How myiasis affects the human body depends on where the larvae are located. Larvae may infect dead, necrotic (prematurely dying) or living tissue in various sites: the skin, eyes, ears, stomach and intestinal tract, or in genitourinary sites. They may invade open wounds and lesions or unbroken skin. Some enter the body through the nose or ears. Larvae or eggs can reach the stomach or intestines if they are swallowed with food and cause gastric or intestinal myiasis.

Several different presentations of myiasis and their symptoms:

Nosocomial myiasis is myiasis acquired in a hospital setting. It is quite frequent, as patients with open wounds or sores can be infested if flies are present. To prevent nosocomial myiasis, hospital rooms must be kept free of flies.

Fly strike in sheep is a condition where parasitic flies lay eggs on soiled wool or open wounds. After hatching, the maggots, bury themselves in the sheep’s wool and eventually under the sheep’s skin, feeding off their flesh. Once the larvae develop, flies continue to deposit eggs on to new or already infected sheep, starting the infection process over again. Sheep display symptoms such as agitation, odour and matted wool, all which further encourage the attraction of flies. Fly strike can be lethal for sheep due to ammonia poisoning.

Fly strike is problematic, not only causing loss or degradation of stock, but also requiring expenditure of both money and time for effective management. In Australia, "Lucilia cuprina" causes about 90% of infestations, and "Chrysomya rufifacies" is the most common secondary pest the targets wounds caused by "L. cuprina".

Flystrike in sheep is a myiasis condition, in which domestic sheep are infected by one of several species of flies which are external parasites of sheep.

The most common symptom of all snakebites is overwhelming fear, which contributes to other symptoms, including nausea and vomiting, diarrhea, vertigo, fainting, tachycardia, and cold, clammy skin. Television, literature, and folklore are in part responsible for the hype surrounding snakebites, and people may have unwarranted thoughts of imminent death.

Dry snakebites and those inflicted by a non-venomous species can still cause severe injury. There are several reasons for this: a snakebite may become infected, with the snake's saliva and fangs sometimes harboring pathogenic microbial organisms, including "Clostridium tetani". Infection is often reported with viper bites whose fangs are capable of deep puncture wounds. Bites may cause anaphylaxis in certain people.

Most snakebites, whether by a venomous snake or not, will have some type of local effect. There is minor pain and redness in over 90 percent of cases, although this varies depending on the site. Bites by vipers and some cobras may be extremely painful, with the local tissue sometimes becoming tender and severely swollen within five minutes. This area may also bleed and blister and can eventually lead to tissue necrosis. Other common initial symptoms of pit viper and viper bites include lethargy, bleeding, weakness, nausea, and vomiting. Symptoms may become more life-threatening over time, developing into hypotension, tachypnea, severe tachycardia, severe internal bleeding, altered sensorium, kidney failure, and respiratory failure.

Bites caused by some snakes, such as the kraits, coral snake, Mojave rattlesnake, and the speckled rattlesnake, reportedly cause little or no pain despite being serious potentially life-threatening injuries. Those bitten may also describe a "rubbery", "minty", or "metallic" taste if bitten by certain species of rattlesnake. Spitting cobras and rinkhalses can spit venom in a person's eyes. This results in immediate pain, ophthalmoparesis, and sometimes blindness.

Some Australian elapids and most viper envenomations will cause coagulopathy, sometimes so severe that a person may bleed spontaneously from the mouth, nose, and even old, seemingly healed wounds. Internal organs may bleed, including the brain and intestines and will cause ecchymosis (bruising) of the skin.

Venom emitted from elapids, including sea snakes, kraits, cobras, king cobra, mambas, and many Australian species, contain toxins which attack the nervous system, causing neurotoxicity. The person may present with strange disturbances to their vision, including blurriness. Paresthesia throughout the body, as well as difficulty in speaking and breathing, may be reported. Nervous system problems will cause a huge array of symptoms, and those provided here are not exhaustive. If not treated immediately they may die from respiratory failure.

Venom emitted from some types of cobras, almost all vipers and some sea snakes causes necrosis of muscle tissue. Muscle tissue will begin to die throughout the body, a condition known as rhabdomyolysis. Rhabdomyolysis can result in damage to the kidneys as a result of myoglobin accumulation in the renal tubules. This, coupled with hypotension, can lead to acute renal failure, and, if left untreated, eventually death.

A snakebite is an injury caused by the bite of a snake, especially a venomous snake. A common symptom of a bite from a venomous snake is the presence of two puncture wounds from the animal's fangs. Sometimes venom injection from the bite may occur. This may result in redness, swelling, and severe pain at the area, which may take up to an hour to appear. Vomiting, trouble seeing, tingling of the limbs, and sweating may result. Most bites are on the hands or arms. Fear following a bite is common with symptoms of a racing heart and feeling faint. The venom may cause bleeding, kidney failure, a severe allergic reaction, tissue death around the bite, or breathing problems. Bites may result in the loss of a limb or other chronic problems. The outcome depends on the type of snake, the area of the body bitten, the amount of venom injected, and the health conditions of the person. Problems are often more severe in children than adults, due to their smaller size.

Snakes bite both as a method of hunting and as a means of protection. Risk factors for bites include working outside with one's hands such as in farming, forestry, and construction. Snakes commonly involved in poisonings include elapids (such as kraits, cobras and mambas), vipers, and sea snakes. The majority of snake species do not have venom and kill their prey by squeezing them. Venomous snakes can be found on every continent except Antarctica. Determining the type of snake that caused a bite is often not possible. The World Health Organization says snakebites are a "neglected public health issue in many tropical and subtropical countries".

Prevention of snake bites can involve wearing protective footwear, avoiding areas where snakes live, and not handling snakes. Treatment partly depends on the type of snake. Washing the wound with soap and water and holding the limb still is recommended. Trying to suck out the venom, cutting the wound with a knife, or using a tourniquet is not recommended. Antivenom is effective at preventing death from bites; however, antivenoms frequently have side effects. The type of antivenom needed depends on the type of snake involved. When the type of snake is unknown, antivenom is often given based on the types known to be in the area. In some areas of the world getting the right type of antivenom is difficult and this partly contributes to why they sometimes do not work. An additional issue is the cost of these medications. Antivenom has little effect on the area around the bite itself. Supporting the person's breathing is sometimes also required.

The number of venomous snakebites that occur each year may be as high as five million. They result in about 2.5 million poisonings and 20,000 to 125,000 deaths. The frequency and severity of bites vary greatly among different parts of the world. They occur most commonly in Africa, Asia, and Latin America, with rural areas more greatly affected. Deaths are relatively rare in Australia, Europe and North America. For example, in the United States, about seven to eight thousand people per year are bitten by venomous snakes (about one in 40 thousand people) and about five people die (about one death per 65 million people).

Leeches are segmented worms that belong to the phylum Annelida and comprise the subclass Hirudinea. Like the oligochaetes, such as earthworms, leeches share a clitellum and are hermaphrodites. Nevertheless, they differ from the oligochaetes in significant ways. For example, leeches do not have bristles and the external segmentation of their bodies does not correspond with the internal segmentation of their organs. Their bodies are much more solid as the spaces in their coelom are dense with connective tissues. They also have two suckers, one at each end.

The majority of leeches live in freshwater environments, while some species can be found in terrestrial and marine environments. The best-known leeches, such as the medicinal leech, "Hirudo medicinalis", are hematophagous, feeding on vertebrate blood and invertebrate hemolymph. Most leech species, however, are predatory, feeding primarily by swallowing other invertebrates.

Almost 700 species of leeches are currently recognized, of which some 100 are marine, 90 terrestrial and the remainder freshwater taxa.

Leeches, such as the "Hirudo medicinalis", have been historically used in medicine to remove blood from patients. The practice of leeching can be traced to ancient India and Greece, and continued well into the 18th and 19th centuries in both Europe and North America. In modern times, leeches are used medically in procedures such as the reattachment of body parts and reconstructive and plastic surgeries and, in Germany, treating osteoarthritis.

The characteristics of a burn depend upon its depth. Superficial burns cause pain lasting two or three days, followed by peeling of the skin over the next few days. Individuals suffering from more severe burns may indicate discomfort or complain of feeling pressure rather than pain. Full-thickness burns may be entirely insensitive to light touch or puncture. While superficial burns are typically red in color, severe burns may be pink, white or black. Burns around the mouth or singed hair inside the nose may indicate that burns to the airways have occurred, but these findings are not definitive. More worrisome signs include: shortness of breath, hoarseness, and stridor or wheezing. Itchiness is common during the healing process, occurring in up to 90% of adults and nearly all children. Numbness or tingling may persist for a prolonged period of time after an electrical injury. Burns may also produce emotional and psychological distress.

One recommended method of removal is using a fingernail or other flat, blunt object to break the seal of the oral sucker at the anterior end of the leech, repeating with the posterior end, then flicking the leech away. As the fingernail is pushed along the person's skin against the leech, the suction of the sucker's seal is broken, at which point the leech will detach its jaws.

Common, but medically inadvisable, techniques to remove a leech are to apply a flame, a lit cigarette, salt, soap, or a chemical such as alcohol, vinegar, lemon juice, insect repellent, heat rub, or certain carbonated drinks. These will cause the leech to quickly detach; however, it will also regurgitate its stomach contents into the wound. The vomit may carry disease, and thus increase the risk of infection.

An externally attached leech will detach and fall off on its own when it is satiated on blood, which may be anywhere from 20 minutes to two hours or more. After feeding, the leech will detach and depart. Internal attachments, such as inside the nasal passage or vaginal attachments, are more likely to require medical intervention.

After removal or detachment, the wound should be cleaned with soap and water, and bandaged. Bleeding may continue for some time, due to the leech's hirudin. Bleeding time will vary, with location, from a few hours to three days. This is a function of the hirudin and other compounds that reduce the surface tension of the blood. Anticlotting medications also affect the bleeding time. Applying pressure can reduce bleeding, although blood loss from a single bite is not dangerous. The wound normally itches as it heals, but should not be scratched, as this may complicate healing and introduce other infections. An antihistamine can reduce itching, and applying a cold pack can reduce pain or swelling.

Some people have severe allergic or anaphylactic reactions from leech bites and require urgent medical care. Symptoms include red blotches or an itchy rash over the body, swelling around the lips or eyes, feeling faint or dizzy, and difficulty breathing.

A burn is a type of injury to skin, or other tissues, caused by heat, cold, electricity, chemicals, friction, or radiation. Most burns are due to heat from hot liquids, solids, or fire. While rates are similar for males and females the underlying causes often differ. Among women in some areas, risk is related to use of open cooking fires or unsafe cook stoves. Among men, risk is related to the work environments. Alcoholism and smoking are other risk factors. Burns can also occur as a result of self harm or violence between people.

Burns that affect only the superficial skin layers are known as superficial or first-degree burns. They appear red without blisters and pain typically lasts around three days. When the injury extends into some of the underlying skin layer, it is a partial-thickness or second-degree burn. Blisters are frequently present and they are often very painful. Healing can require up to eight weeks and scarring may occur. In a full-thickness or third-degree burn, the injury extends to all layers of the skin. Often there is no pain and the burn area is stiff. Healing typically does not occur on its own. A fourth-degree burn additionally involves injury to deeper tissues, such as muscle, tendons, or bone. The burn is often black and frequently leads to loss of the burned part.

Burns are generally preventable. Treatment depends on the severity of the burn. Superficial burns may be managed with little more than simple pain medication, while major burns may require prolonged treatment in specialized burn centers. Cooling with tap water may help pain and decrease damage; however, prolonged cooling may result in low body temperature. Partial-thickness burns may require cleaning with soap and water, followed by dressings. It is not clear how to manage blisters, but it is probably reasonable to leave them intact if small and drain them if large. Full-thickness burns usually require surgical treatments, such as skin grafting. Extensive burns often require large amounts of intravenous fluid, due to capillary fluid leakage and tissue swelling. The most common complications of burns involve infection. Tetanus toxoid should be given if not up to date.

In 2015, fire and heat resulted in 67 million injuries. This resulted in about 2.9 million hospitalizations and 176,000 deaths. Most deaths due to burns occur in the developing world, particularly in Southeast Asia. While large burns can be fatal, treatments developed since 1960 have improved outcomes, especially in children and young adults. In the United States, approximately 96% of those admitted to a burn center survive their injuries. The long-term outcome is related to the size of burn and the age of the person affected.

Phossy jaw, formally phosphorus necrosis of the jaw, is an occupational disease of those who work with white phosphorus, also known as "yellow phosphorus", without proper safeguards. It was most commonly seen in workers in the match-stick industry in the 19th and early 20th century. Modern occupational hygiene practices have eliminated the working conditions which caused this disease. This disease is caused by the vapour of white phosphorus, which destroys the bones of the jaw.

Those with phossy jaw would usually begin suffering painful toothaches and swelling of the gums. Over time, the jaw bone began to abscess. Affected bones glowed a greenish-white colour in the dark. The condition also caused serious brain damage. Surgical removal of the afflicted jaw bones could save the patient; otherwise, death from organ failure would follow. The disease was extremely painful and disfiguring to the patient, with dying bone tissue rotting away accompanied by a foul-smelling discharge. However, removal of the jaw bone had serious effects on patients' ability to eat, leading to further health concerns including malnutrition.

As is common with specific phobias, an occasional fright may give rise to abnormal anxiety that requires treatment. An abnormal fear of bats may be treated by any standard treatment for specific phobias. Due to the fact that the fear is not life altering, it can usually just be left untreated.

Fear of bats, sometimes called chiroptophobia (from the Greek χείρ - "cheir", "hand" and πτερόν - "pteron", "wing" referring to the order of the bats, and φόβος - "phobos", meaning "fear"), is a specific phobia associated with bats and to common negative stereotypes and fear of bats.

Symptoms of iron deficiency can occur even before the condition has progressed to iron deficiency anemia.

Symptoms of iron deficiency are not unique to iron deficiency (i.e. not pathognomonic). Iron is needed for many enzymes to function normally, so a wide range of symptoms may eventually emerge, either as the secondary result of the anemia, or as other primary results of iron deficiency. Symptoms of iron deficiency include:

- fatigue

- dizziness/lightheadedness

- pallor

- hair loss

- twitches

- irritability

- weakness

- pica

- brittle or grooved nails

- hair thinning

- Plummer–Vinson syndrome: painful atrophy of the mucous membrane covering the tongue, the pharynx and the esophagus

- impaired immune function

- pagophagia

- restless legs syndrome

Continued iron deficiency may progress to anaemia and worsening fatigue. Thrombocytosis, or an elevated platelet count, can also result. A lack of sufficient iron levels in the blood is a reason that some people cannot donate blood.

Animal hoarding is keeping a higher-than-usual number of animals as domestic pets without ability to properly house or care for them, while at the same time denying this inability. Compulsive hoarding can be characterized as a symptom of mental disorder rather than deliberate cruelty towards animals. Hoarders are deeply attached to their pets and find it extremely difficult to let the pets go. They typically cannot comprehend that they are harming their pets by failing to provide them with proper care. Hoarders tend to believe that they provide the right amount of care for them. The American Society for the Prevention of Cruelty to Animals provides a "Hoarding Prevention Team", which works with hoarders to help them attain a manageable and healthy number of pets.

Iron deficiency happens when a body has not enough (or not qualitatively enough) iron to supply its eventual needs. Iron is present in all cells in the human body and has several vital functions, such as: carrying oxygen to the tissues from the lungs as a key component of the hemoglobin protein; acting as a transport medium for electrons within the cells in the form of cytochromes; facilitating oxygen enzyme reactions in various tissues. Too little iron can interfere with these vital functions and lead to morbidity and death.

Total body iron averages approximately 3.8 g in men and 2.3 g in women. In blood plasma, iron is carried tightly bound to the protein transferrin. There are several mechanisms that control human iron metabolism and safeguard against iron deficiency. The main regulatory mechanism is situated in the gastrointestinal tract. When loss of iron is not sufficiently compensated by adequate intake of iron from the diet, a state of iron deficiency develops over time. When this state is uncorrected, it leads to iron deficiency anemia. Before anemia occurs, the medical condition of iron deficiency without anemia is called latent iron deficiency (LID) or Iron-deficient erythropoiesis (IDE).

Untreated iron deficiency can lead to iron deficiency anemia, a common type of anemia. Anemia is a condition characterized by inadequate red blood cells (erythrocytes) or hemoglobin. Iron deficiency anemia occurs when the body lacks sufficient amounts of iron, resulting in reduced production of the protein hemoglobin. Hemoglobin binds to oxygen, thus enabling red blood cells to supply oxygenated blood throughout the body. Children, pre-menopausal women (women of child-bearing age) and people with poor diet are most susceptible to the disease. Most cases of iron deficiency anemia are mild, but if not treated can cause problems like fast or irregular heartbeat, complications during pregnancy, and delayed growth in infants and children.

Symptoms may include fever and headache, but the distinguishing characteristic of this disease is attacks of severe pain in the lower chest, often on one side. The slightest movement of the rib cage causes a sharp increase of pain, which makes it very difficult to breathe, and an attack is therefore quite a frightening experience, although it generally passes off before any actual harm occurs. The attacks are unpredictable and strike "out of the blue" with a feeling like an iron grip around the rib cage. The colloquial names for the disease, such as 'The Devil's grip' (see also "other names" below) reflect this symptom.

This inherited disease is characterized by violent muscle twitching and substantial muscle weakness or paralysis among affected horses. HYPP is a dominant genetic disorder; therefore, heterozygotes bred to genotypically normal horses have a statistic probability of producing clinically affected offspring 50% of the time.

Horses with HYPP can be treated with some possibility of reducing clinical signs, but the degree that medical treatment helps varies from horse to horse. There is no cure. Horses with HYPP often lose muscle control during an attack.

Some horses are more affected by the disease than others and some attacks will be more severe than others, even in the same horse. Symptoms of an HYPP attack may include:

- Muscle trembling

- Prolapse of the third eyelid — this means that the third eyelid flickers across the eye or covers more of the eye than normal

- Generalized weakness

- Weakness in the hind end — the horse may look as though it is 'dog-sitting'

- Complete collapse

- Abnormal whinny — because the muscles of the voicebox are affected as well as other muscles

- Death — in a severe attack the diaphragm is paralyzed and the horse can suffocate

HYPP attacks occur randomly and can strike a horse standing calmly in a stable just as easily as during exercise. Following an HYPP attack, the horse appears normal and is not in any pain which helps to distinguish it from Equine Exertional Rhabdomyolysis (ER), commonly known as "Azoturia," "Monday Morning Sickness" or "tying up." Horses that are tying up usually suffer attacks in connection with exercise and may take anywhere from 12 hours to several days to recover. Muscle tissue is damaged in an attack of ER, and the horse will be in pain during and following an attack. A blood test will reveal elevations in certain muscle enzymes after an episode of ER and so the two diseases, while superficially similar, are easily distinguished from one another in the laboratory.

Unlike with seizures, horses with HYPP are fully conscious and lucid during an attack. Horses may suffocate during an HYPP attack due to paralysis of the respiratory system. Horses that collapse during an episode are clearly distressed as they repeatedly struggle to get to their feet. If this occurs while the horse is being ridden or otherwise handled, the human handler or rider may be at risk of being injured by the movement of the horse.

Neonatal tetanus is a form of generalised tetanus that occurs in newborns. Infants who have not acquired passive immunity from the mother having been immunised are at risk. It usually occurs through infection of the unhealed umbilical stump, particularly when the stump is cut with a non-sterile instrument. Neonatal tetanus mostly occurs in developing countries, particularly those with the least developed health infrastructure. It is rare in developed countries.

Endocardial fibroelastosis (EFE) is a rare heart disorder usually occurring in children two years old and younger. It may also be considered a reaction to stress, not necessarily a specific disease.

It should not be confused with endomyocardial fibrosis.

Melancholia (from , '), also lugubriousness, from the Latin "lugere", to mourn; moroseness, from the Latin "morosus", self-willed, fastidious habit; wistfulness, from old English "wist": intent, or saturnine, was a concept in ancient and pre-modern medicine. Melancholy was one of the four temperaments matching the four humours. In the 19th century, "melancholia" could be physical as well as mental, and melancholic conditions were classified as such by their common cause rather than by their properties.

In neonatal tetanus, symptoms usually appear from 4 to 14 days after birth, averaging about 7 days. The fatality rate for infants has been estimated as 70% to 100%; death usually occurs by the age of 2 weeks. On the basis of clinical findings, four different forms of tetanus have been described. The time from exposure to symptoms may be up to several months.

The illness lasts about a week and is rarely fatal. Treatment includes the administration of nonsteroidal anti-inflammatory agents or the application of heat to the affected muscles. Relapses during the weeks following the initial episode are a characteristic feature of this disease.

Hyperkalemic periodic paralysis (HYPP, HyperKPP) is a genetic disorder. It occurs in humans, horses (where it is also known as Impressive syndrome, after an index case in a horse named Impressive, or possibly one of his ancestors), and perhaps other animals. It is an inherited autosomal dominant disorder that affects sodium channels in muscle cells and the ability to regulate potassium levels in the blood. It is most commonly associated with horses, but occurs in humans, where it may be called Gamstorp episodic adynamy. It is characterized by muscle hyperexcitability or weakness which, exacerbated by potassium, heat or cold, can lead to uncontrolled shaking followed by paralysis. Onset in humans usually occurs in early childhood, but still occurs with adults.

The mutation which causes this disorder is dominant on SCN4A with linkage to the sodium channel expressed in muscle. The mutation causes single amino acid changes in parts of the channel which are important for inactivation. In the presence of high potassium levels, including those induced by diet, sodium channels fail to inactivate properly.

Equine hyperkalemic periodic paralysis occurs in 1 in 50 Quarter Horses and can be traced to a single ancestor, a stallion named Impressive.