The hypothesis that pesticide use has contributed to declining amphibian populations has been suggested several times in the literature. Interactions between pesticides and chytridiomycosis were examined in 2007, and sublethal exposure to the pesticide carbaryl (a cholinesterase inhibitor) was shown to increase susceptibility of foothill yellow-legged frogs ("Rana boylii") to chytridiomycosis. In particular, the skin peptide defenses were significantly reduced after exposure to carbaryl, suggesting pesticides may inhibit this innate immune defence, and increase susceptibility to disease.

Chytridiomycosis is an infectious disease in amphibians, caused by the chytrid "Batrachochytrium dendrobatidis", a nonhyphal zoosporic fungus. Chytridiomycosis has been linked to dramatic population declines or even extinctions of amphibian species in western North America, Central America, South America, eastern Australia, East Africa (Tanzania) and Dominica and Montserrat in the Caribbean. Much of the New World is also at risk of the disease arriving within the coming years.

The fungus is capable of causing sporadic deaths in some amphibian populations and 100% mortality in others. No effective measure is known for control of the disease in wild populations. Various clinical signs are seen by individuals affected by the disease. A number of options are possible for controlling this disease-causing fungus, though none has proved to be feasible on a large scale. The disease has been proposed as a contributing factor to a global decline in amphibian populations that apparently has affected about 30% of the amphibian species of the world.

Although the exact cause of feline acne is unknown, some causes include:

- Hyperactive sebaceous glands

- Poor hygiene

- Stress

- Developing secondary to fungal, viral, and bacterial infections

- Reaction to medication

- Drinking from plastic containers to which the cat is allergic

- Demodicosis or mange, causing itchiness and hair loss

- Suppressed immune system

- Hair follicles that don't function properly

- Rubbing the chin (to display affection or mark territory) on non-sanitized household items

- Hormonal imbalance

- Contracting the infection from other cats in the same household

Due to the high number of hosts, eradication of tungiasis is not feasible, at least not easily so. Public health and prevention strategies should then be done with elimination as the target. Better household hygiene, including having a cemented rather than a sand floor, and washing it often, would lower the rates of tungiasis significantly.

Though vaccines would be useful, due to the ectoparasitic nature of chigoe flea, they are neither a feasible nor an effective tool against tungiasis. Nevertheless, due to the high incidence of secondary infection, those at risk of tungiasis should get vaccinated against tetanus. A better approach is to use repellents that specifically target the chigoe flea. One very successful repellent is called Zanzarin, a derivative of coconut oil, jojoba oil, and aloe vera. In a recent study involving two cohorts, the infestation rates dropped 92% on average for the first one and 90% for the other. Likewise, the intensity of the cohorts dropped by 86% and 87% respectively. The non-toxic nature of Zanzarin, combined with its "remarkable regression of the clinical pathology" make this a tenable public health tool against tungiasis.

The use of pesticide, like DDT, has also led to elimination of the "Tunga penetrans", but this control/prevention strategy should be utilized very carefully, if at all, because of the possible side effects such pesticides can have on the greater biosphere. In the 1950s, there was a worldwide effort to eradicate malaria. As part of that effort, Mexico launched the Campaña Nacional para la Erradicación de Paludismo, or the National Campaign for the Eradication of Malaria. By spraying DDT in homes, the Anopheles a genus of mosquitoes known to carry the deadly Plasmodium falciparum was mostly eliminated. As a consequence of this national campaign, other arthropods were either eliminated or significantly reduced in number, including the reduviid bug responsible for Chagas disease (American Trypanosomiasis) and "T. penetrans". Controlled, in-home spraying of DDT is effective as it gives the home immunity against arthropods while not contaminating the local water supplies and doing as much ecological damage as was once the case when DDT was first introduced.

While other species gradually gained resistance to DDT and other insecticides that were used, "T. penetrans did" not; as a result, the incidence of tungiasis in Mexico is very low when compared to the rest of Latin America, especially Brazil, where rates in poor areas have been known to be as high or higher than 50%. There was a 40-year period with no tungiasis cases in Mexico. It was not until August 1989 that three Mexican patients presented with the disease. Though there were other cases of tungiasis reported thereafter, all were acquired in Africa.

Tungiasis (also known as "nigua", "pio" and "bicho de pie", or "pique" or sand flea disease) is an inflammatory skin disease caused by infection with the female ectoparasitic "Tunga penetrans" (also known as chigoe flea, jigger, nigua or sand flea), found in the tropical parts of Africa, the Caribbean, Central and South America, and India. "Tunga penetrans" is the smallest known flea, measuring 1 mm across. It is also known in Latin America as the "nigua" and "bicho de pie" (Spanish) or "bicho de pé" (Portuguese), literally ""foot bug"". "Tunga penetrans" is a member of the genus "Tunga", which comprises 13 species.

Tungiasis causes skin inflammation, severe pain, itching, and a lesion at the site of infection that is characterized by a black dot at the center of a swollen red lesion, surrounded by what looks like a white halo. Desquamation of the skin is always seen, especially after the flea expands during hypertrophy.

As of 2009, tungiasis is present worldwide in 88 countries with varying degrees of incidence. This disease is of special public health concern in highly endemic areas such as Nigeria, Trinidad and Tobago, and Brazil, where its prevalence, especially in poor communities, has been known to approach 50%.

The chigoe flea is properly classified as a member of the order Siphonaptera as it is a flea. Although commonly referred to as chiggers, true chiggers are mites which are minute arachnids. Mites penetrate the skin and feed on skin cells that are broken down by an enzyme they secrete from their mouthparts, but they do not lay eggs in the host as "T. penetrans" does. Moreover, in mites, the adult and the larval forms both feed on other animals. This is not the case with "T. penetrans", as only the adults feed on mammals and it is only the female that stays attached to the host.

"Tunga penetrans" is also known by the following names: chigoe flea, sand flea, nigua, chigger flea, jigger flea, bicho de pé, pico, sikka, kuti, and piqui, among many others.

The diagnosis of flea allergy dermatitis is complicated by the grooming habits of pets. Cats in particular are very efficient at grooming out fleas, often removing any evidence of infestation. Fleas begin biting within 5 minutes of finding a host, and there are no flea treatments that kill fleas before biting occurs.

It is caused by either "Bartonella henselae" or "B. quintana".

- "B. henselae" is most often transmitted through a cat scratch or bite, though ticks and fleas may also act as vectors.

- "B. quintana" is usually transmitted by lice.

It can manifest in people with AIDS and rarely appears in those who are immunocompetent.

While curable, BA is potentially fatal if not treated. BA responds dramatically to several antibiotics. Usually, erythromycin will cause the skin lesions to gradually fade away in the next four weeks, resulting in complete recovery. Doxycycline may also be used. However, if the infection does not respond to either of these, the medication is usually changed to tetracycline. If the infection is serious, then a bactericidal medication may be coupled with the antibiotics

If a cat is carrying "Bartonella henselae", then it may not exhibit any symptoms. Cats may be bacteremic for weeks to years, but infection is more common in young cats. Transmission to humans is thought to occur via flea feces inoculated into a cat scratch or bite, and transmission between cats occurs only in the presence of fleas. Therefore, elimination and control of fleas in the cat's environment are key to prevention of infection in both cats and humans.

The flea found most commonly on both dogs and cats with a flea infestation is the cat flea, "Ctenocephalides felis". Pets that develop FAD have an allergic response to flea saliva injected during flea feeding. The itch associated with just one flea bite persists long after that flea is gone and leads to significant self-trauma.

Pulicosis (also known as "flea bites") is a skin condition caused by several species of fleas, including the cat flea ("Ctenocephalides felis") and dog flea ("Ctenocephalides canis"). This condition can range from mild irritation to severe irritation. In some cases, 48 to 72 hours after being bitten, a more severe rash-like irritation may begin to spread across the body. Symptoms include swelling of the bitten area, erythema, ulcers of the mouth and throat, restlessness, and soreness of the areolae. In extreme cases, within 1 week after being bitten, the condition may spread through the lymph nodes and begin affecting the central nervous system. Permanent nerve damage can occur.

If they receive an excessive number of bites, pets can also develop flea allergy dermatitis, which can potentially be fatal if no actions are taken. However, dogs and cats are not the only ones that are at risk. Humans can suffer from flea bites and, depending on a variety of factors, the bites can cause much pain and discomfort.

Placing the cat's water in a shallow dish may prevent the chin from absorbing the bacteria in the water while the cat is drinking. If the cat is allergic to plastics or dyes, using a stainless-steel or glass dish is recommended . Cats may also have food allergies that make the development of acne more likely, so that switching kibble, or changing to a hydrolysed diet may be effective. Maintaining good hygiene and grooming habits make the development of feline acne less likely. Washing and exfoliating the chin with a gentle benzoyl-peroxide solution also may be preventive of further outbreaks.

The most important infectious skin diseases of cats is ringworm or dermatophytosis. Other cat skin infections include parasitic diseases like mange and lice infestation.

Other ectoparasites, including flea and tick infestations are not considered directly contagious but are acquired from an environment where other infested hosts have established the parasite's life cycle.

Another common skin infection is cat bite abscess. A mixture of bacteria introduced by a bite wound cause infections in pockets under the skin and affected cats often show manic depression and fever.

Atopy is a hereditary and chronic (lifelong) allergic skin disease. Signs usually begin between 6 months and 3 years of age, with some breeds of dog, such as the Golden Retriever showing signs at an earlier age. Dogs with atopic dermatitis are itchy, especially around the eyes, muzzle, ears and feet. In severe cases the irritation is generalised. If the allergens are seasonal, the signs of irritation are similarly seasonal. Many dogs with house dust mite allergy have perennial disease. Some of the allergens associated with atopy in dogs include pollens of trees, grasses and weeds, as well as molds and House dust mite. Ear and skin infections with the bacteria "Staphylococcus pseudintermedius" and the yeast "Malassezia pachydermatis" are common secondary to atopic dermatitis.

Food allergy can be associated with identical signs and some authorities consider food allergy to be a type of atopic dermatitis.

Diagnosis of atopic dermatitis is by elimination of other causes of irritation including fleas, scabies and other parasites such as Cheyletiella and lice. Food allergy can be identified through the use of elimination diet trials in which a novel or hydrolysed protein diet is used for a minimum of 6 weeks and allergies to aeroallergens can be identified using intradermal allergy testing and/or blood testing (allergen-specific IgE ELISA).

Treatment includes avoidance of the offending allergens if possible, but for most dogs this is not practical or effective. Other treatments modulate the adverse immune response to allergens and include antihistamines, steroids, ciclosporin and immunotherapy (a process in which allergens are injected to try to induce tolerance). In many cases shampoos, medicated wipes and ear cleaners are needed to try to prevent the return of infections.

New research into T-cell receptor peptides and their effects on dogs with severe, advanced atopic dermatitis are being investigated.

The cat must have a supply of niacin, as cats cannot convert tryptophan into niacin like dogs. However, diets high in corn and low in protein can result in skin lesions and scaly, dry, greasy skin, with hair loss. Another B vitamin, biotin, if deficient causes hair loss around the eyes and face. A lack of B vitamins can be corrected by supplementing with a vitamin B complex, and brewers yeast.

Until recently humans and water fleas ("Cyclops") were regarded as the only animals this parasite infects. It has been shown that baboons, cats, dogs, frogs and catfish ("Synodontis") can also be infected naturally. Ferrets have been infected experimentally.

Pemphigus foliaceus is the most common autoimmune disease of the dog. Blisters in the epidermis rapidly break to form crusts and erosions most often affecting the face and ears initially, but in some cases spreading to include the whole body. The pawpads can be affected causing marked hyperkeratosis (thickening of the pads with scale). Other autoimmune diseases include bullous pemphigoid and epidermolysis bullosa acquisita.

Treatment of autoimmune skin conditions requires treatment to markedly reduce the abnormal immune response; steroids, azathoprine and other drugs are used as immunosuppressive agents.

Cat-scratch disease has a worldwide distribution, however it is a nonreportable disease in humans and therefore public health data on this disease is inadequate. Geographical location, present season and variables associated with cats (such as exposure and degree of flea infestation) all play a factor in the prevalence of Cat-scratch disease within a population. In warmer climates, the incidence of Cat-scratch disease is more prevalent during the fall and winter months. The higher rate of Cat-scratch disease during those months may be attributed to the breeding season for adult cats, which allows for the birth of kittens". B henselae," the bacterium responsible for causing Cat-scratch disease, is more prevalent in younger cats [less than one year old] than it is in adult cats.

To determine recent incidence of Cat-scratch disease in the United States, the Truven Health MarketScan Commercial Claims and Encounters database was analyzed in a case control study from 2005-2013. The database consisted of healthcare insurance claims for employees, their spouses, and their dependents. All participants were under 65 years of age, from all 50 states. The length of the study period was 9 years and was based off 280,522,578 person-years; factors such as year, length of insurance coverage, region, age, and sex were used to calculate the person-years incidence rate to eliminate confounding variables among the entire study population. 13,273 subjects were diagnosed with Cat-scratch disease, both in and outpatient cases were analyzed. The study revealed an incidence rate of 4.5/100,000 outpatient cases of Cat-scratch disease. For inpatient cases, the incidence rate was much lower at 0.19/100,000 population. Incidence of Cat-scratch disease was highest in 2005 among outpatient cases and then slowly declined. The Southern states saw the most significant decrease of incidence overtime. Mountain regions have the lowest incidence of this disease because fleas are not a common vector found in these areas.

Distribution of Cat-scratch disease among children aged 5-9 were of the highest incidence in the analyzed database, followed by woman aged 60-64. Incidence among female patients was higher than that among male patients in all age groups. According to data on social trends, women are more likely to own a cat over men; which supports higher incidence rates of this disease in women. Risk of contracting Cat-scratch disease increases as the number of cats residing in the home increases. The number of pet cats in the United States is estimated to be at 57 million. Due to the large population of cats residing in the United States, the ability of this disease to continue to infect humans is vast. Laboratory diagnosis of Cat-scratch disease has improved in recent years, which may support an increase in incidence of Cat-scratch disease in future populations.

The cat should be taken to a veterinarian. The most suspected cause of skin problems in cats will be fleas. Other causes of over-grooming are not as easily ascertained. As household antiseptics are known to be toxic to cats, veterinary antiseptics for cats can be used to treat open sores, if they do occur. Sores can also be treated with cream, oral or injected anti-inflammatories, however if the problem continues to recur it may be more cost effective to subject the cat to laboratory testing early on. It may be difficult to keep a clean dressing on a cat's belly, and an anti-lick collar is adequate to let the wound heal. If an anti lick collar is used, a soft anti-lick collar is less cumbersome, although they are less durable. If the cat wears a plastic anti-lick collar, it may use the edge of the collar to grind against existing wounds, making them worse. A soft anti lick collar will become less effective as it is kicked out of the shape by the cat's hind leg, and will need prompt replacement. The cat can sanitize the wound if the collar is removed for daily short periods of time, also giving the cat an opportunity for an overall grooming. Scratches and wounds can heal completely using this method. When the cat stops wearing the collar, thinned hair, redness of skin or cracked nipples on the cat are early indicators that the cat has started to over-groom again.

Antidepressants for cats may be suggested by a vet.

Carrión's disease, or Oroya fever, or Peruvian wart is a rare infectious disease found only in Peru, Ecuador, and Colombia. It is endemic in some areas of Peru, is caused by infection with the bacterium "Bartonella bacilliformis", and transmitted by sandflies of genus "Lutzomyia".

Cat scratch disease occurs worldwide. Cats are the main reservoir of "Bartonella henselae", and the bacterium is transmitted to cats by the cat flea "Ctenocephalides felis". Infection in cats is very common with a prevalence estimated between 40-60%, younger cats being more commonly infective. Cats usually become immune to the infection, while dogs may be very symptomatic. Humans may also acquire it through flea or tick bites from infected dogs, cats, coyotes, and foxes.

Trench fever, produced by "Bartonella quintana" infection, is transmitted by the human body louse "Pediculus humanus corporis". Humans are the only known reservoir. Thorough washing of clothing may help to interrupt the transmission of infection.

A possible role for ticks in transmission of "Bartonella" species remains to be elucidated; in November 2011, "Bartonella rochalimae", "B. quintana", and "B. elizabethae" DNA was first reported in "Rhipicephalus sanguineus" and "Dermacentor nitens" ticks in Peru.

Dracunculiasis is caused by drinking water contaminated by water fleas that host the "D. medinensis" larvae. Dracunculiasis has a history of being very common in some of the world's poorest areas, particularly those with limited or no access to clean water. In these areas, stagnant water sources may still host copepods, which can carry the larvae of the guinea worm.

After ingestion, the copepods die and are digested, thus releasing the stage 3 larvae, which then penetrate the host's stomach or intestinal wall, and then enter into the abdominal cavity and retroperitoneal space. After maturation, which takes approximately three months, mating takes place; the male worm dies after mating and is absorbed by the host's body.

Approximately one year after mating, the fertilized females migrate in the subcutaneous tissues adjacent to long bones or joints of the extremities. They then move towards the surface, resulting in blisters on the skin, generally on the distal lower extremity (foot). Within 72 hours, the blister ruptures, exposing one end of the emergent worm. The blister causes a very painful burning sensation as the worm emerges, and the sufferer will often immerse the affected limb in water to relieve the burning sensation. When a blister or open sore is submerged in water, the adult female releases hundreds of thousands of stage 1 guinea worm larvae, thereby contaminating the water.

During the next few days, the female worm can release more larvae whenever it comes in contact with water, as it extends its posterior end through the hole in the host's skin. These larvae are eaten by copepods, and after two weeks (and two molts), the stage 3 larvae become infectious and, if not filtered from drinking water, will cause the cycle to repeat. Infected copepods can live in the water for up to four months.

The male guinea worm is typically much smaller () than the female, which, as an adult, can grow to long and be as thick as a spaghetti noodle.

Infection does not create immunity, so people can repeatedly experience Dracunculiasis throughout their lives. Several worms may emerge simultaneously; the average is 1.8. Up to 14 worms have been reported in one individual.

In drier areas just south of the Sahara desert, cases of the disease often emerge during the rainy season, which for many agricultural communities is also the planting or harvesting season. Elsewhere, the emerging worms are more prevalent during the dry season, when ponds and lakes are smaller and copepods are thus more concentrated in them. Guinea worm disease outbreaks can cause serious disruption to local food supplies and school attendance.

The infection can be acquired by eating a fish paratenic host, but this is rare. No reservoir hosts are known; that is, each generation of worms must pass through a human – or possibly a dog.

Areas affected are those the cat can access most easily, including the abdomen, legs, flank, and chest.

- Baldness, usually beginning with the abdomen

- Obvious over-grooming (although some cats may only engage in the behavior in the absence of owners)

- Redness, rashes, pus, scabs on the bald area or areas traumatized by over-grooming

- A highly irritable cat may even cut its face with the claw of its hind foot if over-zealously scratching the back of its head.

Cat-scratch disease can be primarily prevented by taking flea control measures and washing hands after handling a cat or cat feces; since cats are mostly exposed to fleas when they are outside, keeping cats inside can prevent infestation.

Treatment of infections caused by "Bartonella" species include:

Some authorities recommend the use of azithromycin.

Sylvatic plague is most commonly found in prairie dog colonies; the flea that feeds on prairie dogs (and other mammals) serves as the vector for transmission to the new host.

Sylvatic plague is an infectious bacterial disease caused by the bacterium "Yersinia pestis" that primarily affects rodents such as prairie dogs. It is the same bacterium that causes bubonic and pneumonic plague in humans. Sylvatic, or sylvan, means 'occurring in wildlife,' and refers specifically to the form of plague in rural wildlife. Urban plague refers to the form in urban wildlife.

It is primarily transmitted among wildlife through flea bites and contact with infected tissue or fluids. Sylvatic plague is most commonly found in prairie dog colonies and some mustelids like the black-footed ferret.