Diseases transmitted by animals  (also known as zoonoses) these are such infectious and parasitic diseases which may communicate to humans from ill animals or animals which are not necessarily sick themselves but are hosts for viruses, bacteria, fungi or parasites.

Parasites  not only live in or on birds but also may carry many diseases. Pigeons are infested by such parasites as ticks, mites feeding on their carriers blood, scabies mites feeding on epidermis, parasitizing in feathers and dermal papillae. Also hemipterans and fleas feeding on blood are dangerous, especially for nestlings which may get anaemia due to blood loss.
Ticks and bugs may attack humans and other animals, they may also transmit cholera. From among skin parasites, scabies mites cause inflammatory condition of skin.

THESE ARE ONLY SOME OF MANY DANGEROUS DISEASES WHICH MAY BE TRANSMITTED BY BIRDS:

Aspergillosis is a fungal infection attacking respiratory and gastrointestinal tracts in birds. Aspergillus is a group of mould fungi which are found world-wide. They are very common in autumn and winter in the Northern hemisphere. Some of them may cause infections in humans and animals. They come in various forms, starting from typical allergic diseases and ending with general life-threatening infections. Course of a disease depends on various factors but one of the most important of them is individual condition of the immune system. When developing, the fungus forms grey-and-green mildewy coating on wet, decaying wood or wet bedding material in nests, from where it easily gets to gastrointestinal and respiratory tracts of a bird, causing inflammatory conditions. This disease is curable only in its initial stage but usually is recognized only when it is too late for effective treatment. There are several types of Aspergillosis:

Allergic Bronchopulmonary Aspergillosis (ABPA)  this is a condition which produces an allergy to the spores of the aspergillus moulds. It is quite common in asthmatics; up to 20% of asthmatics might get this at some time during their lives. ABPA is also common in cystic fibrosis patients, as they reach adolescence and adulthood. The symptoms are similar to those of asthma: intermittent episodes of feeling unwell, coughing and wheezing. Some patients cough up brown-coloured plugs of mucus. The diagnosis can be made by X-ray or by sputum, skin and blood tests. In the long term, ABPA can lead to permanent lung damage (fibrosis) if untreated.  

Aspergilloma (also known as Fungus Ball, Mycetoma) this is a very different disease from ABPA also caused by the Aspergillus mould. The fungus grows within a cavity of the lung, which was previously damaged during an illness such as tuberculosis or sarcoidosis. Any lung disease which causes cavities can leave a person open to developing an aspergilloma. The spores penetrate the cavity and germinate, forming a fungal ball within the cavity. The fungus secretes toxic and allergic products which may make the person feel ill. The person affected may have such symptoms (especially early on) as weight loss, chronic cough. While feeling rundown are common symptoms later. Coughing of blood (haemoptysis) can occur in up to 50-80 % of affected people. 

Invasive aspergillosis  many people with a damaged or impaired immune system die from invasive aspergillosis. Their chances of living are improved the earlier the diagnosis is made but unfortunately there is no good diagnostic test. Often treatment has to be started when the condition is only suspected. The symptoms of invasive aspergillosis are: fever, cough, chest pain, discomfort or breathlessness. Sometimes the fungus can transfer from the lung through the blood stream to other organs, including the brain, the eye, the heart, the kidneys and the skin. These are very dangerous cases which cause higher risk of death.

Ornithosis (also known as Avian Chlamydiosis or Psittacosis) this is a very dangerous viral disease, easily affecting the whole flocks. Infection is caused by direct contact with infected birds, contaminated water, faeces of infected pigeons, as well as by inhalation of dust contaminated with affected faeces. This disease may be carried also by Acarina and Mallophaga (biting lice) feeding on birds blood. It must be remembered that ornithosis is very dangerous also to humans. It might be useful to mention that ornithosis is an officially eradicated disease.

Salmonellosis (also known as Typhoid Fever, Salmonella Infection) this is a disease caused by bacteria called Salmonella living in contaminated faeces of infected birds. Young birds are the most prone to infection, older birds show considerable immunity to it. The symptoms which usually develop already after a few days of infection are: increased thirst accompanied by loss of appetite, ruffling up of feathers and sagging wings, convulsions, paraparesis and acute diarrhoea. Young birds die after a few days.

Sarcoptes Scabiei (also known as Itch Mites) attack pigeons in various ways: young specimens occur in hypodermis, intoxicating them at the same time with products of their metabolism; adult itch mites live between feathers causing itching and fragility of birds feathers.

Mallophaga (also known as Biting Lice, Pigeon Body Lice) are found among pigeons in two forms: one, called the slender pigeon louse, occurs on flight feathers, the neck, the chest, and sometimes on the head, damaging mainly wing feathers, which may even prevent the bird from flying; the other type is Hohorstiella gigantea lata occurring on chest skin and the fore part of the body and besides damaging feathers it also feeds on pigeons blood, which additionally may transfer an infectious disease. 

Helminthiasis this is a disease in which the gastrointestinal tract of the bird is infested with such parasites as pinworms, roundworms and tapeworms. This disease causes exhaustion of the bird, intoxicated additionally by toxic excrements of parasites, which leads to its death, and furthermore to infection of other birds with parasites excreted in large quantities by the affected bird with faeces. The disease is always caused by feed or drinking water contaminated by faeces of the affected animal. Already after nearly 19 days after the bird swallows a worms egg, e. g.  trichinosis, adult parasites are present in the gastrointestinal tract and after another 7 days produce eggs which are excreted with faeces. Helminthiasis of the pigeons gastrointestinal tract pose serious threat to health of other animals and humans. At risk are especially young children whose immune system is not fully developed and fails to resist the invasion, the more so that children are not able to sufficiently care for hygiene. It is estimated that each year thousands of children are infected by endoparasites and several percent has serious problems with sight (including loss of vision) as a consequence of migration of larva stages.   

Coccidiosis, also known as bloody diarrhoea, is caused by a protozoon of the Coccidium pfeiferi group. Infection occurs either through direct contact or indirectly by staying in the place contaminated with faeces of affected pigeons. This disease reveals itself within 3-7 days after infection. Symptoms are: lack of appetite and lack thirst, apathy, diarrhoea, emaciation, convulsions. It usually results in death of the bird or other infected animal. 

Trichomoniasis, also known as canker, caused by the protozoan Trichomonas gallinae. This is principally a disease of young birds which are infected by their parents. Older pigeons also may be infected by Trichomonas gallinae through water. The disease has often the form of large crusts on the skin, it attack also mucous membrane of the front part of the gastrointestinal track and other internal organs of the bird, such as the liver, pancreas or lungs, causing abscesses. The infected bird has a thicker neck, sagging wings and diarrhoea. The disease is very exhausting, usually lasts only 1-4 days and results in death of the bird from cachexia.  

Ticks (fowl tick) feeding on blood, when occurring in large number pose serious danger to life of birds, especially young ones, which sometimes can be so exhausted and weak due to loss of blood that they have no strength to fly and often even die. Ticks are also carriers of the disease dangerous also for humans - borreliosis.  

Borreliosis is a multiorgan and multistage disease. It is caused by treponemas (Borrelia burgdorferi) transmitted by all forms of ticks, therefore it is also called treponematosis. Bacteria are spread by small rodents, deer as well as birds, including pigeons and swallows. This disease is very often. It affects everyone who had contact with Borrelia burgdorferi. Fortunately not all the ticks are infected, although in some areas there are 15-20% of them. Sometimes the final stage are like flue symptoms. But it also happens that after a period of a relative health the disease recurs and may be fatal.

This disease, known also as treponematosis or Lyme disease, is a chronic bacterial infection, during which the skin and/or many internal organs and systems are affected. The etiological factor is a treponema from the Spirochetaceae family. There are 4 subtypes of treponemas: Borrelia burgdorferi, Borrelia garini, Borrelia afzeli and Borrelia japonica. Infection occurs as a result of the bite by a hard-bodied (Ixodes species) tick that is infected with pathogenic Borrelia burgdorferi. B. burgdorferi penetrate to the ticks gastrointestinal tract and become active after intestines are filled with blood when feeding on the hosts skin. At that time they start to multiply, get to body fluids and organs, including salivary glands. Humans become infected when the infected tick bites into their skin and during blood sucking by discharge of ticks saliva or vomit. Usually the very moment of cutting the epidermis and blood sucking is unnoticeable as ticks secretion has anaesthetic effect. Only after 2-3 days characteristic itching occurs and the tick filled up with blood becomes bigger and therefore more visible. Probability that infection will be transmitted depends on the period of time during which the tick sits in the skin; on the third day it reaches 100%. Most often borreliosis is a symptom complex involving skin and as the infection spreads, joints, the nervous system and the cardiovascular system. B. burgdorferi after penetrating through the skin spread within in it in several days and get into the blood stream, but they may also spread through lymphatic vessels and along peripheral nerves. Borreliosis has been divided into three stages, based on the time of onset following the tick bite: 

Stage I  early infection, developing from 60 to 90 days after the thick bite, in the form of limited skin changes such as erythema chronicum migrans (ECM) and sometimes lymphocytoma (LBC).

Stage II  infection generalization, during which skin changes (LBC) develop further and acute inflammatory changes occur in organs involving joints, the heart, the peripheral and central nervous system.

Stage III  chronic infection, starting after more than 1 year to several years after infection. In this period skin changes occur in the form of acrodermatitis chronica atrophicans (ACA) and destructive  inflammatory changes in joints, chronic encephalitis and cerebrospinal meningitis.

Bird Flue (Avian Influenza) this disease has been known since 1901. For the first time it was discovered and described in Italy. In 1955 the pathogen causing it was identified. This is an infectious disease which attacks wildfowl and domestic poultry, caused by the type A of influenza virus. Particles of influenza virus may infect also other species of animals, including pigs, horses, seals, whales, and humans. However, this is wildfowl that acts as the natural and asymptomatic carrier, spreading influenza virus among more susceptible to infection domestic poultry.
Infection with avian influenza virus can sporadically occur in humans. However, the course of the disease is much more severe than in case of regular human influenza. In few cases the following symptoms were observed: fever, sore throat, cough. It may be followed by viral pneumonia leading to acute respiratory failure.

The main source of the threat to humans and animals (poultry) is birds living in the wild (mainly water birds), being asymptomatic carriers of avian influenza. The most probable source of infection for domestic poultry is direct or indirect contact (drinking water) with such birds. Avian influenza virus may spread in air as well as through manure. Besides water the source of potential infection may be contaminated feed and not disinfected working clothes and equipment as well as contaminated means of transportation.    

The main portal of infection is through contact with faeces of infected birds. Avian influenza virus may also be carried on shoes as well as by rodents, extending in this way the scale of threat. Therefore, people working on poultry farms or even those keeping only a few hens are mostly exposed to infection with avian influenza. Infection may also be transmitted to humans by way of contact with faeces of wildfowl, however no cases of infections transmitted in this way have been reported so far and all cases of the disease in humans have originated from domestic poultry.