Pathogen is abbreviated as pathogen. In biology, in the oldest and broadest sense, it is anything that can cause disease. Pathogens can also be referred to as infectious agents, infectious agents or pathogens, which generally refer to organisms and non-living organisms that can cause disease. Generally, the term pathogen is used to describe “infectious” microorganisms or vectors, such as viruses, bacteria (pathogens), fungi, protozoa, nematodes, parasites, viroids, and prions. Non-biological pathogenic factors are not called pathogens (for example: heavy metals, various chemical toxins, haze, pollution, etc.). Pathogens can invade the host through several pathways, the main pathways have different time frames for the occurrence of events, but the soil has the longest or longest potential pathogen potential. The transmission of pathogens occurs through many different routes, including airborne transmission, direct or indirect contact, sexual contact, through blood and breast milk or other body fluids, and through the fecal-oral route.
Tiny animals, such as certain types of worms and insect larvae, can also produce diseases. However, we usually call these animals parasites rather than pathogens. In the scientific research of microscopic organisms, diseases including microscopic pathogenic organisms are called microbiology, and the research of diseases that may include these pathogens is called pathology. Parasitology is also the scientific research on parasites and their host organisms. The types of pathogens include the following:
1. Prions
Prions are misfolded proteins and can transfer their misfolded state to other normally folded proteins of the same type. They do not contain any DNA or RNA, and cannot replicate except to convert existing normal proteins into a misfolded state. These abnormally folded proteins have typical features in certain diseases, such as scrapie, bovine spongiform disease (mad cow disease) and Creutzfeldt-Jakob disease.
2. Viral
Viruses are tiny particles, usually between 20 and 300 nanometers in length [8], and contain viral RNA or DNA. Viruses need the cells of the host to replicate. Some diseases caused by viral pathogens include smallpox, influenza, mumps, measles, varicella, Ebola hemorrhagic fever, human immunodeficiency virus and rubella, severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East Respiratory Syndrome Coronavirus (MERS-CoV), 2019 Novel Coronavirus (2019-nCoV), etc. The pathogenic viruses mainly come from the following families: Coronavirus, Adenovirus, Picornaviridae, Herpesviridae, Hepatoviridae, Flaviviridae, Retrovirus, Orthomyxoviridae, Paramyxoviridae, Papilloma Vacuolaviridae, Polyomaviridae, Cannonballviridae, and Togaviridae. The AIDS virus (HIV) is an important member of the retroviral family, and the disease affected 37.9 million people worldwide in 2018.
3. Bacterial
Most bacteria are between 0.15 and 700 μM in length [10], which is beneficial or harmless to humans. However, a relatively small number of pathogenic bacteria can cause infectious diseases. Pathogenic bacteria can cause disease in many ways. They can directly affect the host’s cells, produce endotoxins to destroy the host’s cells, or cause a strong enough immune response to cause the host’s cells to be destroyed. Tuberculosis, one of the bacterial diseases, is the most burdensome. It is caused by Mycobacterium tuberculosis and caused 1.5 million deaths in 2013, mainly in sub-Saharan Africa. Pathogenic bacteria cause other major global diseases, such as pneumonia caused by bacteria of the genus Streptococcus and Pseudomonas, and bacteria that cause food poisoning such as Shigella, Campylobacter and Salmonella. Pathogenic bacteria also cause infections such as tetanus, typhoid fever, diphtheria, syphilis and leprosy.
4. Fungi
Fungi are eukaryotes that can act as pathogens. There are about 300 species of fungi known to be pathogenic to humans [12], including Candida albicans, the most common cause of thrush, and Cryptococcus neoformans, which may cause severe meningitis. The typical fungal spore size is <4.7μm, but some spores may be larger.
5. Algae
Algae are single-celled plants, and although pathogenic variants do exist, they are usually not pathogenic. Protothecosis (Protothecosis) is a disease found in dogs, cats, cattle and humans. It is caused by a type of chlorophyll-deficient green alga (called stratum corneum).
6. Other parasites
Some eukaryotes, including many protozoa and worms, are human parasites.
Their treatment methods are as below:
1. Prions
Despite many attempts, no therapy can be shown to prevent the progression of prions.
2. Viruses
For certain viral pathogens, there are multiple prevention and treatment options. Vaccines are a common and effective preventive measure against many viral pathogens. Vaccines can stimulate the host’s immune system to respond, so when a potential host encounters a virus in the wild, its immune system can quickly defend against infection. There are vaccines against viruses including measles, mumps, rubella virus and influenza virus. There are currently no vaccines available for certain viruses such as HIV, dengue virus and chikungunya.
The treatment of viral infections usually involves treating the symptoms of the infection, rather than providing any drugs that affect the viral pathogen itself. Treating the symptoms of a viral infection is to allow the host’s immune system time to develop antibodies against the viral pathogen, thereby clearing the infection. In some cases, the virus must be treated. One example is HIV, which requires the use of antiretroviral drugs, also known as ART or HAART, to prevent the loss of immune cells and the further development of AIDS.
3. Bacteria
Similar to viral pathogens, infections with certain bacterial pathogens can be prevented by vaccines [28]. Vaccines against bacterial pathogens include anthrax vaccine and Streptococcus pneumoniae vaccine. Many other bacterial pathogens lack vaccines as a preventive measure, but these bacterial infections can usually be treated or prevented with antibiotics. Many other bacterial pathogens lack vaccines as a preventive measure, but these bacterial infections can usually be treated or prevented with antibiotics. Common antibiotics include amoxicillin, ciprofloxacin/dexamethasone, and dexamethasone. Each antibiotic has an effective antibacterial effect, and has a different mechanism to kill bacteria. For example, doxycycline inhibits the synthesis of new proteins in gram-negative and gram-positive bacteria, leading to the death of the affected bacteria.
Due to excessive prescriptions without antibiotics, some bacterial pathogens have developed resistance to antibiotics and are becoming difficult to treat with traditional antibiotics. A type of Staphylococcus aureus called MRSA is an example of a bacterial pathogen that is difficult to treat with common antibiotics. The Centers for Disease Control (CDC) estimated in a report released in 2013 that at least 2 million people in the United States are infected with drug-resistant bacteria each year, and at least 23,000 people die from these infections.
4. Fungi
Infections by fungal pathogens can be treated with antifungal drugs. Fungal infections such as tinea pedis, tinea corporis and dermatophytosis are all skin infections, which can be treated with topical antifungal drugs, Kezima Nilai. Other common fungal infections include the yeast strain Candida albicans. Candida can cause oral or throat infections, commonly called thrush, or candida vulvovaginitis. These internal infections can be treated with antifungal creams or oral medications. Commonly used antifungal drugs for internal infections, including echinocandin series drugs and fluconazole.
5. Algae
Algae are not generally considered pathogens, but the protozoan genus is known to cause disease in humans. The treatment method for this infection is currently being studied, and there is no consistent treatment method in clinical treatment.
Pathogens are transmitted during sexual contact with animals
Many pathogens can be spread through sexual contact. In pathogenic bacteria, through the process of natural genetic transformation, the transformation between cells of the same species can occur through sexual contact. Transformation involves the transfer of DNA from the donor cell to the recipient cell, and then through genetic recombination, the DNA of the donor cell is integrated into the recipient’s genome. Examples of bacterial pathogens that can be transformed naturally are: Helicobacter pylori, Haemophilus influenzae, Legionella, Neisseria gonorrhoeae, and Streptococcus pneumoniae.
Eukaryotic pathogens can often interact sexually through processes involving meiosis and gametogenesis. Meiosis involves the reorganization between them, and the reorganization between them. Examples of sexually capable eukaryotic pathogens include: protozoan parasite protozoa infection, Plasmodium falciparum, Toxoplasma, Trypanosoma brucei, Giardia lansii, and the fungi Aspergillus fumigatus, Candida albicans and Cryptococcus neoformans.
When two or more viral genomes enter the same host cell, the viruses may also interact sexually. This process involves the pairing and recombination of homologous genomes, and this process between them is called “multiplicity reactivation.” Viruses undergoing this process include herpes simplex virus, human immunodeficiency virus and vaccinia virus.
The sexual process in bacteria, microbial eukaryotes and viruses all involve the recombination of homologous genomes, causing damage to the pathogen’s genome through the defense of their respective target hosts, which seems to promote the repair of genome damage.
