The capability of a disease agent to cause disease in a susceptible host is important to understand when studying the effects of pathogens on humans.
When a pathogen attacks its host, it typically spreads through bodily fluids such as blood and lymph. This happens by specialized cells in the organism that produce white blood cells to fight infection.
Because these cells are generally spread via the bloodstream, they are referred to as “blood” or “blood-related” diseases. These include HIV/AIDS, malaria, and tuberculosis.
While all of these diseases have symptoms that make people feel sick, they are usually not diagnosed and treated until it causes serious health problems such as HIV/AIDS or tuberculosis.
This is because people do not always recognize symptoms of infectious diseases, nor do they always seek treatment when they do start feeling sick.
Disease-causing agents and their effects
Disease-causing agents are a class of compound captured within the term ‘compounds that cause disease’. Compounds that cause disease are classified as pathogens, or diseases affecting humans.
The word ‘disease’ was chosen as it is an adjective, not a noun, so it can apply to both its natural and artificial forms. For example, hepatitis A and Hepatitis B vaccines are designed as safe and effective ways to prevent hepatitis C.
Although most disease-causing agents do not have any obvious effects on the body, there are some signs and symptoms they may have. Some signs and symptoms of infectious diseases are:
vomiting (sometimes called ‘sickening’), loss of appetite, tiredness, sleeping more than usual, headaches and/or dizziness, unusual bruising or bleeding (sometimes called ‘the sickest blood you ever saw’), changes in skin color orfatigue, unusual behavior (such as aggressive) or death.
Pathogenicity and virulence compared
There are several ways that a pathogens virulence can be measured. These include:
How much damage it causes in an animal or person it infects. How effectively it spreads in its environment. How often it re-emerges into its natural environment.
These factors play a role in determining the capability of a pathogens virulence to cause disease in an animal or person. For example, low virulence may be enough to cause mild disease in an individual, while highly virulent forms may never fail to cause very severe disease.
An example of this is the case where humans are infected with the zoonotic chikungunya virus, which causes chikungunya fever. The highly virulent form has such poor symptomatic treatment recovery that treating just one individual would not prevent another person from being infected.
Factors that affect the pathogenicity of a disease-causing agent
As discussed earlier, the ability of a disease-causing agent to cause disease in an animal is partially dependent on the severity of its pathogenicity.
However, this does not explain why certain pathogens have been shown to be capable of causing disease in humans. After all, it would not make sense for a bacteria that can cause pneumonia to be adopted as a vaccine against obesity!
Despite being considered human carcinogens, some pathogens have shown to be less potent than others in causing disease. This seems to have something to do with weather or environment effects on the pathogen and whether it was underdeveloped or developed during its evolutionary journey.
As discussed earlier, genetic factors play a role in determining if an organism is capable of causing disease in an individual. This article will go into more detail about these changes and how they affect the capability of diseases-causing agents to cause disease.
The nature of the host
The nature of a disease agent is different for each disease. HIV and the flu are virus, so any object or place can become a host. This is why healthcare workers wear protective gear when treating someone with the flu!
Disease agents such as Ebola aren’t normal body processes, but they do have a cycle. The key process that occurs in and around the cell is called an evolution cycle. This includes temperature regulation, cell division, and other minor processes.
During an evolution cycle, one or more functions may occur incorrectly or not at all. For example, during cell division, some walls may be erased, others may become nuclei instead of daughter cells.
These missing steps make it difficult to predict when an infection will occur or what type of infection it will be.
The nature of the disease-causing agent
As described in the bullet point, a disease agent can cause disease in a susceptible host. This occurs when the agent enters the body and affects an enzyme system within the body.
Enzyme systems within the body regulate processes such as immune responses, nutrient uptake, and cell division. When an enzyme system is affected, it regulates or directs other parts of the body’s system to carry out specific functions.
Disease agents are classified by whether or not they cause life-threatening conditions. If a disease agent does cause such conditions, it is classified as a life-ending condition. These types of disease agents have characteristics that make them resistant to treatment.
These characteristics include strong negative effects on the immune system, low levels of production by organs and tissues, and resistance to therapies used for other conditions.
Pathogenicity and evolution
Pathogenicity is the ability of a disease agent to cause disease in a human or animal. Disease agents can be categorized by their pathogenicity.
The four main pathogenxn included in the World Health Organization (WHO)004 classifications are: bacteria, viral, and fungal. Viruses and bacteria have similar abilities to cause disease, but bacteria can also cause disease.
In contrast, fungi do not produce an epidemic virus, but instead use a mycelium to spread its infection. This mode of infection does not cause disease in humans, but does affect other organisms such as plants and animals.
Human pathogens such as plague, cholera, and ebola are considered human Disease Agents (HDAs). Other HDAs such as botulism or vaccinia are plant pathogens that create diseases in humans.
Examples of highly pathogenic infectious diseases
There are many examples of highly pathogenic diseases, especially when you look at disease outbreaks. Many of these diseases are still active, making them significant forces for natural balance.
The Black Plague, which killed an estimated 20 to 30 percent of the world’s population in the middle to late 17th century, is an example. This disease was extremely contagious, caused symptoms quickly and lasted for several weeks.
The bubonic plague is another example of a deadly infectious disease that can infect a specific group of people. These people are typically health professionals, as they must be knowledgeable about signs and symptoms.
Examples of moderately pathogenic infectious diseases
There are several examples of moderately pathogenic diseases that humans can be exposed to. These include HIV, Ebola, and Marrow Transplants.
HIV is the human immunodeficiency virus. It damages the immune system and forces the body to rely on the outside world for survival.
Although it is rare, people can become infected with HIV. However, because it attacks the immune system, it is much more difficult to detect than a straightforward virus like hepatitis A or B.
Because of this, diagnosis can be difficult. People must be actively aware that they have been exposed and that they need to seek medical care if symptoms develop.
Similarly, Ebola is a deadly disease that attacks the nervous system. Because of this, cases are very hard to detect.
