Protist Diseases

What are protists?

The Protoctista or protists encompass a wide spectrum of eukaryotes, including protozoans ('simple Animals') and Algae, such as seaweeds. A protoctist is a type of eukaryote that isn't a fungus, plant, or animal. They are generally single-celled, or occur as clusters of similar Cells and have a nucleus. Some have animal-like cells (no cell wall) and are sometimes referred to as Protozoa, while others have plant-like cells (cellulose cell walls and chloroplasts) and are referred to as algae.

Only a few protists are pathogenic, but the diseases they cause are serious like Malaria. Often, protists need a vector to transfer from one host to the next. Vectors are very important tools for the transmission of pathogens. For example, malaria is transmitted via the Anopheles mosquito vector.

What are the different types of protists that can cause diseases?

Many organisms in this kingdom may have more in common with organisms from other kingdoms than they do with one another. An example of this is that there are compelling grounds for identifying Algae as plants rather than protists. For this reason, protists can be divided into three main categories:

• Plant-like Protists

• Animal-like Protists

• Fungus-like Protists

Plant-like protists

Plant-like protists live in soil, freshwater, saltwater or bark and produce oxygen. They include:

• Euglenoids

• Dinoflagellates

• Diatoms

• Algae (green, red & brown)

Animal-like protists

Animal-like protists are called “Protozoans” which translates to ‘first animals’. They are all unicellular and tend to be categorised by how they move:

• With Cilia (ciliates)

• With Flagella (zooflagellates)

• With Pseudopods

• Others (Parasites)

Fungus-like protists

These have cell walls and reproduce by forming spores, like fungi. Examples include:

• Water Moulds

• Slime Moulds

Protist diseases in humans

Protists can cause severe diseases in humans such as Malaria, Trypanosomiasis (African sleeping sickness), Giardiasis, and Amoebic dysentery. The most relevant and lethal today by far is malaria which remains one of the biggest causes of death in the developing world.

Example of protist disease: Malaria

Malaria is typically transmitted between infected and uninfected people via the female Anopheles mosquito. This vector insect bites humans to feed on their Blood to obtain the necessary Proteins. If the bitten person is infected with the malaria parasite, the mosquito will also become infected while collecting the blood. The parasite will then grow and multiply inside the insect. When the mosquito feeds again, it will also release the parasite into the bloodstream of the bitten individual.

Malaria transmission, therefore, requires cyclical infection of both humans and mosquitoes. Plasmodium multiplies inside both hosts and increases the chance of infecting other mosquitos and humans. Plasmodium’s life cycle has two stages: a sexual stage in the mosquito and an asexual stage inside humans.

Malaria symptoms

Malaria infection can result in various symptoms, often dividing malaria into uncomplicated or severe (complicated) disease. Following the infective mosquito bite, there is an incubation period before symptoms appear that can range from a week to a year, but, on average, it takes 10-15 days. In some aggressive cases, malaria symptom onset can occur as fast as 24 hours after the infective mosquito bite. Shorter incubation periods are more common with the more dominant Plasmodium falciparum parasite.

Malaria symptoms include:

• Fever

• Sweats and chills

• Headaches

• Vomiting and diarrhoea

Malaria treatment

Malaria is a treatable and curable disease. Early diagnosis and treatment are important to reduce malaria incidence and deaths. Malaria treatments include the antimalarial drugs quinine and chloroquine, which prevent the parasite from growing and spreading within the body by inhibiting its Protein Synthesis. These drugs can also be used as prophylactics (preventive drugs) to stop an infection from occurring if a person gets bitten by an infected mosquito.

Besides prophylactic drugs, two other important preventive measures play a significant role in helping the global effort to control malaria. These are vector control strategies and the malaria vaccine. Vector control strategies include efforts to either reduce the number of malaria vector mosquitos or avoid getting bitten by them. In summary, prevention techniques include:

• Sleeping under mosquito nets.

• Wearing insect repellent to avoid bites.

• Removing standing water sources to help reduce mosquitos

Example of protist disease: African Sleeping sickness

Like malaria, sleeping sickness disease is spread via a vector. The Tsetse fly is a species native to Africa and it spreads a protist disease called sleeping sickness, also known as Human African trypanosomiasis. This disease is caused by protists microorganisms of the species Trypanosoma brucei. (animal-like protist) The Tsetse flies are found only in sub-Saharan African countries, and it's the people who live in the rural parts of Africa that are most affected.

When the fly bites a person, the bite develops into a red sore and the person develops a fever, muscle and joint ache, swelling in the lymph glands, irritation, and headaches. It is a disease that attacks the central nervous system. Other symptoms include:

• Seizures

• Personality changes.

• Alteration of sleep patterns.

• Difficulty in walking and talking.

Example of protist disease: Giardiasis

Giardiasis is a diarrheal disease caused by a small parasite protozoan called Giardia. Giardia can be found on surfaces or in soil, food, or water that has been polluted by sick individuals or animals' faeces. If you swallow Giardia, you can develop giardiasis. Giardia is easily transmitted from person to person, as well as through polluted water, food, surfaces, and items. Swallowing contaminated drinking or recreational water is the most prevalent way for people to become ill.

The main symptoms of giardiasis are:

• smelly diarrhoea

• tummy pain or cramps

• farting (flatulence)

• dehydration

• weight loss

Example of protist disease: Amoebic dysentery

The protozoan parasite Entamoeba histolytica causes amoebic dysentery or amoebiasis. Like giardiasis, it's transmitted by contaminated drinking water or by coming into contact with anything that has touched the faeces of an infected person. It results in mild symptoms such as fever, chills, diarrhoea, and abdominal discomfort, and only 10-20% of people become ill after infection.

Plant diseases caused by plants

Downy mildew is a protist disease affecting many plants. It's spread by spores that can remain dormant in the soil for several years. It affects the yield and quality of crops as well as spoiling the appearance of ornamental plants. It's caused by several different types of protists of the Peronospora genus (water moulds or fungus-like protists) that infect leaves. By practising crop rotation, it is possible to avoid reinfection. Some of the symptoms of downy mildew include:

• Mould-like growth on the underside of the leaf.

• Discoloured blotches on the upper leaf surface.

• Severely affected leaves may shrivel and turn brown.

• Severely affected plants are often stunted and in some cases, the plant may die.