The Mastigophora’s group of protozoan parasites are commonly known as flagellates because they have one or more flagella (exactly like spermatozoa) to propel themselves in their environment. Here are the most prevalent flagellates protozoan parasites.
Trichomonas vaginalis caused a disease called trichomoniasis and is considered as the most common protozoan parasite infecting humans in developed countries. This parasite has a quite unusual life cycle as it is strictly sexually transmitted between humans, its only known host. It is present worldwide and, of course, risk factors for this disease include having multiple sexual partners and/or other sexually transmitted diseases. According to the World Health Organization, it is the most frequent curable sexually transmitted disease with more than 170 million new cases per year. This infection is often asymptomatic for men, but symptoms associated with urethritis can occur. The fact that men are mostly asymptomatic contributes to the propagation of this disease, as they can transmit the disease without being aware of having it. Vaginitis and other genital symptoms are frequent for women. Diagnosis can be made by direct visualisation of the parasite in vaginal or urethral secretion under the microscope. However, this method is not considered as sensitive and antibody detection or parasite culture are also often used. Finally, this infection is easily treatable with a single dose of anti-parasitic drug. However, reinfections are frequent and it is very important that all the sexual partners were treated and that sexual activities were avoided until all symptoms are gone.
The intestinal parasite Giardia caused a disease called giardiasis. It is present worldwide, but it is more prevalent in warmer countries. The transmission of this parasite occurs through the ingestion of cysts present in contaminated food or water, as well as by putting contaminated hands in the mouth. Children are then more at risk to acquire this parasite than adult. Many wild animals can be intermediate hosts for this parasite and contribute to its persistence in the environment. Infection with Giardia can remain asymptomatic, but can also provoke gastrointestinal symptoms. Diagnosis is performed by detection of cysts in the faeces using a microscope, but they are usually difficult to detect, causing a delay in the diagnosis. Furthermore, a fluorescent test is now available to detect the presence of specific antibodies directly in the faeces. Effective treatments are available for severe cases, but not always necessary as this disease usually resolve by itself.
There are more than 20 species of the parasite Leishmania able to infect humans in tropical and subtropical countries. These parasites are transmitted by the bites of certain sandflies species and are estimated to affect more than 12 million people worldwide, but it is thought to be an underestimation of the real number. They cause different symptoms depending on the species involved. There are three main forms of the disease called leishmaniasis: a cutaneous form represented by a single skin ulcer, a mucocutaneous form including the progressive destruction of the nose and mouth, and an always fatal if untreated visceral form infecting internal organs. Leishmaniasis is also a common co-infection with HIV in some areas, such as Southern Europe. Diagnostic methods include parasite visualisation under the microscope and parasite’s genetic materials (DNA or RNA) amplification. There are a number of anti-parasitic treatments available against Leishmania. However, resistance to treatment and toxicity are problematic.
Trypanosoma species are responsible for two diseases in human: African trypanosomiasis or sleeping sickness transmitted by the bite of tsetse flies in Africa and Chagas disease transmitted by contact with the faeces of the kissing bugs in Latin America. The African sleeping sickness is estimated to affect 20 000 people. It present an initial chancre at the inoculation site followed by fever and a subsequent central nervous system invasion leading to somnolence, headaches and neurological symptoms. Most of the time, the neurological symptoms occur months or years after the initial infection. Diagnosis of the African sleeping sickness is made by the parasite’s visualisation using microscope in biological specimens, such as blood, chancre fluid, lymph node aspiration, bone marrow or cerebrospinal fluid. Anti-parasitic treatments are complex but effective against the parasite responsible for the African sleeping sickness, especially in the early stage of the disease. Unfortunately, death caused by the treatment can occur in up to 5% of the cases in the neurological stage of the disease type present in East Africa representing 2% of the total number of cases. However, both type of the diseases are almost always fatal when left untreated.
Chagas disease is thought to infect between 6 and 7 million people. As contact with the faeces of the kissing bugs transmit it, it could be transmitted by the ingestion of contaminated food. Furthermore, cases of transmission by the mother to the unborn child during pregnancy, and by blood transfusion or organ transplant have also been reported. Early Chagas disease’s infection includes mild symptoms followed by a chronic asymptomatic phase. Other more severe symptoms, including cardiomyopathy and digestive tract disorders, appear up to many years after the initial infection. These symptoms can ultimately results in death. Diagnosis of Chagas disease is usually made by detection of antibodies in the blood specimens. Anti-parasitic treatments are effective in the early stage of the infection, but are less or not effective in the chronic phase. As such, treatments in the chronic phase are more related to the management of the symptoms rather than the curing of the disease.
Sources: Centers for Disease Control and Prevention, World Health Organization
