Disease Vectors and Pathogens

Entamoeba histolytica is an anaerobic parasitic protozoan, predominantly infecting humans and other primates. E. histolytica may modulate the virulence of certain human viruses and is itself a host for its own viruses. For example, AIDS accentuates the damage and pathogenicity of E. histolytica. 

Fertilization of the female gamete by the male gamete occurs rapidly after gametogenesis. The fertilization event produces a zygote. The zygote then develops into an ookinete. The zygote and ookinete are the only diploid stages of P. falciparum.

Dientamoeba fragilis is a single-celled parasite found in the gastrointestinal tract of humans, pigs and gorillas. It is an important cause of travellers diarrhoea, chronic diarrhoea, fatigue and, in children, failure to thrive.

Plasmodium vivax (malaria parasite) completes its asexual part of life cycle in people and the sexual part in the female Anopheles mosquito (Digenetic life cycle). Trypanosam cruzi possesses a digenetic life cycle, involving a hematophagous insect vector and a mammalian host.

Duration of exoerythrocytic cyle is 8 days in Plasmodium vivax, while it is 14-15 days in Plasmodium malariae. Incubation period is 12-14 days Plasmodium vivax, while it is 20-24 days in Plasmodium malariae.

Parasites like Trichinella frequently increase the IgE levels, usually polyclonally. This tends to inhibit the protective effect of IgE by diluting out the specific IgE on the mast cell. Inflammation induced by mast cell degranulation leads to influx of IgG, which causes damage to the parasite.

Malarial fever occurs when the malaria parasites (Plasmodium) rupture red blood cells, releasing toxins and debris into the bloodstream. This rupture triggers the immune system and causes the characteristic fever spikes. The initial mosquito bite merely transmits the parasites, while fever begins later during the blood-stage infection cycle.

Aedes aegypti is the primary mosquito vector responsible for transmitting dengue fever. Unlike Anopheles mosquitoes that transmit malaria, Aedes aegypti is a day-biting mosquito found in tropical and subtropical regions. Plasmodium refers to the malaria parasite, while male Anopheles mosquitoes do not bite humans.

All of the above viral diseases are transmitted by mosquitoes.

4

Leishmaniasis is caused by Leishmania donovani and is transmitted by sand flies. Leishmaniasis has a wide distribution that extends from the Mediterranean to Middle Asia, to southern Russia and China. It is also known as Kala-azar (black fever) or Assam fever.

Balantidaisis is a form of dysentry. It is caused by the only ciliated protozoan parasite of humans (Balantidium coli). This parasite is found worldwide. There is a slight correlation between the incidence of the disease and the presence of hogs. The balantidaisis organisms feed on epithelium and red blood cells in the colon and can cause ulcers.

Trich is a sexually transmitted disease, and is caused by the single-celled protozoan parasite, Trichomonas vaginalis, producing mechanical stress on host cells and then ingesting cell fragments after cell death. It is primarily an infection of the urogenital tract. The most common site of infection is the urethra and the vagina in women.

Trichomonas vaginalis, a protozoa, causes (the usually sexually transmitted) trichomoniasis. Although asymptomatic most of the times, it needs attention as it is known to facilitate HIV transmission. Symptoms include vaginitis leading to white discharge in women and urethritis leading to burning micturition in men.

Babesiosis is caused by the Babesia parasite, which is carried by ticks. This disease can also be spread through blood transfusions if a donor has a Babesia infection that has not been diagnosed.