reservoir for the parasites, allowing them to spread to other fish populations in the area.

Trypanosoma in fish

Morphological characteristics

  • The body length of Trypanosoma are short (mean 22.3 μm, range 17.6-25.9 μm)
  • They have narrow body width (mean1.7 μm, range 1.3-2.0 μm)
  • Central nucleus presents
  • Their membrane is not well developed, narrow and undulating
  • Relatively long free flagellum (mean 10.1 μm, range 7.4-13.3 μm).
  • Kinoplast is oval shaped and situated at approximately one quarter of body length from posterior end of the body.

Life cycle

Trypanosomes are a group of parasitic protozoan parasites that can infect a wide range of vertebrate hosts, including fish. The life cycle of Trypanosoma in fish can vary depending on the species of the parasite and the type of fish host.

In general, the life cycle of Trypanosoma in fish can be described as follows:

Infection: Trypanosomes infect fish through the bite of infected invertebrate vectors, such as leeches, insects, or crustaceans. The parasites can also enter the fish through wounds or abrasions in the skin.

Bloodstream invasion: Once inside the fish, the trypanosomes multiply and invade the bloodstream, where they can be transported to different organs and tissues.

Replication and transmission: The trypanosomes continue to replicate and divide in the fish’s bloodstream and other tissues. Some species of trypanosomes can also infect the fish’s nervous system. When an infected fish is eaten by a predator, the parasites can be transmitted to the predator.

Vector transmission: Some species of trypanosomes in fish are transmitted to new hosts through the bite of an infected vector. The parasites can infect the vector during a blood meal and then be transmitted to a new fish host during the vector’s next blood meal.

Shedding: Infected fish can shed trypanosomes in their feces, which can contaminate water sources and infect other fish.

The life cycle of Trypanosoma in fish can vary depending on the species of the parasite and the type of fish host. Some species of trypanosomes can also infect other hosts, such as mammals or birds. Understanding the life cycle of these parasites is important for developing effective control measures and preventing the spread of infection.

Geographical distribution of Trypanosoma

The distribution of Trypanosoma varies depending on the species.

African trypanosomiasis is caused by Trypanosoma brucei and is found in sub-Saharan Africa, particularly in rural areas where people are in close contact with tsetse flies, which are the vectors that transmit the parasites.

The disease is endemic in 36 countries in sub-Saharan Africa, with an estimated 60 million people at risk of infection.

Chagas disease is caused by Trypanosoma cruzi and is found mainly in Latin America, particularly in rural areas of Mexico, Central America, and South America.

It is estimated that between 6 and 7 million people are infected with Chagas disease, with most cases occurring in Bolivia, Colombia, and Peru.

Other species of Trypanosoma are found in various regions of the world. For example, Trypanosoma congolense and Trypanosoma vivax are found in sub-Saharan Africa, while Trypanosoma evansi is found in Asia, Africa, and South America. Trypanosoma rangeli is found in Central and South America, and is not known to cause disease in humans.

In summary, the geographical distribution of Trypanosoma varies depending on the species, but generally, they are found in tropical and subtropical regions of the world.

Fish species affected by Trypanosoma

Some fish species that have been known to be affected by Trypanosoma include:

Tilapia: Tilapia is a popular fish species in aquaculture that has been shown to be susceptible to Trypanosoma infections. Trypanosoma congolense, Trypanosoma brucei, and Trypanosoma vivax are some of the species that have been identified in tilapia.

Catfish: Several species of catfish, including Clarias gariepinus and Heterobranchus longifilis, have been reported to be infected with Trypanosoma. These infections can cause reduced growth and mortality in catfish populations.

Salmon: Trypanosoma is a common cause of mortality in Atlantic salmon farming. The parasite can cause anemia and lead to reduced growth and productivity in infected fish.

Trout: Several species of trout, including rainbow trout and brown trout, have been found to be infected with Trypanosoma. These infections can cause a variety of symptoms, including anemia, lethargy, and reduced growth.

Piranha: Some species of piranha have been found to be infected with Trypanosoma. Infections can lead to reduced appetite and mortality in piranha populations.

Causing sign and symptoms

Trypanosoma is affected by both marine and freshwater fishes..

  • Key blood metrics and expression of genes changes
  • Total number of circulating RBCs may decrease
  • T. carassii may directly or indirectly suppress host erythropoiesis.
  • The infected fish may have loss of appetite
  • Lethargy
  • Emaciation
  • Severe anemia
  • Splenomegaly
  • Rise of parasitaemia in the blood
  • Foamy macrophages are also noticed

Diagnosis of Trypanosoma

Fish trypanosomes diagnosis can be made through gill biopsy, skin cytology, fecal examination, or necropsy.

Microscopic examination: The most common method for diagnosing fish trypanosomiasis is microscopic examination of blood or tissue samples.

A drop of blood or tissue fluid is placed on a microscope slide, stained, and examined under a microscope. The presence of Trypanosoma spp. In the blood or tissue fluid confirms the diagnosis.

Polymerase chain reaction (PCR): PCR is a sensitive and specific method for detecting Trypanosoma spp. DNA in blood or tissue samples. This method involves amplifying specific regions of the parasite’s DNA using primers and a DNA polymerase enzyme. The amplified DNA is then detected using gel electrophoresis or other methods.

Serological tests: Serological tests, such as enzyme-linked immunosorbent assay (ELISA), detect antibodies against Trypanosoma spp. In the blood of infected fish. However, these tests are less sensitive than microscopic examination or PCR.

Histopathology: Histopathology involves examining tissue samples under a microscope to detect changes caused by the parasite. This method is useful for detecting chronic infections or evaluating the severity of the disease.

It is important to note that fish trypanosomiasis can be easily misdiagnosed or overlooked, as the symptoms can be non-specific or absent. Therefore, it is important to use multiple diagnostic methods and consult with a veterinarian or fish health specialist for proper diagnosis and treatment.

Treatment of Trypanosoma

Treatment of Trypanosomiasis can be done by using several compound, they are-
1)Benznidazol I/M (5 mg kg–1 b.wt.)
3)Pentacarinat injection.
4)amprolium, bithionol and toltrazuril.
5)infected fish can be treated with 3% common salt for 10 minute or 1: 2500 formalin solution.
6)23 C temperature in recirculating UV-treated tap water used for fish clean.
7)nifurtimox and benznidazole.
8)Response to PHZ treatment


Prevention method of Trypanosomiasis are described below-

An antimicrobial peptide such as Hepcidin and an regulatory protein ( iron) that prevents the release of excessive iron in blood.
A tightly regulated innate immune response.
IgM purified from serum recovered.
Regular control of health conditions and preventive treatment of fish.
Prevent the water environment from deteriorating.
To boost resistance of fish under culture
Reduce pathogens in the water body.
Monitoring fish diseases.


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