Difference Between Disease and Infection

Disease and infection are two terms that are often used interchangeably, but they have distinct differences. Understanding these differences is important for proper diagnosis, treatment, and prevention of various illnesses.

What is a Disease?

Disease is a condition of the body, caused by the effects of excessive or unusual stimuli. It occurs with impaired homeostasis and reduced quality and efficiency of the life processes. It is a deviation from the normal life of the organism, accompanied by structural and functional changes.

The diseases can be contagious or non- contagious. They can be caused by:

• Injury;

• Infection;

• Hereditary factors;

• Environmental factors;

• Lifestyle – e.g. sedentary lifestyle, unhealthy diet, etc.

The disease passes through the following stages:

• Latent (hidden) stage: The latent stage covers the period from the onset of the pathogenic factor to the first clinical sign. In infectious diseases, the latent stage is called incubation period. During this period the organisms are clinically healthy and show no visible signs of disease. At molecular, cellular and organ level, pathogenic changes induced by the action of the pathogenic factor develop. Protective-adaptive reactions also develop. In some cases, these may result in the destruction of the pathogenic agent. The latency period has a different duration and is determined by the strength and specific features of the pathogenic factor, and by the state of reactivity of the organism.

• Prodromal stage: The prodromal stage covers the period from the appearance of the first clinical sign to the formation of the complete complex of symptoms of the disease. Through it, the defensive mechanisms of the organism are weakened. Metabolic, structural and functional disorders are exacerbated and manifest through external symptoms.

• Stage of full clinical expression: During this stage, the pathological processes completely dominate over the protective-adaptive ones. Symptoms specific to the disease occur.

• Ending stage: The last stage of the disease can continue to healing or pass into pathological condition and death.

The symptoms of a disease can be:

• Subjective – show how the body feels;

• Objective – observable symptoms;

• Conditionally-subjective – common symptoms occurring in a wide range of diseases.

What is an Infection?

Infection is a contagion of the body tissues with pathogenic microorganisms, their multiplication in cells and the specific immune response of the body to these microorganisms and the toxins they produce. Infections are caused by viruses and bacteria. Larger organisms such as macroparasites (worms, ticks) and fungi (causing various mycoses) can also be a source of infection.

The ability of the microorganisms to cause an infection, whether it is clinically expressed or lacking symptoms, is called infectiousness.

The different species of macroorganisms in which a certain microorganism can cause infection is referred to as its infectious spectrum. The infectious spectrum of some microorganisms is very broad. For example, rabies virus causes infections in all mammal species. Other microbes have a narrow infectious spectrum. For example, in natural conditions the causes of gonorrhea and syphilis cause infections and diseases only in humans.

The symptoms of the infection depend on the type of the disease, and often on the type of the microorganism that causes them. Some of them affect the whole body:

• fatigue;

• loss of appetite;

• weight loss;

• temperature and chills;

• night sweats;

• pain.

There are also symptoms affecting individual parts of the body:

• skin – rashes;

• respiratory organs – cough, stuffy nose, runny nose;

• digestive tract – vomiting, abdominal pain.

Differences: Disease and Infection

While infections can cause diseases, not all infections lead to the development of a disease. In some cases, the immune system can clear the infection before it causes any significant harm. For example, many people are exposed to the influenza virus every year, but only a subset of them develop the flu, which is a disease caused by the virus.

Moreover, some diseases are not caused by infections. For instance, cancer is a group of diseases characterized by the uncontrolled growth and spread of abnormal cells. Cancer can develop due to various factors such as genetic mutations, exposure to carcinogens, or immune system dysfunction. In contrast, infections can lead to cancer in some cases, such as the human papillomavirus (HPV) which can cause cervical cancer.

Another important difference between infections and diseases is the mode of transmission. Infections can be transmitted from one person to another through various routes such as air, water, food, or bodily fluids. Infections can also be transmitted through vectors such as mosquitoes, ticks, or other animals that carry and spread the pathogenic microorganisms. In contrast, diseases are not directly transmissible, but they may have underlying causes such as infections that can be transmitted.

The following table highlights the major differences between a Disease and an Infection:

Characteristics	Disease	Infection
Definition	Disease is a condition of the body, caused by the effects of excessive or unusual stimuli. It is a deviation from the normal life of the organism, accompanied by structural and functional changes.	Infection is a contagion of the body tissues with pathogenic microorganisms, their multiplication in the cells and the specific immune response of the body to these microorganisms and the toxins they produce.
Causes	Diseases can be caused by injury, infection, hereditary factors, lifestyle, environmental factors, etc.	Infections are caused by viruses, bacteria, macroparasites, and fungi.
Symptoms	Nausea, vomiting, swelling, pain, breathing problems, diarrhea, bleeding symptoms, etc.	Painful swollen wound, appearance of pus; fever, runny nose, cough, muscle and joint pain, fast heartbeat, dizziness, etc.
Transmissibility	The diseases can be contagious or non- contagious.	The infections are contagious. They can transfer from an infected person to a healthy one.

Conclusion

The diagnosis and treatment of infections and diseases require different approaches. Infections are typically diagnosed by detecting the presence of the pathogenic microorganisms in the affected tissues or fluids.