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A list of the more common and well-known diseases associated with infectious pathogens is provided and is not intended to be a complete listing.
Infectious pathogen-associated diseases include many of the most common and costly chronic illnesses. The treatment of chronic diseases accounts for 75% of all US healthcare costs (amounting to $1.7 trillion in 2009).
The U.S. Centers for Disease Control and Prevention (CDC) publishes a journal "Emerging Infectious Diseases" that identifies the following factors contributing to disease emergence:
- Microbial adaption; e.g. genetic drift and genetic shift in Influenza A
- Changing human susceptibility; e.g. mass immunocompromisation with HIV/AIDS
- Climate and weather; e.g. diseases with zoonotic vectors such as West Nile Disease (transmitted by mosquitoes) are moving further from the tropics as the climate warms
- Change in human demographics and trade; e.g. rapid travel enabled SARS to rapidly propagate around the globe
- Economic development; e.g. use of antibiotics to increase meat yield of farmed cows leads to antibiotic resistance
- Breakdown of public health; e.g. the current situation in Zimbabwe
- Poverty and social inequality; e.g. tuberculosis is primarily a problem in low-income areas
- War and famine
- Bioterrorism; e.g. 2001 Anthrax attacks
- Dam and irrigation system construction; e.g. malaria and other mosquito borne diseases
For infecting organisms to survive and repeat the infection cycle in other hosts, they (or their progeny) must leave an existing reservoir and cause infection elsewhere. Infection transmission can take place via many potential routes:
- Droplet contact, also known as the "respiratory route", and the resultant infection can be termed airborne disease. If an infected person coughs or sneezes on another person the microorganisms, suspended in warm, moist droplets, may enter the body through the nose, mouth or eye surfaces.
- Fecal-oral transmission, wherein foodstuffs or water become contaminated (by people not washing their hands before preparing food, or untreated sewage being released into a drinking water supply) and the people who eat and drink them become infected. Common fecal-oral transmitted pathogens include "Vibrio cholerae", "Giardia" species, rotaviruses, "Entameba histolytica", "Escherichia coli", and tape worms. Most of these pathogens cause gastroenteritis.
- Sexual transmission, with the resulting disease being called sexually transmitted disease
- Oral transmission, Diseases that are transmitted primarily by oral means may be caught through direct oral contact such as kissing, or by indirect contact such as by sharing a drinking glass or a cigarette.
- Transmission by direct contact, Some diseases that are transmissible by direct contact include athlete's foot, impetigo and warts
- Vehicle Transmission, transmission by an inanimate reservoir (food, water, soil).
- Vertical transmission, directly from the mother to an embryo, fetus or baby during pregnancy or childbirth. It can occur when the mother gets an infection as an intercurrent disease in pregnancy.
- Iatrogenic transmission, due to medical procedures such as injection or transplantation of infected material.
- Vector-borne transmission, transmitted by a vector, which is an organism that does not cause disease itself but that transmits infection by conveying pathogens from one host to another.
The relationship between "virulence versus transmissibility" is complex; if a disease is rapidly fatal, the host may die before the microbe can be passed along to another host.
A number of studies have reported associations between pathogen load in an area and human behavior. Higher pathogen load is associated with decreased size of ethnic and religious groups in an area. This may be due high pathogen load favoring avoidance of other groups, which may reduce pathogen transmission, or a high pathogen load preventing the creation of large settlements and armies that enforce a common culture. Higher pathogen load is also associated with more restricted sexual behavior, which may reduce pathogen transmission. It also associated with higher preferences for health and attractiveness in mates. Higher fertility rates and shorter or less parental care per child is another association that may be a compensation for the higher mortality rate. There is also an association with polygyny which may be due to higher pathogen load, making selecting males with a high genetic resistance increasingly important. Higher pathogen load is also associated with more collectivism and less individualism, which may limit contacts with outside groups and infections. There are alternative explanations for at least some of the associations although some of these explanations may in turn ultimately be due to pathogen load. Thus, polygny may also be due to a lower male:female ratio in these areas but this may ultimately be due to male infants having increased mortality from infectious diseases. Another example is that poor socioeconomic factors may ultimately in part be due to high pathogen load preventing economic development.
An emerging infectious disease (EID) is an infectious disease whose incidence has increased in the past 20 years and could increase in the near future. Emerging infections account for at least 12% of all human pathogens. EIDs are caused by newly identified species or strains (e.g. Severe acute respiratory syndrome, HIV/AIDS) that may have evolved from a known infection (e.g. influenza) or spread to a new population (e.g. West Nile fever) or to an area undergoing ecologic transformation (e.g. Lyme disease), or be "reemerging" infections, like drug resistant tuberculosis. Nosocomial (hospital-acquired) infections, such as methicillin-resistant Staphylococcus aureus are emerging in hospitals, and extremely problematic in that they are resistant to many antibiotics. Of growing concern are adverse synergistic interactions between emerging diseases and other infectious and non-infectious conditions leading to the development of novel syndemics. Many emerging diseases are zoonotic - an animal reservoir incubates the organism, with only occasional transmission into human populations.
A contagious disease is a subset category of transmissible diseases, which are transmitted to other persons, either by physical contact with the person suffering the disease, or by casual contact with their secretions or objects touched by them or airborne route among other routes.
Non-contagious infections, by contrast, usually require a special mode of transmission between persons or hosts. These include need for intermediate vector species (mosquitoes that carry malaria) or by non-casual transfer of bodily fluid (such as transfusions, needle sharing or sexual contact).
The boundary between contagious and non-contagious infectious diseases is not perfectly drawn, as illustrated classically by tuberculosis, which is clearly transmissible from person to person, but was not classically considered a contagious disease. In the present day, most sexually transmitted diseases are considered contagious, but only some of them are subject to medical isolation.
Outbreaks of zoonoses have been traced to human interaction with and exposure to animals at fairs, petting zoos, and other settings. In 2005, the Centers for Disease Control and Prevention (CDC) issued an updated list of recommendations for preventing zoonosis transmission in public settings. The recommendations, developed in conjunction with the National Association of State Public Health Veterinarians, include educational responsibilities of venue operators, limiting public and animal contact, and animal care and management.
Humans contract the disease after a bite by an infected tick of the species "Amblyomma americanum".
Those with an underlying immunodeficiency (such as HIV) appear to be at greater risk of contracting the disease. Compared to HME, ewingii ehrlichiosis has a decreased incidence of complications.
Like "Anaplasma phagocytophilum", the causative agent of human granulocytic ehrlichiosis, Ehrlichia ewingii infects neutrophils. Infection with "E. ewingii" may delay neutrophil apoptosis.
Contact with farm animals can lead to disease in farmers or others that come into contact with infected animals. Glanders primarily affects those who work closely with horses and donkeys. Close contact with cattle can lead to cutaneous anthrax infection, whereas inhalation anthrax infection is more common for workers in slaughterhouses, tanneries and wool mills. Close contact with sheep who have recently given birth can lead to clamydiosis, or enzootic abortion, in pregnant women, as well as an increased risk of Q fever, toxoplasmosis, and listeriosis in pregnant or the otherwise immunocompromised. Echinococcosis is caused by a tapeworm which can be spread from infected sheep by food or water contaminated with feces or wool. Bird flu is common in chickens. While rare in humans, the main public health worry is that a strain of bird flu will recombine with a human flu virus and cause a pandemic like the 1918 Spanish flu. In 2017, free range chickens in the UK were temporarily ordered to remain inside due to the threat of bird flu. Cattle are an important reservoir of cryptosporidiosis and mainly affects the immunocompromised.
Porcine circoviral disease (PCVD) and Porcine circovirus associated disease (PCVAD), is a disease seen in domestic pigs. This disease causes illness in piglets, with clinical signs including progressive loss of body condition, visibly enlarged lymph nodes, difficulty in breathing, and sometimes diarrhea, pale skin, and jaundice. PCVD is very damaging to the pig-producing industry and has been reported worldwide. PCVD is caused by porcine circovirus type 2 (PCV-2).
The North American industry endorses "PCVAD" and European use "PCVD" to describe this disease.
Ehrlichiosis ewingii infection is an infectious disease caused by an intracellular bacteria, "Ehrlichia ewingii". The infection is transmitted to humans by the tick, "Amblyomma americanum". This tick can also transmit "Ehrlichia chaffeensis", the bacteria that causes human monocytic ehrlichiosis (HME).
Postweaning multisystemic wasting syndrome ("PMWS") is the classic PCVD entity, caused by PCV-2. PCV-2 has a near universal distribution – present in most pig herds. In contrast, PMWS is more sporadic in its distribution. Experimental induction of PMWS has not been achieved by PCV-2 infection alone, using infectious DNA clones of the virus or a pure form of PCV-2 derived from infectious DNA clones. Therefore, it is assumed that PMWS is a multifactorial disease. PCV-2 is necessary but not sufficient for the development of PMWS. However, viral infection by itself tends to cause only mild disease, and co-factors such as other infections or immunostimulation seem necessary for development of severe disease.[1] For example, concurrent infection with porcine parvovirus or PRRS virus, or immunostimulation lead to increased replication of PCV-2 and more severe disease in PCV-2-infected pigs. There is no significant correlation of the disease with virus sequence variation with affected and control pigs.
A vaccine is available, called "Chinese Live Attenuated EIA vaccine", developed in China and widely used there since 1983. Another attenuated live virus vaccine is in development in the United States.
Reuse of syringes and needles is a risk factor for transfer of the disease. Currently in the United States, all horses that test positive must be reported to federal authorities by the testing laboratory. EIA-positive horses are infected for life. Options for the horse include sending the horse to a recognized research facility, branding the horse and quarantining it at least 200 yards from other horses for the rest of its life, and euthanizing the horse. Very few quarantine facilities exist, which usually leads to the option of euthanizing the horse. The Florida Research Institute for Equine Nurturing, Development and Safety (a.k.a. F.R.I.E.N.D.S.) is one of the largest such quarantine facilities and is located in south Florida.
The horse industry and the veterinary industry strongly suggest that the risks posed by infected horses, even if they are not showing any clinical signs, are enough of a reason to impose such stringent rules. The precise impacts of the disease on the horse industry are unknown.
Originally, the term referred as sometimes been broadened to encompass "any" communicable or infectious disease. Often the word can only be understood in context, where it is used to emphasise very infectious, easily transmitted, or especially severe communicable disease. They could be very dangerous.
Equine infectious anemia or equine infectious anaemia (EIA), also known by horsemen as swamp fever, is a horse disease caused by a retrovirus and transmitted by bloodsucking insects. The virus ("EIAV") is endemic in the Americas, parts of Europe, the Middle and Far East, Russia, and South Africa. The virus is a lentivirus, like human immunodeficiency virus (HIV). Like HIV, EIA can be transmitted through blood, milk, and body secretions.
Transmission is primarily through biting flies, such as the horse-fly and deer-fly. The virus survives up to 4 hours in the vector (epidemiology). Contaminated surgical equipment and recycled needles and syringes, and bits can transmit the disease. Mares can transmit the disease to their foals via the placenta.
The risk of transmitting the disease is greatest when an infected horse is ill, as the blood levels of the virus are then highest.
Additional neglected tropical diseases include:
Some tropical diseases are very rare, but may occur in sudden epidemics, such as the Ebola hemorrhagic fever, Lassa fever and the Marburg virus. There are hundreds of different tropical diseases which are less known or rarer, but that, nonetheless, have importance for public health.
Feline infectious anemia (FIA) is an infectious disease found in felines, causing anemia and other symptoms. The disease is caused by a variety of infectious agents, most commonly "Mycoplasma haemofelis" (which used to be called "Haemobartonella"). "Haemobartonella" and "Eperythrozoon" species were reclassified as mycoplasmas. Coinfection often occurs with other infectious agents, including: feline leukemia virus (FeLV), feline immunodeficiency virus (FIV), "Ehrlichia" species, "Anaplasma phagocytophilum", and Candidatus "Mycoplasma haemominutum".
Some of the strategies for controlling tropical diseases include:
- Draining wetlands to reduce populations of insects and other vectors, or introducing natural predators of the vectors.
- The application of insecticides and/or insect repellents) to strategic surfaces such as clothing, skin, buildings, insect habitats, and bed nets.
- The use of a mosquito net over a bed (also known as a "bed net") to reduce nighttime transmission, since certain species of tropical mosquitoes feed mainly at night.
- Use of water wells, and/or water filtration, water filters, or water treatment with water tablets to produce drinking water free of parasites.
- Sanitation to prevent transmission through human waste.
- In situations where vectors (such as mosquitoes) have become more numerous as a result of human activity, a careful investigation can provide clues: for example, open dumps can contain stagnant water that encourage disease vectors to breed. Eliminating these dumps can address the problem. An education campaign can yield significant benefits at low cost.
- Development and use of vaccines to promote disease immunity.
- Pharmacologic pre-exposure prophylaxis (to prevent disease before exposure to the environment and/or vector).
- Pharmacologic post-exposure prophylaxis (to prevent disease after exposure to the environment and/or vector).
- Pharmacologic treatment (to treat disease after infection or infestation).
- Assisting with economic development in endemic regions. For example, by providing microloans to enable investments in more efficient and productive agriculture. This in turn can help subsistence farming to become more profitable, and these profits can be used by local populations for disease prevention and treatment, with the added benefit of reducing the poverty rate.
- Hospital for Tropical Diseases
- Tropical medicine
- Infectious disease
- Neglected diseases
- List of epidemics
- Waterborne diseases
- Globalization and disease
Carrion's disease is caused by "Bartonella bacilliformis".
Recent investigations show that "Candidatus Bartonella ancashi" may cause verruga peruana, although it may not meet all of Koch's postulates. There has been no experimental reproduction of the Peruvian wart in animals and there is little research on the disease's natural spread or impact in native animals.
Infectious pancreatic necrosis (IPN) is a severe viral disease of salmonid fish. It is caused by infectious pancreatic necrosis virus, which is a member of the Birnaviridae family. This disease mainly affects young salmonids, such as trout or salmon, of less than six months, although adult fish may carry the virus without showing symptoms. Resistance to infection develops more rapidly in warmer water. It is highly contagious and found worldwide, but some regions have managed to eradicate or greatly reduce the incidence of disease. The disease is normally spread horizontally via infected water, but spread also occurs vertically. It is not a zoonosis.
Currently, no treatment is available.
Good husbandry measures, such as high water quality, low stocking density, and no mixing of batches, help to reduce disease incidence. To eradicate the disease, very strict protocol with regards to movement, water sources and stock replacement must be in place – and still it is difficult to achieve and comes at a high economic cost.
Any age may be affected although it is most common in children aged five to fifteen years. By the time adulthood is reached about half the population will have become immune following infection at some time in their past. Outbreaks can arise especially in nursery schools, preschools, and elementary schools. Infection is an occupational risk for school and day-care personnel. There is no vaccine available for human parvovirus B19, though attempts have been made to develop one.
Because Carrion's disease is often comorbid with "Salmonella" infections, chloramphenicol has historically been the treatment of choice.
Fluoroquinolones (such as ciprofloxacin) or chloramphenicol in adults and chloramphenicol plus beta-lactams in children are the antibiotic regimens of choice during the acute phase of Carrion's disease. Chloramphenicol-resistant "B. bacilliformis" has been observed.
During the eruptive phase, in which chloramphenicol is not useful, azithromycin, erythromycin, and ciprofloxacin have been used successfully for treatment. Rifampin or macrolides are also used to treat both adults and children.
Because of the high rates of comorbid infections and conditions, multiple treatments are often required. These have included the use of corticosteroids for respiratory distress, red blood cell transfusions for anemia, pericardiectomies for pericardial tamponades, and other standard treatments.
Ultraviolet (UV) radiation is implicated in cattle with no pigmentation around the eyelids and cattle with prominently placed eyes. Exudate from the sun-burnt skin around the eyes can contain bacteria and attracts flies. UV light also directly damages the corneal epithelium, leading to a breakdown in host innate immunity.
Dust, dried-up plants, tall vegetation, and oversized or incorrectly placed ear tags may cause mechanical damage to the eye and facilitate bacterial colonization.
The disease may be complicated by concurrent infection with viruses such as infectious bovine rhinotracheitis virus (bovine herpesvirus 1) or adenovirus, bacteria such as "Mycoplasma boviculi" or "Listeria monocytogenes", or infestation by "Thelazia", a nematode.
Vitamin A deficiency is also implicated.
IBK is most prevalent in summer and early autumn.
A recent Meat and Livestock Australia report "estimates that the disease costs Australian beef producers AU$23.5 million annually in lost production and treatment costs".