Unit 6: Pathogens

What are pathogens? Pathogens can be any organisms that cause diseases. There are a few types of pathogens, including bacteria (pathogenic bacteria), virus, fungus, protein or chemical.

Bacteria

Not all bacteria causes disease, in fact, most are essential to our lives, such as E. Coli. Those that are harmful to us are called as pathogenic bacterias.

Tuberculosis

Tuberculosis (TB) is a disease caused by bacteria called Mycobacterium tuberculosis. With symptoms including persistent cough, weight loss, fever and loss of appetite, TB is a serious condition. With 10 million cases recorded in 2016 worldwide, the number of deaths in the same year is more than 1.2 million. It can be transmitted through air. When a person breathe in TB, it will settle in his/her lung and may get to other organs through the bloodstream.

(Scanning electron micrograph of Mycobacterium tuberculosis)

Anthrax

Anthrax is a disease caused by Bacillus anthracis, a bacteria which can survive in soil for decades due to the protection of endospore, which is formed by the bacteria to protect itself in harsh environment by storing the important parts of the bacteria in it. After it was intaken by animals or human through inhalation, ingestion or wound on skin, it will start dividing rapidly and releases Anthrax toxin, evading the immune system and may kill the host animal. It is a very deadly thus it have been used as a biological warfare weapon.

Bacillus anthracis

Cutaneous anthrax lesion on the neck

Virus

Structure of virus

Virus is a parasite which consists of DNA (DNA viruses) / RNA (RNA viruses) and a capsid, which is a protein coat capsulating the genetic information. Some viruses have a layer of extra protection called an envelope, which is made up of lipid. Those with an envelope are called enveloped viruses, while others are called naked viruses. Surface proteins can also be found on the surface of the capsid of the envelope. Viruses have the ability to infect other organisms’ cells by replicating itself in other cells.

How virus works

Viruses needs to be replicated to survive, however, it can replicate itself on its own, therefore, a virus needs to enter another cell to replicate itself. To enter other cells, there are spikes on its surface, allowing it to attach to cells with corresponding receptors. Virus will infect the cell and take over it’s cellular mechanism to produce new viruses. The new viruses will then be released to infect even more cells.

AIDS

The Acquired ImmunoDeficiency Syndrome (AIDS) is caused by Human Immunodeficiency Virus (HIV). HIV infects the human immune system by targeting the white blood cells, weakening the immune system, causing more diseases, or even cancer to develop in the body.

(Different types of fungus, BorgQueen / Wikimedia Commons / CC-BY-SA-2.5)

Fungus

Fungi are simple organisms that relies on digesting organic matters to survive. They do not have the ability to move, but they can form pores and from one place to another. Fungi were first classified as a member under the kingdom Plantae, but in 1969, Robert Whittaker proposed that fungi are saprotrophic, while plants are autotrophic (they produces food on their own) and animals are heterotrophic (they can’t produce own food, they rely on other sources of nutrition), since then, fungi became a separate kingdom.

Athlete’s foot

Athlete’s foot is a skin infection caused by several different fungi which live on the warm and moist skin between toes, patients with athlete’s foot will feel itchy, the infection skin may become red. It may also spread to toenails and the hands.

A severe case of athlete’s foot

Microscopic view of an atlehete's foot fungus

(Ecorahul / Wikimedia Commons / CC-BY-SA-3.0)

Candidiasis

Candidiasis is caused by infection of candida (or called as thrush or yeast infection based on the location of infection), a category of 50+ species under fungus. It commonly infects the mouth, vagina or penis. Signs and symptoms include white patches on the tongue, problem swallowing, genital itching or burning.

(White patches on the tongue due to infection of candida, James Heilman, MD / Wikimedia Commons / CC-BY-SA-3.0)

Prion

Proteins can be infectious. The word “prion” came from the phrase “proteinaceous infectious particle”. Prions are misfolded proteins that can induce other proteins to misfolded, thus making them malfunction. Besides, they are resistant to proteases, heat and radiation.

BSE infected cow losing ability to stand

Bovine spongiform encephalopathy

BSE, a.k.a. mad cow disease, is a neurodegeneration disease, which causes incurable loss of structure or function of neurons, that can be found in cattles. It was caused by prion. Infected cattles will slowly lose their ability to control muscles and have unstable emotions. Intaking prion infected meat (for example, eating dead bodies of infected cows) will cause infection.

Creutzfeldt–Jakob disease

CJD is another prion caused disease, it is quite rare, only about 350 cases in USA per year. CJD can infect human, resulting in memory loss, visual disturbances etc. 70% patients will die within a year.

Normal brain cells

CJD patient’s brain cell

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