Parasites are the cause for some of the most troublesome diseases recognized by humans on the planet. Malaria alone affects hundreds of millions of people in third world countries every year, causing millions of deaths, while other parasites cause diseases that cost millions of more lives...

From Sleeping sickness to River Blindness to Elephantiasis, the list is longer than many imagine. This page gives rough introductions and descriptions for some of the most infamous of them...

Malaria

The undisputed king of parasite-caused diseases, Malaria is a serious human disease that weakens an infected individual and may easily lead to death. It is caused by the Sporozoan species known as Plasmodium. (Sporozoans are members of the parasitic Phylum Sporozoa (spohr-oh-ZOH-uh), one of several sub-groups of eukaryotic organisms in the (biological) kingdom Protista). Plasmodium is carried by the Anopheles (uh-NAHF-uh-leez) mosquito.

When an infected mosquito bites a human, some of its saliva, which contains spores of the parasite, is injected into the bloodstream. Once inside the body, Plasmodium infects liver cells and then red blood cells. Plasmodium grows rapidly within the infected cells and eventually causes these cells to burst at intervals of 48 or 72 hours. When millions of parasite-filled red blood cells burst, they dump large amounts of toxins into the bloodstream. The toxins produce chills and fever- the symptoms of malaria.

The disease is transmitted back to the mosquito if a mosquito bites a human infected with malaria. The blood that the mosquito swallows contains Plasmodium. In the insect's digestive system, Plasmodium grows rapidly and penetrates the insect's entire body, including the salivary glands. After a time the infected insect contains active Plasmodium spores in its saliva and is able to pass the infection on to another human.

Every year, more than 500 million people suffer from Malaria and more than a million people die from it. Although drugs such as chloroquinine are effective against some forms of the disease, many strains of malaria-causing Plasmodium sporozoans are resistant to these drugs. To date, the most effective way to control malaria is to destroy breeding areas for Anopheles mosquitoes. This interrupts the life cycle of Plasmodium and thus prevents the spread of malaria.

To read more about Malaria, check out the Malaria Factsheet maintained by the World Health Organization.

Found in Africa and the Middle East, River blindness is a human disease caused by a parasitic roundworm that enters the body when a black fly, which has picked up the roundworm by biting an infected human, bites another victim.

The roundworm larvae deposited by the black fly quickly grow into threadlike adult worms, which can live under the skin for as long as twelve years. It is not the adult worms that cause this dreadful disease but their offspring- millions of microworms that swarm through the skin and eyes.

Blindness is not the only effect of this disease. As the microworms migrate under the skin, intolerable itching results. Over time, the skin begins to decay and often loses its pigment.

The scourge of river blindness has economic implications as well. When the rate of blindness in the village becomes significant, fearful young people abandon their homes. Farm production in fertile river valleys is curtailed because there are limited laborers to grow and harvest the crops.

Sleeping Sickness

Sleeping sickness or human African trypanosomiasis is a parasitic disease of people and animals, caused by protozoa of species Trypanosoma brucei and transmitted by the tsetse fly. The disease is endemic in certain regions of Sub-Saharan Africa, covering about 36 countries and 60 million people.

It is estimated that 50,000 to 70,000 people are currently infected, the number having declined somewhat in recent years. Three major epidemics have occurred in recent history, one lasting from 1896–1906 and the other two in 1920 and 1970. In 2008 there was an epidemic in Uganda.

Clinical features
Symptoms begin with fever, headaches, and joint pains. As the parasites enter through both the blood and lymph systems, lymph nodes often swell up to tremendous sizes. Winterbottom's sign, the telltale swollen lymph nodes along the back of the neck may appear. If untreated, the disease slowly overcomes the defenses of the infected person, and symptoms spread to include anemia, endocrine, cardiac, and kidney diseases and disorders. The disease then enters a neurological phase when the parasite passes through the blood-brain barrier.

The symptoms of the second phase give the disease its name; besides confusion and reduced coordination, the sleep cycle is disturbed with bouts of fatigue punctuated with manic periods progressing to daytime slumber and nighttime insomnia. Without treatment, the disease is invariably fatal, with progressive mental deterioration leading to coma and death. Damage caused in the neurological phase can be irreversible.

In addition to the bite of the tsetse fly, the disease is contractible in the following ways:

1) Mother to child infection: the trypanosome can cross the placenta and infect the fetus, causing perinatal death.
2) Laboratories: accidental infections, for example, through the handling of blood of an infected person and organ transplantation, although this is uncommon.
3) Blood transfusion
4) Sexual contact .

These paragraphs according to Wikipedia. Read more about Sleeping Sickness there...

(This page contents credited to the book: "Biology"- by Kenneth R Miller, Ph.D. and Joseph Levine, Ph. D. (Published by Prentice-Hall, Inc. 1991, and Wikipedia)