The diseases of animals transmissible to man are known as "zoonoses". Those affecting birds include psittacosis (also known as ornithosis and chlamydiosis), salmonellosis, pseudotuberculosis, tuberculosis, erysipelas, pasteurellosis and Newcastle's disease. All seven diseases are capable of infecting man, but only the first four are of any importance, the remainder being merely of academic interest. These diseases are not common in man nor indeed in parrots, with the exception of psittacosis and salmonellosis, both of which occur most frequently in recently imported birds. In this paper, we shall examine the more important diseases, concentrating on the way they are transmitted to birds and man; the clinical signs shown by birds and the symptoms in man.
In spite of the fact that this disease has attracted a lot of publicity in recent years, some parrot keepers still do not seem to take it seriously. An account of how I and one of my technicians contracted the disease whilst working at London Zoo, following post mortem examinations on infected Amazon parrots, may serve to emphasize its importance. In both instances we took reasonable precautions, including the wearing of face masks, rubber gloves and other protective clothing which on previous occasions had appeared to be adequate. Ten days after the post mortem examinations, we developed severe flu-like symptoms. These included a fever of 105 degrees F, violent shivering or rigors and severe headaches. The infection did not spread to other people in my household, as it probably would have done had it been influenza. Psittacosis was not strongly suspected by the doctor at the time and I responded only slowly to treatment with ampicillin. The disease was confirmed more quickly in the technician and he responded well to the more satisfactory treatment using tetracyclines.
Probably the most common method of infection by psittacosis is by inhalation of dust and particles of excreta containing the causal organism Chlamydia psittaci. It is essential, therefore, when cleaning out accommodation to dampen the bottom of cages and aviaries. It is a sensible precaution to wear a face mask and even eye-shields, especially if recently-imported birds are involved. The disease can also be transmitted by bites from infected birds.
The clinical signs in birds are non-specific and include ruffled feathers, greenish diarrhoea and laboured breathing. There may also be nasal and ocular discharge. Birds may become sick and die within a few days or they may be chronically sick over a period of weeks and lose weight before death. Indeed some birds may show only slight signs of illness and become healthy carriers of the disease over long periods of months or possibly even years.
This is a common bacterial infection of psittacines, especially with recently captured and imported birds which have been under stress. The disease is caused by a large number of different species of Salmonella organisms, although many species are relatively harmless to birds and man under ordinary circumstances. Routine examination of birds dying in quarantine has revealed a higher level of Salmonella infections than had previously been suspected. Salmonella typhimurium is the most common and potentially the most dangerous species. Various types of this organism occur in a wide variety of vertebrates including other birds, mammals (including man) and reptiles. It usually causes an enteric infection, attacking the lining of the gut and producing enteritis. The stomach may also be affected, resulting in gastritis. Sometimes the organism invades the blood stream causing a septicaemia and fever. As with psittacosis, birds can remain healthy carriers of Salmonella organisms and infect others. Human beings can also act as healthy carriers of Salmonella, which is in contrast to man's role in psittacosis.
Salmonella infection in psittacines is not a notifiable disease, but the Divisional veterinary Officer of the Ministry of Agriculture, Fisheries and Food would be glad to hear of any confirmed cases, in order to supplement the data relating to infection in other domestic animals and birds that is recorded under the Zoonoses Order of 1975.
The organism is excreted by infected birds and contamination of their environment, including food receptacles and utensils, readily occurs. The bird keeper must therefore thoroughly wash and disinfect everything that comes in contact with contaminated excreta. He should also wash his hands after dealing with the birds and avoid soiling his clothes. Disposable plastic or rubber gloves should be used if the infection is known to be present and smokers should refrain from putting down cigarettes where they can become contaminated, although ideally, of course, bird keepers should not smoke in the presence of their birds. Although salmonellosis is a potentially important zoonoses there are few records of man becoming infected from psittacine birds.
Diarrhoea, ruffled feathers and lassitude are the main clinical signs in birds. The infection may be acute, killing a bird within a few days, or it may be chronic, resulting in a slow decline in general health with diarrhoea eventually terminating in death. Sometimes, however, illness may not be apparent or may occur only in a mild form.
Symptoms in the main are of a gastrointestinal type, with diarrhoea, vomiting and fever.
This disease is caused by bacteria known as Yersinia (= Pasteurella) pseudotuberculosis. It is particularly common in canaries and toucans and also in monkeys, lagonmorphs (especially hares) and rodents. It is relatively uncommon in psittacine birds and seems to be rare in budgerigars. The disease also occasionally infects man and has been recorded more frequently on the mainland of Europe than in Great Britain.
Routes of infection are the same as for salmonellosis but, in addition, the organism can also enter the body through scratches and abrasions of the skin. Mice, rats or wild birds usually act as the course of the disease by contaminating foodstuffs with their excreta.
The clinical signs in birds are vague and it is only possible to diagnose the disease by post-mortem and bacteriological examination. In birds, the disease is invariably in the form of a septicaemia and produces whitish, necrotic lesions, mainly confined to the liver and spleen. The lesions closely resemble those of tuberculosis hence the name of the disease. The infection is usually chronic, causing sporadic losses over a relatively long period.
The human infection can easily be mistaken for appendicitis, because the bacteria often invade the abdominal lymph nodes in the vicinity of the appendix. Children are mainly affected in this way. Less frequently, the organisms invade the skin or respiratory tract and on rare occasions may produce a septicaemia as occurs in birds.
There are three main strains of this disease - human, bovine and avian. Except from the larger psittacines, only the avian strain is known from birds, this type being common and widespread. Certain parrots (e.g. Amazons and Loris) have the rare distinction of being naturally susceptible to Mycobacterium tuberculosis (the human type) and apparently also capable of being infected with the bovine type, M.bovis.
In the earlier years of this century tuberculosis was much more common in the human population of this country than it is now. The few cases of infection with the human type in psittacines occurred in zoological gardens, where it is likely that the birds contracted the disease from visitors. Public awareness of zoonotic diseases and of the errors of feeding zoo animals was much less than nowadays. Visitors often went to the zoo laden with food for the animals and it was easy for this food to become contaminated by human sputum and other means. Mouth to beak transmission could easily occur when birds nibbled food held in a visitor's mouth. Surprisingly there is no published evidence of birds infecting man although, theoretically, this can occur especially when infected birds with skin lesions (see below) are handled. Tuberculosis of the avian type in birds produces a non-specific malaise, characterised by dull, bedraggled plumage, gradual loss of wight and sometimes diarrhoea. Such birds are referred to as "going light" by bird keepers. Parrots infected with the human type of tuberculosis develop dry, flaky or cheesy encrustations of the skin of the face and around the beak. The lesions are browner in colour than those seen in budgerigars and small psittacines with scaly-face disease (Knemidocoptes pilae mite infestation) and are not pitted.
Avian tuberculosis in man is a relatively rare but serious type of the disease and can take various forms including loss of weight. It is sometimes fatal.
These include bacterial diseases such as erysipelas and pasteurellosis and the viral infection Newcastle Disease (a form of "Fowl Pest"). Although these occur in parrots and can infect man, there is little evidence of parrots actively transmitting these infections.
It is essential that whenever a potential zoonotic infection is suspected in psittacines or other birds, a veterinary surgeon should be consulted and, if it is confirmed, the bird keeper should give his vet the name of his doctor.
Conversely, if a bird keeper ever suspects that he has contracted a disease from his birds, he should give his doctor the name of his vet. In this way appropriate preventive action or treatment can be undertaken as rapidly as possible.
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