Infectious Diseases Of Birds

There are numerous infectious diseases seen in birds; the following is a summarization of the most common agents of disease seen in pet birds. In most cases, prevention is far preferable over treatment of the disease after it occurs. Good nutrition and husbandry are the most important factors in prevention of disease. Keeping the cage clean and free of excessive fecal material and food is important in controlling bacterial infections; decaying food and feces are an ideal growth medium for bacteria which can then overwhelm the normal protective mechanisms that birds have.

A cage should be arranged such that the bird cannot get to the feces to consume them, (a grate on the bottom works in most cases), and the material on the bottom should be easily cleaned on a daily basis, (newspaper, butcher paper, or paper towels are probably the best). Fresh food should be offered to the bird at least once a day, yet should not be left in the cage for longer than 2-3 hours to prevent spoilage. Remember, in the wild, birds live in the trees, so their feces and food drop to the ground below them and they rarely have close contact as they do in cages.

Adequate ventilation is also important in preventing infectious diseases which are more of a problem in confined, small spaces. Housing numerous birds in a single room can allow for the rapid transmission of numerous diseases; many of the bacterial, viral, fungal and chlamydial infections seen in birds are airborne.

One of the most important rules for preventing contagious diseases is the proper isolation of any newly purchased bird prior to introducing it to the rest of the population; this isolation should be for 2 months, (a minimum of a month), and should be in a separate housing area. Most situations do not allow for completely separate housing, yet a different room in the same house should be considered a minimum of isolation. The new bird should be the last to be fed, watered, and handled, and clothes should be changed and hands thoroughly washed with a disinfectant prior to any contact with the original bird population. It needs to be remembered that the incubation period for many of the avian diseases may last for several months, and that the isolation period is one of the best methods to protect the aviary from disease.

At the time of purchase, or within the isolation period, it is also recommended that the newly purchased bird be examined by an avian veterinarian, and that various tests are run to screen for diseases. A thorough physical exam may pick up various problems related to infectious diseases, poor nutrition or husbandry, and should be performed at a minimum. However, in many new bird purchases additional testing should also be planned for to protect the original investment in buying the bird. Blood panels are very informative regarding the health of a bird; they can give an indication of the nutritional status, check for any abnormalities in kidney or liver function, and can detect infections that may not be picked up on the physical exam. Bacterial cultures are also routinely recommended to detect and diagnose the bacterial infections that birds all too frequently carry; most of the time the culture also determines the proper antibiotic that needs to be used to treat the infection. There are specific tests available for the more common viral diseases that are of concern. Psittacine Beak and Feather Disease and Polyoma are the two most current tests available; both tests are very accurate and based on recombinant DNA technology. Testing for Psittacosis is also routinely recommended since this disease can be transmitted to humans; however, the available tests are less accurate and more controversial due to the disease being reportable to the county health department.

VIRAL DISEASES

Psittacine Beak and Feather Disease (PBFD), is a highly contagious viral infection that was originally described in Cockatoos, yet is currently recognized as being potentially contagious to all psittacine birds. Besides the Cockatoos, it is also very common in African Greys and Lovebirds. Newborn chicks with their immature immune systems are at the greatest risk for developing this disease if they are exposed to it. Aviculturists must take steps to protect their aviary and nursery from this airborne virus; strict isolation techniques and screening of birds should be employed to keep an aviary free from PBFD.

Besides exposure in the nursery, the next greatest exposure risk is in situations where a number of birds from different sources are brought together in conditions of stress, such as in a pet shop or a bird fair. Newly purchased birds should be tested for PBFD; this is especially important if introducing them into a household with other birds. Fortunately, there is an accurate test available. The PBFD test currently being used checks for the presence of the virus DNA in the blood of the bird and can also be used to test for the presence of virus particles in the environment. The test is relatively inexpensive and should be included as part of the purchase exam of any high risk species or bird purchased from sources where there is a risk of exposure to the disease. If a bird does test positive, and it is not currently showing clinical signs of the disease, then the test should be repeated in a month. If ,at that time, the test is negative then the bird has managed to eliminate the infection, while if it still tests positive the bird is a viral carrier, and will in all likelihood eventually develop the disease. Such positive birds should be isolated from other birds to minimize the spread of the virus.

The classical form of PBFD in Cockatoos results in abnormal feather development and beak growth. The blood feathers are frequently blunted or may have constrictions in the shaft; these feathers will be abnormal once they reach maturity and will have areas of hemorrhage in the shaft. As the disease progresses, the abnormal feather development makes these birds become featherless to varying degrees. The beaks of affected birds are prone to separation of the different layers, abnormal growth and shape of the beak, and a predisposition to infections of the associated tissues. The problems associated with the beak will cause pain and severely affected birds may be unable to eat due to the discomfort.

Besides attacking the growing beak and feathers, the virus also causes immunosuppresion, which in turn makes the bird very susceptible to other viral, fungal and bacterial infections. In most cases the virus eventually results in the death of the bird. Some species such as Lovebirds seem more resistant to the disease and they may have a chronic infection, yet live a relatively normal lifespan. The virus is shed from infected birds in very high numbers and is present in the feather dust and other excretions; this leads to extensive environmental contamination and to the highly contagious nature of the disease. At this time, there is no treatment or vaccine available to protect against this infection.

Pacheco's Disease is another highly contagious and highly fatal disease seen in most psittacine species. Pacheco's disease is caused by a herpes virus which attacks the liver and results in acute liver failure and death; the typical history on these patients is that they were normal the day before and then either found very weak or dead when they were next checked. The disease is normally diagnosed via necropsy and the distinctive microscopic evidence found in the liver. Treatment of an affected bird is normally just limited to extensive supportive care, yet any other exposed birds should be started on medication in an attempt to minimize the spread of the virus. In Pacheco outbreaks, early treatment with acyclovir, an antiviral medication, is thought to be helpful in cutting down the death rate. Currently there is not an accurate, readily available test to check birds for the presence of this virus. Conures have been implicated as being carriers of this disease, yet any psittacine can probably act as an asymptomatic carrier. Introduction of such a carrier bird into a susceptible population may result in a outbreak of Pacheco's disease. There was a vaccine available that was thought to offer some protective immunity, yet that product is no longer available. (There was a problem with side effects and a few deaths associated with the vaccine.)

Polyoma Virus is of particular importance to aviculturists with an active breeding program. This virus is not particularly deadly in adult birds, yet can cause significant losses in lack of fertility, early embryonic death in the egg, and high chick mortality rates. The virus is thought to be fairly widespread and common, and the current recommendation is that all newly purchased birds should be tested, and that breeding pairs should be tested periodically. The polyoma test is accurate and based on recombinant DNA techniques; however, the bird must be shedding the virus for it to be detected with the test currently available. The test can also be used to confirm the presence of the virus in tissues submitted from a suspicious death. The disease in adult birds often results in liver disease which may progress rapidly to death, although in many cases the infection may only cause moderate illness or even be subclinical. A vaccine has been developed which should offer tremendous benefits to those populations at risk, such as aviaries, pet store birds, or for those people who tend to purchase multiple birds; however, it is a new vaccine and it may be prudent to wait for the initial reports of its use in the general population.

Psittacine Wasting Disease (Macaw wasting disease, proventricular dilation syndrome), is another disease entity that is thought to be viral in origin, (this has not been scientifically proven yet). Seen most commonly in the large Macaws, it initially presents as a bird with vomiting or regurgitation, passage of undigested seed or other food, and other gastrointestinal signs. The birds are frequently very depressed and over a short period of time become progressively more weak as they loose weight. Currently, diagnosis requires a biopsy of the stomach, yet certain radiographic signs may be suggestive of the disease. Even with extensive supportive care almost all affected birds will die from this disease. Researchers are trying to confirm that this is a viral disease and assess how infectious it is.

Pox Virus is a disease that has become less common as more birds are raised domestically and less birds are imported. This viral disease use to be very common in imported Blue-fronted Amazons, yet is currently only seen sporadically in birds other than canaries and finches. The most common presentation involves skin lesions around featherless areas of the head, particularly the eyelids. Small nodules and scabs may be seen which in severe cases may result in a lot of swelling and inflammation. The virus is shed in the scabs and this is turn results in environmental contamination with the virus. The virus needs a break in healthy skin to start an infection; this may be a small wound or the result of some insect bite where the insect can transmit the infection from bird to bird. Insect transmission is probably a major factor for birds in outdoor aviaries. In most cases, these cutaneous forms of pox are self-limiting and the birds will recover with only some residual scarring. There is also a more aggressive form of the disease which involves the upper respiratory tract; in these cases the infection may result in the death of the bird due to swelling and inflammation of the breathing passages. Treatment can limit the secondary problems seen with pox infections. A vaccine is available for the canary pox, and another vaccine was available for the amazon pox, yet it is currently difficult to get. Keeping birds indoors and isolated is the best preventative measure.

BACTERIAL INFECTIONS

There are a number of different bacterial infections that birds commonly get. In most cases the birds are probably susceptible to these infections due to underlying problems that have allowed for a large bacterial population to overwhelm their normal immunity, or the birds themselves are already weakened due to stress, poor nutrition, or poor husbandry. A healthy bird on a good diet will only rarely get a bacterial infection. The normal bacterial population on a bird is different from humans, so some of the bacteria that humans normally carry, such as E. Coli, can cause infections in birds. (This is the reason behind the recommendation to not allow a bird to take food from the owner's mouth.) If one considers what an excellent medium for bacterial growth decaying food and fecal matter at room temperature are, it is also easy to appreciate the importance of frequent and thorough cage cleaning and disinfection. Bacterial infections can affect any of the organ systems, yet the most common infections affect the upper respiratory tract or sinuses, the intestinal tract and liver, the urinary tract, the reproductive tract, and the skin and feather follicles.

Upper respiratory tract infections will present with sneezing, nasal discharge, inflamed eyes, and if it also involves the sinuses, there will be swelling of the head around the eyes. These infections can vary from relatively mild conditions that owners will frequently characterize as "colds" to very severe problems where the bird has difficulty eating and breathing and requires hospitalization. Once the bacterial infection is diagnosed and the antibiotic selected by a culture and sensitivity, treatment may vary according to the severity of the infection and which parts of the upper respiratory tract are affected. Simple infections may be treated with oral antibiotics and drops for the nares and eyes. More severe infections involving the sinus will require more aggressive treatment which may include sinus flushes, nebulization, and sometimes surgery. Recurrent sinus infections are particularly difficult to treat and eliminate, much to the frustration of both the owner and the veterinarian.

Infections involving the intestinal tract and/or the liver frequently present as a bird that has lost its appetite, may be vomiting or regurgitating, most commonly has a change in the droppings with diarrhea seen frequently, and may also be quite depressed. These infections can come on quite quickly and be fairly severe in many cases. Contaminated or spoiled food is a likely source of infection for these patients. Bacterial culture and sensitivity of the feces allows for the selection of the right antibiotic, and blood panels will determine the extent and severity of the liver involvement. If caught early and treated aggressively, most patients will respond as long as they are not too debilitated due to other problems. Seriously ill birds will require supportive therapy such as fluids for dehydration, incubation to maintain body temperature, and tube feeding if not eating on their own.

Urinary tract infections can present as a bird that is drinking large amounts of water and who has runny droppings due to all the liquid in the droppings. These birds may also be loosing weight in spite of eating normally. If a urinary tract infection is allowed to persist it may cause permanent kidney damage. Severe kidney damage can be detected with a blood panel and the associated increase in the uric acid level. High uric acid levels can cause problems such as gout which is a severe condition and very difficult to treat. Urinalysis can be done on birds to detect early urinary tract problems, yet is difficult in many cases due to the problem of collecting a sample that is not contaminated extensively with feces. Treatment of mild urinary tract infections is normally straight forward.

Reproductive tract infections are of greatest concern to bird breeders. Most pet birds that are not sexually active or laying eggs will only rarely have a problem. This problem is seen in breeding birds as problems associated with egg laying, the fertility of the eggs, or with neonatal infections. If the infection is detected in the egg or young chick, it can frequently be traced back to the hen. Examination of the eggs, examination of the reproductive tract with endoscopy, and bacterial cultures will allow for a definitive diagnosis. Diagnosis and treatment will frequently correct the problem, yet in some cases the infection has resulted in permanent damage and a loss of fertility where the bird, or breeding pair should be removed from a breeding program.

Bacterial skin infections most commonly present as a bird that is picking excessively and loosing too many feathers. Occasionally skin infections may be apparent on physical examination as inflammation or redness around the feather follicle. Culture of a feather follicle, or of a feather bulb, is the best means of confirming this condition. Unfortunately, only a small number of feather pickers have a bacterial infection as their primary problem. When bacterial skin infections are present they are normally responsive to antibiotics.

It should be pointed out that the various over-the-counter antibiotics sold by pet stores are almost invariably useless since most bacteria are resistant to them. Since these are most commonly mixed in the drinking water, accurate dosing of the birds is very difficult, and in many cases the medication has a flavor which the bird dislikes, so they drink less water than they should, adding another stress factor to the already sick patient. Antibiotics should be directly administered to the bird either as a oral medication directly into the mouth or crop, or as injections. For most owners it is not that difficult to learn how to give injections, and many times this is the simplest and least stressful way to medicate a bird.

Some bacterial infections that birds get are thought to be transmissible to man. The most important bacterial agent that is a human risk is mycobacteria or tuberculosis. Birds can carry M. tuberculosis, the human form of tuberculosis, and M. avium, the avian form of tuberculosis which is transmissible to man. While these infections are not common in most species of birds, it must still be kept in mind, since these diseases are very difficult to treat and potentially devastating for both man and bird. Humans with immunosuppresion due to conditions such as AIDS or cancer, should be particularly careful about exposure to birds that may be carriers of zoonotic diseases, (diseases transmissible to man). Birds with the human form of tuberculosis most likely get it directly from a infected human with which the bird had close contact. The avian form of tuberculosis can be spread from bird to bird, and it can be contagious to humans. The treatment of tuberculosis in birds is highly controversial due to the human health risk. It should be kept in mind that total elimination of the infection from the bird is probably impossible to prove, and thus the bird should be considered a carrier for the rest of its life. Also, any birds exposed to the diagnosed bird should be considered to be carriers even though they may not show any clinical signs. Diagnosis of tuberculosis is difficult and frequently requires a biopsy, either from a live patient or at necropsy. Tests available for screening birds are limited to microscopic examination of the feces for the presence of the tuberculosis bacteria, and this is not very good at picking up infections.

PSITTACOSIS, CHLAMYDIOSIS, ORNITHOSIS, PARROT FEVER

These are all the same name for an infectious disease caused by a chlamydial organism, a life form that doesn't fit into the classification of either a bacteria or virus. Psittacosis refers to the organism whose natural host is psittacine birds, and for the intent of this discussion, we will use this term. Chlamydiosis is a general term that refers to infection of all birds and other animals including man. It should be noted that there is a chlamydial infection specific to humans which is a common venereal infection; that is an infection distinct from that seen in birds. Psittacosis is seen in all psittacine birds, although some such as cockatoos, are much more resistant to infection. It is a zoonotic infection, and as such, owners of birds should be aware of their potential health risk.

Psittacosis can present with a variety of symptoms including upper respiratory with runny eyes, sneezing, and congestion. Respiratory infections with airsac involvement are also seen, and this can cause difficulty breathing. Liver disease is one of the more severe presentations and can progress rapidly to death. Another important factor regarding psittacosis is that it can incubate as an asympotomatic infection for years; thus a bird that has appeared healthy in the past can suddenly develop symptoms and become ill. The variety of symptoms and the potential for a lengthy incubation period means that this disease must always be considered when evaluating a sick bird. Blood panels in psittacosis birds can show certain characteristics which are suggestive of the infection, yet a conclusive diagnosis cannot be made based on a panel alone. In most cases the diagnosis is made by identifying the organism in the feces, yet even birds with an active case only shed the organism intermittently, so the psittacosis test cannot detect all cases of the disease. If a suspected case dies, then the best test is a necropsy and pathology on the liver and spleen.

The disease is spread via feces, as well as being airborne, so it is highly contagious. To make the problem even worse, birds that are not clinically ill may also shed the organism. All these factors make the disease difficult to control in an aviary situation. Most aviaries institute rigid isolation protocols, as well as screening birds with a fecal psittacosis test prior to adding them to a collection. These same techniques should be utilized by the average bird owner to protect themselves and any birds they may have. While the psittacosis test that is most commonly used currently is by no means an ideal test, it still is prudent to screen birds for the disease, particularly with the potential for human infection.

In most human infections, psittacosis normally causes relatively mild signs that are frequently described as being flu like. Fevers, headaches, joint discomfort, and respiratory signs are often reported by humans infected from birds. However, the disease does have the potential to be much more serious, and can cause death in extreme cases. People with suppressed immune systems are at greatest risk, and some physicians advise their patients not to be exposed to birds due to the risk. Because of the human health risk, cases of psittacosis in birds must be reported to the local health authorities, who in turn take steps to assure that the disease is contained and that further human exposure is minimized. Exposed bird populations are quarantined and must go through a treatment protocol to eliminate the infection. Treatment of infected or exposed birds is with a tetracycline based antibiotic which must be given for a total of 45 days to eliminate the carrier state. Even with the full treatment it is possible to have a relapse infection, and some avian veterinarians are of the opinion that our current treatment protocols do not eliminate the carrier state in many birds.

The diagnosis and treatment of psittacosis is one of the most controversial aspects of avian veterinary medicine, as well as with many aviculurists. It is an area of intense research and will probably be changing constantly.

FUNGAL/YEAST INFECTIONS

Aspergillosis is a fungal infection that is seen in most species of birds. It is considered an opportunistic infection; the infectious organism is wide spread in almost all environments, so all birds are exposed to it; yet, only birds with immunospression or other problems get an active infection since they are normally able to control it. Chronic illness, malnutrition, and inadequate housing BG are all factors in predisposing some birds to an infection. Unfortunately, the structure of the avian respiratory system supplies a perfect incubator for growing a fungus such as aspergillosis-- the airsacs. The airsacs have almost no blood supply, so once aspergillosis gets started in the airsacs, it can continue to grow. There are several situations where the psittacine birds are most likely to be exposed to the greatest risk of aspergillosis. One is with hand-fed chicks where they can aspirate some of the feeding formula into their airsacs, which then acts as a foreign body where the fungus can start to grow. Breeding birds that spend a lot of time in nesting boxes are also at risk since many of the commonly used substrates in nesting boxes offer the perfect medium for growing the fungus which the birds then breathe in within the tight confines of the nest box. Chronic antibiotic therapy that lowers the birds immune system and disrupts the normal microbiological flora of the bird may also allow for a secondary aspergillosis infection. In birds that are identified as being at risk of an infection, a preventative treatment can be started which is very effective at preventing the infection. Basic husbandry and nutrition must be evaluated and problems corrected to also help prevent the disease. Active infections are normally diagnosed via radiographs, endoscopy, and fungal cultures. Many cases are not detected until a necropsy is performed; the birds may have an asymptomatic infection for years. Treatment is difficult and must be done for 6 months or longer to eliminate the infection.

Candida is a yeast that can cause infections in the mouth, crop and occasionally the rest of the intestinal tract. It is most commonly seen in young chicks, particularly those that have been treated with antibiotics, which disturb the normal bacterial balance. The infections can be detected as whitish plaques in the mouth, which reveal the yeast when examined microscopically. The birds will often be hesitant to eat due to oral soreness, or they may have slow emptying of the crop. Failure to gain weight is a common complaint in young chicks. The candida infection is normally easily treated with an oral medication. Candida is not considered to be highly contagious; however, if the same equipment is used among different chicks during hand-feeding, transmission of the infection could occur. This infection is most commonly seen in cockatiels. Yeast infections have also been associated with skin infections which can lead to excessive feather picking; this can be detected with feather biopsies or feather pulp microscopic examination. Cutaneous yeast infections are more difficult to treat.