Gamasoidosis

Gamasoidosis, also known as dermanyssosis, is a frequently unrecognized form of dermatitis, following human infestation with avian mites of the genera Dermanyssus or Ornithonyssus. It is characterized by pruritic erythematous papules, macules and urticaria, with itching and irritation resulting from the saliva the mites secrete while feeding. These bites are commonly found around the neck and areas covered by clothing, but can be found elsewhere on the body. The avian mite Dermanyssus gallinae can also infest various body parts, including the ear canal and scalp.

Diagnosis is challenging due to the small size of the mites, requiring microscopic examination by a medical entomologist for species identification. Misdiagnosis is also common due to ignorance and misinformation among medical professionals, scientists and pest controllers. Gamasoidosis is linked to avian mites infesting residential, public and agricultural spaces, with a potential health threat due to the transmission of zoonotic pathogens by D. gallinae. Treatment involves eradicating mites from the environment, with resistance to pesticides posing a challenge. The condition's epidemiology raises concerns about its impact on public health, emphasizing the need for awareness, interdisciplinary collaboration, improved diagnostic tools and a "One Health" approach.

Signs and symptoms
Avian mite bites induce a non-specific dermatitis. The most common symptoms are pruritic erythematous papules, with a size of 1–3 mm, and a central punctum, as well as macules and urticaria. Itching and skin irritation are reactions to the saliva the mites secrete when feeding.

Bites are normally located in groups around the neck and body areas covered by clothes (waist, trunk, upper extremities and abdomen), but can also be found on the legs, finger webs, axillae, the groin, and buttocks. If feeding occurs while a patient is sleeping, bedding may show red spots caused by droppings or crushed mites.

The species Dermanyssus gallinae is capable of infesting the ear canal, with symptoms including itching, internal inflammation and discharge. It can also infest the scalp, with severe itching, particularly at night, as the primary symptom, as well as "the nares, orbits and eyelids, and genitourinary and rectal orifices."

Additional symptoms include pinpricks, secondary infections, scarring and hyperpigmentation.

Causes
Gamasoidosis occurs after human contact with avian mites which infest birds, such as canaries, sparrows, starlings, pigeons and poultry and is caused by two genera of mites: Ornithonyssus and Dermanyssus. Avian mite species implicated include the red mite (Dermanyssus gallinae), tropical fowl mite (Ornithonyssus bursa) and northern fowl mite (Ornithonyssus sylviarum)''.  Dermatitis is also associated with rodents infested with the tropical rat mite (Ornithonyssus bacoti), spiny rat mite (Laelaps echidnina) and house-mouse mite (Liponyssoides sanguineus''), where the condition is known as rodent mite dermatitis. Urban gamasoidosis is associated with window-sills, ventilation and air-conditioning intakes, roofs and eaves, which serve as shelters for nesting birds. Gamasoidosis in farm workers is associated with poultry farms, with a "19% incidence of contact dermatitis reported in a two-year survey of workers on 58 European poultry farms"; D. gallinae exposure is so common that it is considered an "occupational hazard" for these workers.

Diagnosis
Diagnosis can be challenging as the small size of avian mites make them "barely visible to the unaided eye". Identification of the species is best carried out by a medical entomologist using a microscope; positive identification of species is critical for recommendation of suitable treatment methods.

Diagnoses of gamasoidosis have a long history, with "cases [...] reported since the 17th century, documented in the leading medical literature since at least the 1920s." Avian and rodent mites have been documented as infesting residential buildings, work spaces, schools and hospitals. Despite this, there is considered to be widespread ignorance and misinformation "regarding human infestation with D. gallinae across healthcare, science and pest control fields", which in turn has led to increasing numbers of infestations and a dangerous propagation of the disease.

Due to it being an uncommon diagnosis, physicians are generally not aware of the condition, meaning gamasoidosis may be unrecognized or misdiagnosed as conditions such as contact dermatitis caused by allergies, scabies caused by Sarcoptes scabiei, infestation by body lice (Pediculus humanus corporis) leading to pediculosis, tropical rat mite bites (O. bacoti), infestation by pigeon ticks (Argas reflexus), chigger mite bites (Trombiculidae), bites from Cheyletiella mitesm, or bed bugs (Cimex lectularius).

Many cases of gamasoidosis go unreported, suggesting that the actual incidence is higher than generally believed. As a result, in cases of unexplained bites in residential areas, the involvement of D. gallinae should always be considered, especially during late spring and early summer when wild birds make their nests.

The life cycle of the mite is another important method of diagnosis. Hematophagic mites generally feed at night, but may also feed during the day if the room is sufficiently dark. Attacks in public and office buildings tend to occur during the daytime. O. bursa is an exception as it generally remains on its hosts and will feed during the day. D. gallinae may be commonly found in the bedroom or where the patient sleeps, as they prefer to stay close to their host for optimal feeding. D. gallinae generally visit their host for up to 1–2 hours, leave after completing their blood meal, and typically feed every 2–4 days. They are able to move extremely quickly, and can take less than 1 second to bite; enough time to inject their saliva and to induce rash and itching. They locate potential hosts through temperature changes, vibrations, chemical signals and.

It has been hypothesized the D. gallinae is capable of 'learning' "to associate non-host skin with a blood-meal if the host selection process permitted feeding." Combined with a generalist approach to finding hosts and the capability of digesting non-avian blood could potentially explain their documented host expansion to mammals and humans.

There is documented "co-occurrence of gamasoidosis and various immunosuppressive disorders" and physicians should bear in mind that immunocompromised patients, patients that take corticosteroids, and patients with dementia may have a more severe infestation than healthy patients, Despite this, while immunosuppression can "increase susceptibility, it is not necessarily a pre-requisite for infestation".

Dermatoscopy can help to exclude the diagnosis of delusional parasitosis.

Pets such as canaries, cats, dogs, hamsters, and gerbils can be infested also. As a result, it has been argued that veterinarians should be aware that non-avian attacks of D. gallinae are possible, and may be underestimated, and that there is a need for increased awareness among practitioners.

Prevention
Preventing gamasoidosis in residential areas is achieved by avoiding the proliferation of avian mites, by refraining from feeding birds and utilizing nets on building terraces to deter nesting in close proximity to human homes. It is crucial to remove and clean nests during the nesting season before birds can establish them and lay eggs.

Treatment
Treatment of gamasoidosis can be difficult; avian mites have developed resistance to multiple pesticides and the different species concerned display varied ecologies that necessitate divergent treatment approaches.

For a patient to achieve full recovery, the mites must be eradicated from the person's environment through the removal of nests and appropriate disinfestation of infested areas by a pest control professional. Total eradication can be difficult to achieve as D. gallinae can survive for longer than nine months without a blood meal, and is capable of both digesting, and completing its life cycle on human blood alone. Additionally, populations can expand rapidly, with a single female capable of laying up to "30 eggs in their lifetime"; prolonged darkness has been found to significantly promote mite population growth.

Patients are advised to:
 * Shower frequently.
 * Wash clothes at 60 °C.
 * Remove the source of the mites, such as bird nests.
 * Perform regular intensive vacuum cleaning and steam cleaning — the vacuum bag should be placed in a sealed bag and thrown away outside in a contained bin.
 * Disinfect infested areas with pyrethroids.
 * Wash of textiles or steam cleaning (cushions, carpets, curtains) at 60 °C, and drying them using an automated laundry drier.

Antihistamines and topical corticosteroids can be used for temporary relief of symptoms.

In the case of scalp infestation, treatments with 1% permethrin shampoo can be used to remove the mites. For ear canal infestation, aural toilet is recommended with a course of 1% permethrin to be used as ear drops and for infected wax to be removed by a professional.

Ineffective and often prolonged attempts to eradicate infestations can result in economic issues, due to a significant financial outlay when patients relocate or attempt to control these infestations, as well as psychological problems such as depression.

For pets, there are currently no registered products for treating gamasoidosis in mammals. The scientific literature documents medications which have been used off-label to treat the condition, including sarolaner in dogs, selamectin in cats and permethrin in horses.

Epidemiology
Gamasoidosis, particularly caused by D. gallinae, is source of growing concern in human medicine, due to factors such as limited awareness among medical specialists, lack of interdisciplinary collaboration, misdiagnoses, and an absence of diagnostic tools. Occurrences of gamasoidosis have become more frequent in recent years, especially in residential environments, often linked to synanthropic birds. A "One Health" approach has been recommended to remedy this, with microbiologists, veterinarians, parasitologists, epidemiologists, environmental scientists, and clinicians working together to treat the disease.

D. gallinae may pose a threat to public health as the mite may be a vector or reservoir of several zoonotic pathogens, such as Chlamydia psittaci, Erysipelothrix rhusiopathiae, Salmonella spp., Mycobacterium spp., Coxiella burnetii, Bartonella spp., Borrelia afzelii, Venezuelan equine encephalitis virus, Eastern equine encephalitis virus, and Fowlpox virus. An association has not been found with gamasoidosis and alpha-gal allergy.