What is fluke infection?
Fluke infections, also known as trematode infections, are caused by parasitic flatworms belonging to the class Trematoda. These parasites, commonly referred to as flukes, can infect humans and a wide range of animals, including mammals, birds, and fish. Fluke infections are prevalent in tropical and subtropical regions, where they can cause significant morbidity and mortality, particularly in areas with poor sanitation and limited access to healthcare.
There are several species of flukes that can infect humans, each with its own life cycle, host specificity, and clinical manifestations. The most common types of fluke infections in humans include:
- Liver Fluke Infections: Liver flukes belong to the genus Fasciola and include species such as Fasciola hepatica and Fasciola gigantica. These parasites primarily infect the liver and bile ducts of humans and animals. Infection occurs through ingestion of contaminated water or aquatic plants containing infective larvae (cercariae). Liver fluke infection can cause hepatobiliary disease, including cholangitis, cholecystitis, and obstructive jaundice.
- Intestinal Fluke Infections: Intestinal flukes infect the gastrointestinal tract of humans and animals. Common intestinal flukes include species of the genus Fasciolopsis, such as Fasciolopsis buski. Infection occurs through ingestion of contaminated water or aquatic plants containing infective metacercariae. Intestinal fluke infection can cause gastrointestinal symptoms such as abdominal pain, diarrhea, and malabsorption.
- Lung Fluke Infections: Lung flukes infect the respiratory tract of humans and animals. Common lung flukes include species of the genus Paragonimus, such as Paragonimus westermani. Infection occurs through ingestion of raw or undercooked freshwater crustaceans (e.g., crabs, crayfish) containing infective metacercariae. Lung fluke infection can cause pulmonary symptoms such as cough, chest pain, hemoptysis (coughing up blood), and respiratory distress.
- Blood Fluke Infections: Blood flukes belong to the genus Schistosoma and include species such as Schistosoma mansoni, Schistosoma japonicum, and Schistosoma haematobium. These parasites infect the blood vessels of the intestine or urinary tract, depending on the species. Infection occurs through skin contact with water containing infective cercariae. Blood fluke infection can cause schistosomiasis, a chronic inflammatory disease characterized by abdominal pain, diarrhea, hematuria (blood in urine), and hepatosplenomegaly (enlargement of the liver and spleen).
What is the relationship between fluke infection and oxidative stress?
The relationship between fluke infections and oxidative stress involves complex interactions between the host immune response, parasite-induced inflammation, and oxidative stress pathways. Fluke infections, caused by parasitic flatworms belonging to the class Trematoda, can elicit a range of host immune responses and inflammatory reactions, which in turn can lead to the generation of reactive oxygen species (ROS) and oxidative stress. Several mechanisms contribute to the relationship between fluke infections and oxidative stress:
- Host Immune Response: When fluke parasites infect the host, the host’s immune system responds by activating various immune cells and inflammatory mediators to combat the infection. Immune cells such as macrophages, neutrophils, and eosinophils produce ROS as part of their antimicrobial defense mechanisms to eliminate the parasites. However, excessive ROS production can lead to oxidative stress and tissue damage in the host.
- Inflammatory Reactions: Fluke infections often induce inflammatory reactions in the host tissues as a result of parasite migration, tissue damage, and host immune responses. Inflammation is associated with the production of pro-inflammatory cytokines, chemokines, and reactive oxygen species (ROS) by immune cells. Chronic inflammation can exacerbate oxidative stress and contribute to tissue injury and fibrosis in the affected organs.
- Parasite-induced Damage: Fluke parasites can directly induce oxidative stress and tissue damage through various mechanisms. For example, adult flukes may release excretory-secretory products (ESPs) or metabolites that contain molecules capable of generating ROS and damaging host tissues. Additionally, parasite eggs or larvae may provoke inflammatory responses and oxidative stress in host tissues during migration or when they become trapped in tissues.
- Host Defense Mechanisms: The host attempts to counteract oxidative stress and protect against tissue damage through antioxidant defense mechanisms. Antioxidant enzymes such as superoxide dismutase (SOD), catalase, and glutathione peroxidase scavenge ROS and mitigate oxidative damage. However, in chronic or severe infections, the host’s antioxidant defenses may become overwhelmed, leading to oxidative stress and tissue injury.
- Role in Pathogenesis: Oxidative stress induced by fluke infections can contribute to the pathogenesis of various disease manifestations associated with these infections. For example, oxidative stress has been implicated in the development of liver fibrosis and hepatocellular injury in liver fluke infections (e.g., Fasciola hepatica, Fasciola gigantica), as well as in the pathogenesis of bladder cancer associated with Schistosoma haematobium
Overall, the relationship between fluke infections and oxidative stress involves a complex interplay between host immune responses, parasite-induced inflammation, and tissue damage.