Germs: Bacteria, Viruses, Fungi, and Protozoa

Categories: MalariaMicroorganisms
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A virus is a small infectious agent that replicates only inside the living cells of other organisms. Viruses can infect all types of life forms, from animals and plants to bacteria and archaea.


Like living organisms, viruses contain nucleic acids and proteins. Inside living cells, viruses can reproduce, but not by the process of mitosis like most living cells. Viruses lack some characteristics of living organisms. Outside of living cells, viruses are not alive.


A virus structure can be one of the following: icosahedral, enveloped, complex or helical.

These viruses appear spherical in shape, but a closer look actually reveals they are icosahedral.

Icosahedral-These viruses appear spherical in shape, but a closer look actually reveals they are icosahedral. The icosahedron is made up of equilateral triangles fused together in a spherical shape. This is the most optimal way of forming a closed shell using identical protein sub-units. The genetic material is fully enclosed inside of the capsid. Viruses with icosahedral structures are released into the environment when the cell dies, breaks down and lyses, thus releasing the virions.

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Examples of viruses with an icosahedral structure are the poliovirus, rhinovirus, and adenovirus.

Envelope- This virus structure is a conventional icosahedral or helical structure that is surrounded by a lipid bilayer membrane, meaning the virus is encased or enveloped.

Complex- These virus structures have a combination of icosahedral and helical shape and may have a complex outer wall or head-tail morphology. The head-tail morphology structure is unique to viruses that only infect bacteria and are known as bacteriophages.

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The head of the virus has an icosahedral shape with a helical shaped tail.


This virus structure has a capsid with a central cavity or hollow tube that is made by proteins arranged in a circular fashion, creating a disc like shape. The disc shapes are attached helically (like a toy slinky) creating a tube with room for the nucleic acid in the middle. All filamentous viruses are helical in shape.

Diseases Caused By Viruses:

List of diseases caused by viruses:


A fungus is any member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. SCIENTIFIC NAME (Fungi)


Most fungi grow as tubular filaments called hyphae. An interwoven mass of hyphae is called a mycelium. The walls of hyphae are often strengthened with chitin, a polymer of N-acetylglucosamine. … Fungi disperse themselves by releasing spores, usually windblown. … Fungi are heterotrophic.


Specific Diseases Caused by Fungi:

1. Candida Infection-Candidiasis is a common yeast infection that affects many people. There are hundreds of thousands of candida microorganisms that normally live in our bodies. They can be found in the mouth, gut, and female organ. Symptoms vary according to different areas infected. Most candida infections are mild but resistance to drug therapy is becoming more common, thereby making some infections tougher to treat. 2. Fungal Meningitis-This fungal infection is caused by Cryptococcus, which leads to inflammation of the thin membranes that cover the brain and spinal cord. A common life-threatening condition that affects many HIV patients, infection is usually acquired through inhalation of fungal cells in the air. These organisms usually thrive in the body of people whose immune systems are weakened.

3. Aspergillus Infection-Aspergillus molds spread in the air and cause serious infections in the lungs and blood of people with weak immune systems, such as those with cancer, HIV, or bone marrow recipients. They are found in air conditioning systems, in beddings, plants, basements, dust, and almost everywhere. These molds act as a potent allergen, which can trigger asthma. Symptoms include coughing, wheezing and fever. Infection may be treated with antifungal medications such as Voriconazole.

4. Athlete’s Foot-This common fungal infection is also known as tinea pedis, which causes redness, itching, peeling, blisters, burning, and sores on the foot. The fungus favors warm and moist environments such as socks, shoes, locker rooms, swimming pools, and public showers. Infection is common in summer or in warm and humid climates. The fungus lives on dead tissues of the toenails, skin, and hair.

5. Jock Itch-This common skin infection, also known as tinea cruris, is caused by fungi called tinea. This fungus lives in warm and moist areas like the genitals, buttocks, and the inner thighs. Infections frequently occur in summer as well as in warm and wet climates. It causes red, itchy rashes that are ring-shaped. Direct contact with infected individuals can cause the spread of infection. Symptoms include itching, burning, redness, peeling, flaking or cracked skin. Treatment includes the use of over-the counter creams for mild infection and prescription-strength antifungals for severe infection. Keep affected areas clean and dry. It is also important to change your underwear daily.

6. Ringworm-Although the name sounds like the infection is caused by a worm, tinea corporis or ringworm is caused by a fungus. Flat, red sores, some with the outer parts raised, appear anywhere on the skin. Patches of raised skin sores may overlap and skin may appear scaly. The fungal infection may spread through direct contact with skin of an infected person and indirectly through contaminated objects such as clothes or furniture. Warm, humid climates favor the growth of these fungi.


Bacteria constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals.


There are 3 types of bacteria based on their shapes such as: Bacteria grow in number not in size, but they make copies of themselves by dividing into half. There are three basic shapes of bacteria: Rod shaped bacteria called as bacilli.

Spherical shaped bacteria called as cocci.
Curved shaped bacteria called as spirilla.

Some of the bacteria exist as single cells, others exist as cluster together.

Respiration in bacteria:

Anaerobic bacteria: does not require oxygen for respiration. Aerobic bacteria: require oxygen for respiration.

Gram staining bacteria are a method of differentiating bacterial species into two large groups, which are based on their chemical and physical properties of their cell wall. Gram positive bacteria: Those bacteria when they are stained in gram stain results in purple colour. Gram negative bacteria: Those bacteria when they are stained in gram stain results in pink colour.

Locomotion of bacteria:

They move around by using their locomotion organs such as cilia and flagella.

Nutrition of bacteria:
They exhibits different modes of nutrition level such as-

Autotrophic bacteria: These bacteria are able to synthesize their own food. For e.g.: Phototropic bacteria and chemosynthetic bacteria Heterotrophic bacteria: These bacteria are unable to synthesize their own food, hence they depends on other organic materials. For e.g.: saprophytic bacteria-these bacteria feeds on dead and decaying matter. Symbiotic bacteria: These bacteria have a mutual benefit from other organisms. For e.g.: nitrogen fixing bacteria (or) rhizobium. Parasitic bacteria: These bacteria are present in plants, animals and human beings. These bacteria feeds on host cells and causes harm to the host.

Reproduction in Bacteria:
The reproduction in bacteria is mainly by cell division and binary fission. In some cases few bacteria also reproduce by budding. Shape:


Harmful bacteria that cause bacterial infections and disease are called pathogenic bacteria. Bacterial diseases occur when pathogenic bacteria get into the body and begin to reproduce and crowd out healthy bacteria, or to grow in tissues that are normally sterile. Harmful bacteria may also emit toxins that damage the body. Common pathogenic bacteria and the types of bacterial diseases they cause include: Escherichia coli and Salmonella cause food poisoning.

Helicobacter pylori cause gastritis and ulcers.
Neisseria gonorrhoeae causes the sexually transmitted disease gonorrhea. Neisseria meningitidis causes meningitis. Staphylococcus aureus causes a variety of infections in the body, including boils, cellulitis, abscesses, wound infections, toxic shock syndrome, pneumonia, and food poisoning. Streptococcal bacteria cause a variety of infections in the body, including pneumonia, meningitis, ear infections, and strep throat.


Protozoa are eukaryotic microorganisms. Although they are often studied in zoology courses, they are considered part of the microbial world because they are unicellular and microscopic.


Protozoa are notable for their ability to move independently, a characteristic found in the majority of species. They usually lack the capability for photosynthesis, although the genus Euglena is renowned for motility as well as photosynthesis (and is therefore considered both an alga and a protozoan). Although most protozoa reproduce by asexual methods, sexual reproduction has been observed in several species. Most protozoal species are aerobic, but some anaerobic species have been found in the human intestine and animal rumen. Protozoa are located in most moist habitats. Free-living species inhabit freshwater and marine environments, and terrestrial species inhabit decaying organic matter. Some species are parasites of plants and animals. Protozoa play an important role as zooplankton, the free-floating aquatic organisms of the oceans. Here, they are found at the bases of many food chains, and they participate in many food webs. Size and shape.

Protozoa vary substantially in size and shape. Smaller species may be the size of fungal cells; larger species may be visible to the unaided eye. Protozoal cells have no cell walls and therefore can assume an infinite variety of shapes. Some genera have cells surrounded by hard shells, while the cells of other genera are enclosed only in a cell membrane. Many protozoa alternate between a free-living vegetative form known as atrophozoite and a resting form called a cyst. The protozoal cyst is somewhat analogous to the bacterial spore, since it resists harsh conditions in the environment. Many protozoal parasites are taken into the body in the cyst form. Most protozoa have a single nucleus, but some have both a macronucleus and one or more micronuclei. Contractile vacuoles may be present in protozoa to remove excess water, and food vacuoles are often observed.

Nutrition and locomotion. Protozoa are heterotrophic microorganisms, and most species obtain large food particles by phagocytosis. The food particle is ingested into a food vacuole. Lysosomal enzymes then digest the nutrients in the particle, and the products of digestion are distributed throughout the cell. Some species have specialized structures called cytostomes, through which particles pass in phagocytosis. Many protozoal species move independently by one of three types of locomotor organelles: flagella, cilia, and pseudopodia. Flagella and cilia are structurally similar, having a “9-plus-2” system of microtubules, the same type of structure found in the tail of animal sperm cells and certain cells of unicellular algae. How a protozoan moves is an important consideration in assigning it to a group.


Protozoan Diseases

1. Amoebiasis

This disease is caused by the sarcodina group of protozoa. They secrete enzymes that are then absorbed by the tissue of the host. Amoebiasis is transmitted through contact with infected feces. Food and water contaminated by feces is the most common route of transmission, however, oral contact with fecal matter can also cause infection. Sometimes there are no visible symptoms but some common ones include loose stools with varying amounts of blood and an inflamed colon.

2. Giardiasis

This disease is also transmitted through oral contact of feces as the parasite is found in fecal matter. If hands are not properly washed after using the bathroom or changing a diaper, it is easy to come into contact with this parasite. Drinking water which has been contaminated by this parasite or even ingesting contaminated swimming water can cause giardiasis. Symptoms include mucusy stools, diarrhea, nausea, abdominal pain and upset stomach.

3. African Sleeping Sickness

African sleeping sickness is a disease caused by the protozoa, which are carried by the tsetse fly and are transmitted to humans through tsetse fly bites. This disease is fairly damaging to the human body and can cause serious illness. Symptoms of this disease include confusion, seizures, insomnia, personality changes, weight loss, slurred speech and trouble talking or walking.

4. Leishmaniasis

This disease is caused by the Leishmania parasite. These parasites are found mainly in southern Europe, the tropics and subtropics. The most common form of this disease being spread is through the bite of a sand fly, which carries the parasite. External leishmaniasis will affect the skin and internal leshmaniasis affects the inner organs such as the spleen and liver. Those parasites that affect the skin cause sores, which will enlarge and become deeper as the disease progresses without treatment. Internal infection will cause weight loss, organ enlargement, fever and extremely high or low blood levels.

5. Toxoplasmosis

Toxoplasmosis is caused by one of the most common parasites in the world, according to the Mayo Clinic. Many of the people infected by this disease do not have any symptoms. However, for those who have weak immune systems such as infants and people suffering from chronic illnesses, this parasite can cause serious illness. Infants who are born to mothers who carry the infection can experience complications at birth. Other symptoms include body aches, fatigue, fever, sore throat and swollen lymph nodes. Symptoms are very similar to flu like symptoms and this disease can sometimes be mistaken for the flu.

6. Malaria

Malaria is a very common disease in some countries and is spread through mosquito bites of mosquitoes that have been infected by one of the many different malaria-causing parasites. In the United States, there are more than 1300 cases of malaria reported. This is mainly reported by individuals travelling to or coming from the South Asian subcontinent or the sub-Saharan Africa who may be carrying the parasite. Malaria symptoms include headache, chills, tremors, aches and shaking.

7. Babesiosis

This disease is caused by the Babesia parasite that is transmitted through ticks. It can also be transmitted through blood transfusions of donors who carry the Babesia parasite. This parasite is common throughout the United States, in cities such as New England, New Jersey, New York, Wisconsin and Minnesota. Those individuals infected with the Babesia parasite may not experience any symptoms. However, common signs and symptoms include nausea, body aches, fatigue, fever, chills, weight loss and a decreased appetite. For those who are already suffering from health problems and those who have a compromised immune system, this disease can be life threatening and cause serious health problems.

8. Trichomoniasis

This disease is caused by the protozoan parasite, Trichomonas vaginalis. This disease is most commonly transmitted sexually. It is a dangerous parasite as it can also help along HIV transmission. Symptoms of this disease differ per gender. In woman, vaginitis may occur which will cause white discharge. Men may experience a burning while urinating. This disease is treatable with an antibiotic such as metronidazole.


A parasite is an organism that lives on or in a host and gets its food from or at the expense of its host. Parasites can cause disease in humans. Some parasitic diseases are easily treated and some are not. The burden of these diseases often rests on communities in the tropics and subtropics, but parasitic infections also affect people in developed countries. Parasitic insect are those which live in close association with other living organism called the ‘host’, from whom it derives the material essential for the existence without conferring any benefit to it (host).

Ideal Characteristics of Parasites:

1. The parasite should have high searching capacity of host and utilize the host. 2. It should be fairly host specific in feeding rather than polyphagous i.e. restriction in feeding habit to a relatively few species. This implies high degree of adaptation. 3. It should be primarily to its high potential reproductive capacity, ultimately high fecundity i.e. potential for rate of increase. 4. Ability to occupy all the host inhabited niches and to survive well. 5. Adaptation to broad range of climatic conditions.

6. The parasite species should be amenable to culture in the insectory. 7. It must be efficient to bring about the death of the host. 8. It should not become a plant feeder under any conditions. 9. It should not be hyperparasites or harmful to the beneficial species. 10. Good parasite must complete with other species of natural enemies successfully for occupying food, space and shelter and must destroy the pest population within short time even at high host density. 11. There should be synchronization of life cycles of the parasite and the host.




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.

River Blindness (Onchocerciasis)

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.

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.

Cite this page

Germs: Bacteria, Viruses, Fungi, and Protozoa. (2016, Aug 26). Retrieved from

Germs: Bacteria, Viruses, Fungi, and Protozoa
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