Trypanosoma cruzi

Trypanosoma cruzi is a species of parasitic kinetoplastid. This tiny organism is the cause of Chagas disease. It belongs to a group of single-celled organisms called protozoa. These parasites are known for boring into the tissues of other organisms. They primarily feed on blood and sometimes on lymph. This behavior can cause various illnesses in different animals. In humans, it leads to Chagas disease. In horses, it causes dourine and surra. Cattle may develop a disease similar to brucellosis.

The parasite relies on a host and a specific insect to spread. This insect is called a triatomine bug. People also call it an assassin bug, a cone-nose bug, or a kissing bug. These bugs often live in the nests of vertebrate animals. They bite these animals to consume blood for food. If a bug is infected, it transmits the parasite through its feces. The bug deposits waste on the host's skin while feeding. The parasite then enters the body through the bite wound or by being scratched into the skin.

There are different ways the parasite moves through its life cycle. The cycle begins in an animal reservoir, such as a mammal. A triatomine bug, like Triatoma infestans, acts as the vector. When the bug takes a blood meal, it ingests the parasite. Inside the bug, the parasite enters the epimastigote stage. This is an elongated, flagellated form that reproduces through binary fission. The epimastigotes then move to the rectal cell wall. There, they become metacyclic trypomastigotes, which are the infectious, non-dividing forms.

Infection can also happen through oral ingestion. This occurs if food is contaminated with the feces of an infected bug. Once inside a host, the metacyclic trypomastigotes use a flagellum to swim. A flagellum is a tail-like structure used for movement. These parasites must invade host cells to survive. They use macromolecules like laminin, thrombospondin, heparin sulphate, and fibronectin to stick to the host. They must also cross a network of proteins on the cell exterior. Once inside, they transform into amastigotes.

Amastigotes are rounded, intracellular forms with a short flagellum. They multiply within the host's cytoplasm using binary fission. After several rounds of replication, they differentiate into bloodstream trypomastigotes. When the host cell ruptures, these parasites are released into the blood. They can then infect new cells or be picked up by another triatomine bug. The name "cruzi" honors the Brazilian scientist Oswaldo Cruz. He was the teacher of Carlos Chagas, the man who discovered the parasite.

Chagas disease can affect the body in different ways over time. The acute form often goes unnoticed, though it might cause swelling at the entry site. As the infection progresses, the number of amastigotes per infected cell (APC) increases. The chronic form can develop 30 to 40 years after the initial infection. This stage can damage internal organs like the heart, esophagus, and colon. It can also affect the peripheral nervous system. Severe heart lesions or heart failure can lead to death.

Damage to the heart is a major concern in chronic cases. The infection causes an inflammatory response followed by cellular damage. The body then attempts to recover through a process called fibrosis, which is the formation of scar tissue. Patients may also suffer from thromboembolic syndrome. This involves thrombosis, where a blood clot forms, and embolism, where the clot travels to block a vessel. These clots can affect the brain, spleen, and kidneys. This can lead to arrhythmias or sudden death due to cardiac failure.

Research shows how the parasite interacts with the body's systems. In mice, chronic infection is linked to the activation of certain proteins like ERK and NF-κB. The parasite also induces the host to overproduce 2-series prostaglandins. These chemicals are immunosuppressive, which helps the parasite evade the immune system. While acute cases can be treated with nifurtimox and benznidazole, no effective therapy exists for chronic cases. Understanding these biological mechanisms is vital for managing the disease globally.