Coral has a symbiotic relationship with zooxanthellae that provide the coral glucose, glycerol, and amino acids. Under certain water conditions, like fluctuating temperatures and increased nitrogenous waste, corals will appear stressed. Also, these conditions allow for bacteria to grow inside the coral and compete with zooxanthellae. The bacteria produces the characteristic pale yellow lesions and eventually kills the zooxanthellae by impairing its mitosis and its ability to carry out photosynthesis. Yellow-band disease is found on coral reefs in the Caribbean.

Yellow-band disease has severely affected reef building corals in the Caribbean. This disease have been associated with lower coral fecundity, altered tissue composition and a lower activites of antixenobiotic and antioxidant enzymes. Compared to the late 1990s, current data suggests that the disease remains a severe epidemic. In one study, 10 meter belt transects were taken at various depths, sampling coral colonies in the Lesser Antilles. At a depth of 5 m, yellow band rings and lesions were found on 79% of the colonies per transect, and only 21% of the colonies in this depth range appeared healthy.

Recent research indicates that yellow-band disease continues to be in an infectious phases in the Caribbean. It has been

found to cause infection in Pacific coral as well.

Black band disease was first observed on reefs in Belize in 1973 by A. Antonius, who described the pathogen he found infecting corals as "Oscillatoria membranacea", one of the cyanobacteria. The band color may be blackish brown to red depending on the vertical position of a cyanobacterial population associated with the band. The vertical position is based on a light intensity-dependent photic response of the cyanobacterial filaments, and the color (due to the cyanobacterial pigment phycoerythrin) is dependent on the thickness of the band. The band is approximately thick and ranges in width from to White specks may be present on surface, at times forming dense white patches. The pathogenic microbial mat moves across coral colonies at rates from to a day. Tissue death is caused by exposure to an hypoxic, sulfide-rich microenvironment associated with the base of the band.

Black band disease is a coral disease in which corals develop a black band. It is characterized by complete tissue degradation due to a pathogenic microbial consortium. The mat is present between apparently healthy coral tissue and freshly exposed coral skeleton.

White band disease (Acroporid white syndrome) is a coral disease that affects acroporid corals and is distinguishable by the white band of dead coral tissue that it forms. The disease completely destroys the coral tissue of Caribbean acroporid corals, specifically elkhorn coral ("Acropora palmata") and staghorn coral ("A. cervicornis"). The disease exhibits a pronounced division between the remaining coral tissue and the exposed coral skeleton. These symptoms are similar to white plague, except that white band disease is only found on acroporid corals, and white plague has not been found on any acroporid corals. It is part of a class of similar disease known as "white syndromes", many of which may be linked to species of "Vibrio" bacteria. While the pathogen for this disease has not been identified, "Vibrio carchariae" may be one of its factors. The degradation of coral tissue usually begins at the base of the coral, working its way up to the branch tips, but it can begin in the middle of a branch.

Coral diseases, comprising the diseases that affect corals, injure the living tissues and often result in the death of part or the whole of the colony. These diseases have been occurring more frequently in the twenty-first century as conditions become more stressful for many shallow-water corals. The pathogens causing the diseases include bacteria, fungi and protozoa, but it is not always possible to identify the pathogen involved.

Muscardine is a disease of insects. It is caused by many species of entomopathogenic fungus. Many muscardines are known for affecting silkworms. Muscardine may also be called calcino.

While studying muscardine in silkworms in the 19th century, Agostino Bassi found that the causal agent was a fungus. This was the first demonstration of the germ theory of disease, the first time a microorganism was recognized as an animal pathogen.

There are many types of muscardine. They are often named for the color of the conidial layer each fungus leaves on its host.

Coconut Cadang Cadang Viroid (CCCVd) can be confused with another viroid called Coconut Tinangaja Viroid (CTiVd). That is because both viroids have 64% of their sequence of nucleotides in common. They both affect coconut palm, and infected plants have similar symptoms: spots on the leaves reduced top, yellow palms and even death.

There are few differences between both viroids in the effects caused on fruit: CTiVd causes small nuts, while CCCVd causes round and reduced nuts. Moreover, CTiVd has 254 nucleotides of length, while CCCVd has 246.

Corals growing in the Caribbean Sea are particularly affected by disease, perhaps because of the limited water circulation and the density of the human population on the surrounding land masses. Disease is also present in the tropical Indo-Pacific, but it is not so widespread, perhaps because of the more dispersed locations of the reefs.

Wheat yellow rust ("Puccinia striiformis" f.sp. "tritici"), also known as stripe rust, is one of the three wheat rust diseases principally found in wheat grown in cooler environments. Such locations are generally associated with northern latitudes or cooler seasons.

Fungicidal agents such as azadirachtin and phytoallexin have been used against some muscardine pathogens. Silkworm breeders dust their cages with slaked lime to discourage fungal growth. In India a dust of chaff soaked in formalin is applied to the larvae.

Coconut cadang-cadang disease has no treatment yet. However, chemotherapy with antibiotics has been tried with tetracycline solutions; antibiotics failed trying to alter progress of the disease since they had no significant effect on any of the studied parameters. When the treated plants were at the early stage, tetracycline injections failed to prevent the progression of the palms to more advanced stages, nor did they affect significantly the mean number of spathes or nuts. Penicillin treatment had no apparent improvement either.

Control strategies are elimination of reservoir species, vector control, mild strain protection and breeding for host resistance. Eradication of diseased plants is usually performed to minimize spread but is of dubious efficacy due to the difficulties of early diagnosis as the virus etiology remains unknown and the one discovered are the three main stages in the disease development.

Skeletal eroding band (SEB) is a disease of corals that appears as a black or dark gray band that slowly advances over corals, leaving a spotted region of dead coral in its wake. It is the most common disease of corals in the Indian and Pacific Oceans, and is also found in the Red Sea.

So far one agent has been clearly identified, the ciliate "Halofolliculina corallasia". This makes SEB the first coral disease known to be caused by a protozoan. When "H. corallasia" divides, the daughter cells move to the leading edge of the dark band and produce a protective shell called a lorica. To do this, they drill into the coral's limestone skeleton, killing coral polyps in the process.

A disease with very similar symptoms has been found in the Caribbean Sea, but has been given a different name as it is caused by a different species in the genus "Halofolliculina" and occurs in a different type of environment.

Necrotic ring spot is a common disease of turf caused by soil borne fungi (Ophiosphaerella korrae) that mainly infects roots (4). It is an important disease as it destroys the appearance of turfgrasses on park, playing fields and golf courses. Necrotic Ring Spot is caused by a fungal pathogen that is an ascomycete that produces ascospores in an ascocarp (6). They survive over winter, or any unfavorable condition as sclerotia. Most infection occurs in spring and fall when the temperature is about 13 to 28°C (5). The primary hosts of this disease are cool-season grasses such as Kentucky bluegrass and annual bluegrass (6). Once turf is infected with "O. korrae", it kills turf roots and crowns. Symptoms of the disease are quite noticeable since they appear as large yellow ring-shaped patches of dead turf. Management of the disease is often uneasy and requires application of multiple controls. The disease can be controlled by many different kind of controls including chemicals and cultural.

White band disease causes the affected coral tissue to decorticate off the skeleton in a white uniform band for which the disease was given its name. The band, which can range from a few millimeters to 10 centimeters wide, typically works its way from the base of the coral colony up to the coral branch tips. The band progresses up the coral branch at an approximate rate of 5 millimeters per day, causing tissue loss as it works its way to the branch tips. After the tissue is lost, the bare skeleton of the coral may later by colonized by filamentous algae.

There are two variants of white band disease, type I and type II. In Type I of white band disease, the tissue remaining on the coral branch shows no sign of coral bleaching, although the affected colony may appear lighter in color overall. However, a variant of white band disease, known simply as white band disease Type II, which was found on Staghorn colonies near the Bahamas, does produce a margin of bleached tissue before it is lost. Type II of white band disease can be mistaken for coral bleaching. By examining the remaining living coral tissue for bleaching, one can delineate which type of the disease affects a given coral.

Necrotic ring spot can be managed through chemical and cultural controls. Cultural control includes the use of ammonium sulfate or other acidifying fertilizers to suppress the pathogen by lowering the pH of the soil to between 6.0 and 6.2. The more acidic soil discourages the activity of "O. korrae" (9) When reducing pH to these levels, additional manganese applications should be undertaken to compensate for lower pH. As of now, there are only two resistant cultivars of bluegrass, which are ‘Riviera’, and ‘Patriot’ (9). One component of their resistance could be that they are tolerant to low temperature, because the grass is more susceptible to the pathogen under colder temperatures(8). In addition, reducing watering inputs and growing turf on well drained soils can lessen disease symptoms.

Many different fungicides are used to control the pathogen, Fenarimol, Propiconazole, Myclobutanil, and Azoxystrobin (8). Historically, Fenarimol and Myclobutanil were predominantly used (14). In a study where diluted pesticides were sprayed throughout infested test plots, Fenarimol was found to be the most effective with a 94.6% reduction of the disease. Myclobutanil also decreased the amount of disease, but only by 37.7% (8). Myclobutanil is generally recognized as a very weakly acting demethylation inhibitor (DMI) fungicide and fenarimol is no longer registered for turf so a number of other DMI fungicides have been employed successfully, including Propiconazole, Tebuconazole, Metconazole and others. Pyraclostrobin and Fluoxastrobin have also been used to control the pathogen.

"Yellow rust" takes its name from the appearance of yellow-colored stripes produced parallel along the venations of each leaf blade. These yellow stripes are actually characteristic of uredinia that produce yellow colored urediniospores. Primary hosts of yellow rust are "Triticum aestivum" (bread wheat), "Triticum turgidum" (durum wheat), triticale, and a few "Hordeum vulgare" (barley) cultivars. The alternate host was discovered by accident in 2010. Species of common barberry plants (the alternate host of wheat stem rust) were found harbouring stripe rust. When transferred to grass hosts, Kentucky Bluegrass was successfully infected and urediniospores were produced. Several species of Berberis were then investigated as alternate hosts of Wheat stripe rust and inoculations were successful.

The disease usually occurs early in the growth season, when temperature ranges between 2 and 15 °C; but it may occur to a maximum of 23 °C. High humidity and rainfall are favorable conditions for increasing the infection on both leaf blade and leaf sheath, even on spikes when in epidemic form. Symptoms are stunted and weakened plants, shriveled grains, fewer spikes, loss in number of grains per spike and grain weight. Losses can be 50%, but in severe situations 100% is vulnerable. In countries where wheat is grown in winters or at high elevations, yellow rust is a common threat, but not more significant than wheat leaf rust and stem rust, which are continuous threats in all wheat-growing countries.

Skeletal eroding band is visible as a black or dark gray band that slowly advances over corals, leaving a spotted region of dead coral in its wake. The spotted area distinguishes skeletal eroding band from black band disease, which also forms an advancing black band but leaves a completely white dead area behind it.

Skeletal eroding band was first noticed in 1988 near Papua New Guinea and then near Lizard Island in Australia's Great Barrier Reef, but was regarded as a gray variant of black band disease, as were instances off Mauritius in 1990. Surveys in 1994 in and around the Red Sea first identified the condition as a unique disease. It is now considered the commonest disease of corals in the Indian and Pacific Oceans, especially in warmer or more polluted waters.

The spread of the disease across an infected coral has been measured at in the Red Sea and around the Great Barrier Reef. Corals of the families Acroporidae and Pocilloporidae are the most vulnerable to infection. A study in 2008 found that the infection spread at about per day in colonies of "Acropora muricata", eventually wiping out 95% of its victims. However, experiments showed that the disease easily spread to already dead and dying areas of corals but did not attack undamaged corals.

The disease is endemic in tropical and subtropical regions. The exact incidence and geographical distribution of mycetoma throughout the world is not known as the disease is usually painless, slowly progressive and presented to health centres only in late stages by majority of patients. Mycetoma has an uneven worldwide distribution.

Favid (of "favus" Latin for "honeycomb" or tinea favosa) is a disease usually affecting the scalp, but occurring occasionally on any part of the skin, and even at times on mucous membranes.

The word “Favid” is more used than French word “favus”, which is close to the Latin etymology.

Mycetoma may be caused by bacteria from the phylum Actinomycetes, or by fungi (Eumycetes) where it is called Eumycetoma. Bacterial and fungal species that can cause mycetoma are listed below under their characteristic colours of discharge from infected wounds:

Red discharge

- "Actinomadura pelletieri"

White or Yellow discharge

- "Acremonium strictum"

- "Actinomadura madurae"

- "Aspergillus nidulans"

- "Noetestudina rosatii"

- "Phaeoacremonium krajdenii"

- "Pseudallescheria boydii"

Black discharge

- "Aspergillus terreus"

- "Curvularia lunata"

- "Cladophialophora bantiana"

- "Exophiala jeanselmei"

- "Leptosphaeria senegalensis"

- "Leptosphaeria tompkinsii"

- "Madurella grisea"

- "Madurella mycetomatis"

- "Pyrenochaeta romeroi"

Some species of the bacterial genus "Nocardia" (including "Nocardia asteroides" and "Nocardia brasiliensis") which can cause mycetoma produce a yellow coloured discharge, and those of the bacterial genus "Streptomyces" (including "Streptomyces somaliensis") produce an yellow or red coloured discharge.

Up until the advent of modern therapies, favid was widespread worldwide; prior to Schönlein's recognition of it as a fungal disease, it was frequently confused with Hansen's disease, better known as leprosy, and European sufferers were sometimes committed to leprosaria. Today, due to this species' high susceptibility to the antifungal drug griseofulvin, it has been eliminated from most parts of the world except rural central Asia and scattered rural areas of Africa. It is mainly a disease connected to demographic poverty and isolation, but is so readily treatable that it is among the diseases most likely to be completely eliminated by modern medicine.

Diphtheritic stomatitis is a recently discovered disease and has thus far been reported only in Yellow-eyed penguins ("Megadyptes antipodes"). Its symptoms are similar to human diphtheria and is characterized by infecteous lesions in the mouth area that impede swallowing and cause respiratory troubles. The infection is caused by "Corynebacterium amycolatum", an aerobic Gram-positive bacterium and mainly affects very young chicks. However, it seems likely that a triggering agent (e.g. a virus) might be involved in which renders the corynebacterium a secondary pathogen.

The disease has been a serious cause of mortality in the 2002 and 2004 Yellow-eyed penguin breeding seasons. It seems that only the New Zealand South Island and Stewart Island/Rakiura were affected.

During the latest outbreak of the disease (2004), several treatment methods were tested. Main treatment involved the administration of antibiotics, in some cases glucose solution or dietary mixtures were additionally supplemented. Outcome of the different treatment methods varied greatly. Especially the success of antibiotic treatment and a widespread use on wild animals remains a matter of debate.

Xanthochromism (also called xanthochroism or xanthism) is an unusually yellow pigmentation in an animal. It is often associated with the lack of usual red pigmentation and its replacement with yellow. The cause is usually genetic but may also be related to the animal's diet. A Cornell University survey of unusual-looking birds visiting feeders reported that 4% of such birds were described as xanthochromistic (compared with 76% albinistic). The opposite of xanthochromism, a deficiency in or complete absence of yellow pigment, is known as "axanthism".

Birds exhibiting genetic xanthochromism, especially deliberately bred mutations of several species of parrot in aviculture, are termed "lutinos". Wild birds in which xanthochromism has been recorded include yellow wagtail, wood warbler, Cape May warbler, rose-breasted grosbeak, evening grosbeak, red-bellied woodpecker, scarlet tanager, northern cardinal, great spotted woodpecker, common tailorbird, crimson-breasted shrike, kākāriki and kea.