Some Facts about Psittacosis

Even though psittacosis has been described in both birds and humans for many years, it was positively identified for the first time in 1879. Until 1930, psittacosis, or "parrot fever," was thought to primarily infect the large parrots. However, in 1929 and 1930, a pandemic of psittacosis occurred, infecting both humans and non-psittacine birds. This world-wide epidemic was precipitated by the shipment of large numbers of amazon parrots from Argentina to numerous locations throughout the world. As a result of this pandemic, the United States and many other countries imposed a total ban on the importation of birds. The United States partially lifted this ban in 1967 and, in 1973, this importation ban was completely removed.

From 1942 through 1964, psittacosis outbreaks were described in non-psittacine bird populations, including pigeons, ducks, geese, pheasants, turkeys, and occasionally in hawks. Psittacosis is also found in wading birds and shore birds such as herons and egrets, and in many sea birds such as gulls, terns, and fulmars. Psittacosis, or "ornithosis" as it is commonly referred to when this organism infects bird taxa other than parrots, has been positively identified in at least 140 avian species. This finding has led many experts to believe that all bird species are capable of being infected by this organism.

Psittacosis infections are not limited to birds. Surprisingly, the "psittacosis organisms" were found to infect many vertebrate species, including humans, sheep, cattle, horses, goats, dogs, cats, most rodent species, and even frogs. These infections are not uncommon: Until recently, this group of infectious organisms has been documented to be the main cause of "nonspecific pneumonitis" in domestic cats, and it continues to be one of the main causes for spontaneous abortions in sheep. In fact, this large host range and wide variety of symptoms led some researchers to speculate that there were several species of organisms that caused "psittacosis"-like infections.

Due to this wide host range, and also because of the wide variety of symptoms and the large number of closely-related species described, psittacosis is known by many names, including "ornithosis," "parrot fever" or "parrot disease," and "ornithotic pneumonia." Other, more quaint names include "one-eyed roup" when it causes "pink eye," or conjunctivitis. However, the medically correct term for describing a bird that is infected with this organism and showing symptoms of the disease is "chlamydiosis." Infected but asymptomatic carrier birds are described as having "chlamydiasis" (I will use the word "psittacosis" in this article when referring to both states. Otherwise, the technically correct name will be used when I intend to refer specifically to one disease state and not to the other).

Chlamydiosis is the disease caused by a group of closely-related organisms with a very small size that belong to the bacterial family Chlamydiaceae. Originally, the organisms that cause psittacosis were classified as a variety of strains within the species, Chlamydia psittaci, until recent research by Karen Everett at the University of Georgia revealed that the genus, Chlamydia, should be split into two genera, instead. At that time, those many strains of organisms that cause "psittacosis" were subsequently reclassified from many strains within one species, and elevated into separate species within their own genus, Chlamydophila. Each Chlamydophila species was named for the animal species that is primarily associated with it, for example, C. felis is primarily found in cats and C. suis is associated with pigs. However, many or perhaps all of the Chlamydophilae (the -ae ending is plural) can infect species other than those for which they are named and mainly associated with.

The Chlamydophilae organisms are very odd: they are obligate intracellular parasites, meaning that they must directly invade host cell and steal nutrients from that cell in order to reproduce. The Chlamydophilae are "energy parasites" because they are incapable of generating their own energy stores from available nutrients but instead, they obtain energy by pilfering it directly from their host cell. In contrast, typical bacteria can produce their own energy by intercepting food molecules before these molecules enter (and can be metabolized by) the hosts' cells.

Historically, the Chlamydophilae were thought to be large viruses because of their small size and their unusual and complicated life cycle. As previously mentioned, the most notable aspect of this unusual life cycle was the Chlamydophilae's total dependence upon directly invading its host cell. In fact -- similar to viruses and unlike bacteria -- it cannot reproduce outside of its host cell. However, like bacteria, the Chlamydophilae are sensitive to certain antibiotics. Further research has shown that the Chlamydophilae are "primitive bacteria" and some researchers think that the Chlamydophilae occupy an evolutionary position between viruses and "typical" bacteria.

The life cycle of the Chlamydophilae are characterized by two distinct forms: the intracellular form (also known as the "initial body") and the infective form (also known as the "elementary body"). The large and fragile intracellular form is the reproductive stage of this organism. It reproduces by stealing essential molecular building blocks from its host cell so it can produce more Chlamydophilae organisms. Thirty-five to 40 hours after infection, the host cell has produced as many of these new Chlamydophilae as it can hold. At this point, the weakened and starving cell bursts open and dies, releasing hundreds of infective organisms into the animal's body. These newly-released Chlamydophilae -- the tiny and highly infective "elementary bodies" -- then invade nearby cells and continue their life cycle by producing hundreds more "offspring" that infect more naive host cells. When the sick animal coughs, sneezes, or defecates, it sheds these infective Chlamydophila into the environment. Other animals then become ill when they inhale or ingest these organisms. The entire life cycle is completed within 48-72 hours.

It is thought that when Chlamydophila is in the infective stage it is very difficult to kill. The elementary body is very resistant to drying and thus, it is capable of lying dormant in the environment for many months. It can be destroyed by quaternary ammonia compounds such as a 1:1000 dilution of Roccal-D or Zephiran. Other cleaning agents that are effective include 1:100 dilution of household bleach or a 1:100 dilution of Lysol. When an infected bird is actively shedding Chlamydophila, the vast majority of these liberated organisms will be in the highly resistant, infective form.

As previously mentioned, there are several other species of Chlamydophila, all of which can cause some nasty diseases in their hosts. Chlamydophila pneumoniae is a member of this genus that was discovered more than 20 years ago when it was found to cause a virulent pneumonia in humans. C. pneumoniae has also been implicated in human heart disease. Further, it can also infect birds.

In the wild, psittacosis is mainly a disease of nestlings and young birds. The incidence of psittacosis in wild adult parrots is less than 5%. After capture, however, the incidence of psittacosis approaches 100% due to the effects of poor nutrition, overcrowding, and other stresses. In captive birds, more than 50% of all cases of psittacosis are diagnosed in newly-purchased parrots -- those birds that have been in the owner's possession for less than 6 months. Many bird species commonly harbor asymptomatic infections of Chlamydophila species (chlamydiasis), such as starlings and rock doves (feral pigeons). In fact, these birds are thought to be primarily responsible for spreading this disease to parrots that are kept and bred in outdoor flights throughout the year, particularly those birds that are ranched in southern states, such as Florida.

As previously mentioned, Chlamydophilae have been found in many other species of animals such as guinea pigs, mice, sheep, goats, cattle, and horses. They cause miscarriages in sheep, cattle, and goats, and they contribute to respiratory disease, enteritis (inflammation of the intestines), conjunctivitis (inflammation of the eye tissue, or "pink eye"), arthritis, reproductive disorders and sterility in other mammals. In domestic cats, Chlamydophila species once commonly caused pneumonitis -- a pneumonia-like disease -- although (perhaps another species?) it can also result in conjunctivitis and a runny nose. Surprisingly, Chlamydophilae have also been found in insects, such as fleas, ticks, and lice. The role that they play in insects is unclear at this point but it has been speculated that these insects may be capable of transmitting this disease organism to other animals.

Psittacosis can spread rapidly through direct contact with infected birds or through ingestion of foods that have been contaminated by feces and other infectious materials produced by sick birds. However, Chlamydophilae are most commonly spread through the inhalation of feather dust, aerosolized feces, or infected droplets produced by sneezing or coughing birds. Even though psittacosis can spread very rapidly through a flock of birds, the disease is not easily transmitted by non-avian hosts, and documented human-to-human transmission is very rare, indeed.

Since psittacosis can be transmitted from infected birds to humans, it is classified as a zoonosis. Due to the potentially serious nature of this disease, psittacosis is a "reportable disease" in the United States, meaning that your doctor or veterinarian is required by law to report all positive diagnoses of this disease to the local health department. The health department then reports all incidences of reportable diseases to the Center for Disease Control (CDC), which maintains a constant vigil over potential threats to the public health. If there is evidence of a local or regional epidemic, the CDC will alert local health officials, who then search for the source of the epidemic. Once the source of the epidemic has been located, officials then quarantine that area and require the owner of the facility to provide proper medical treatment for all birds on the premises. Since psittacosis has already caused at least one pandemic and numerous smaller epidemics, it is necessary to monitor the incidence and spread of this disease.

Approximately 100 cases of human psittacosis are reported annually in the United States, and one person may die from it each year. Those people who are most susceptible to infection are those whose immune systems are not functioning with maximal efficiency; infants and toddlers, people over 50 years of age, smokers, alcoholics, and immunocompromised individuals such as college students and people with AIDS. The highest risk categories for infection include pet bird owners and employees of the pet bird trade, followed by bird fanciers, family members of bird owners, pigeon fanciers, and poultry producers and fanciers. In fact, the CDC reports that 70% of all human psittacosis cases that had a known source for infection resulted from exposure to a caged bird.

One of the worst aspects of psittacosis is the difficulty in recognizing and diagnosing this disease. In birds, psittacosis produces a large number of symptoms, ranging from nearly asymptomatic to very serious. (These differences in disease severity might be due to infection with different species of Chlamydophila, but this remains unknown at this time). Some asymptomatic birds can breed while infected, although they will usually have a high number of infertile eggs or a high mortality among their nestlings. In spite of these seemingly mild consequences, psittacosis can also be quite serious. It is not uncommon for birds to become very ill and die within one week of exposure, leaving the pet owner with very little warning as to the severity or the nature of the disease itself.

Several factors affect the severity of symptoms exhibited by infected birds. The severity of the symptoms depends not only upon the bird's age and its general health, but the route of infection is important. When the bird is infected via inhalation of the organism, the disease gains direct entry into the bird's lungs and infection can progress more rapidly than if ingested in contaminated food or water.

Severity of the resulting illness also depends upon the species of Chlamydophilae that has infected the bird. Some species are quite virulent and cause rapid progression of symptoms within a very short time span, while other species of Chlamydiophilae result in a mild, chronic infection that is barely noticeable.

The species of bird that is infected with Chlamydophilae also affects the severity of disease symptoms. Some bird species are more susceptible to these disease organisms than others. These more susceptible species -- generally macaws and amazons -- usually have a shorter incubation time and exhibit a more rapid progression of the disease, with more severe symptoms, than those seen in less susceptible parrot species, such as African Grey Parrots.

The Chlamydophilae show a strong affinity for mucous membranes and readily invade the cells that comprise these mucous membranes; the eyes, nasal passages and lungs, respiratory and reproductive tracts, and the intestines. Once infection has occurred, Chlamydophilae can quickly escalate their attacks to include all organ systems of the body, particularly the kidneys, liver, heart, and brain. After a successful infection has occurred, massive numbers of dead and dying cells are shed into the environment as the bird suffers from diarrhea, sneezing, and pneumonia. Other symptoms include anorexia, lethargy, runny nose and eyes, and fluffed feathers. When left untreated, the bird will usually die of malnutrition, dehydration and the effects of resulting electrolyte imbalances, or from pneumonia. If this disease is not treated quickly enough, the bird suffers from extensive damage to its internal organs. This damage may be permanent even when the bird has survived the ravages of the disease itself.

In birds, the incubation time -- the time span from initial exposure until symptoms are first apparent -- ranges from 5 to 96 days. The average incubation time is 4 weeks, although some sources claim that a bird may incubate the disease for as long as ten years before stress or some other factor causes overt symptoms to develop. This prolonged incubation time is quite rare, however.

Infected humans -- similar to infected birds -- can also display mild or severe symptoms. Ornithosis or chlamydiosis (as the disease is usually referred to when it infects humans) usually manifests itself with flu-like symptoms. These symptoms range from acute fever and headache to a life-threatening pneumonia. The incubation period in humans ranges from 5-14 days and the symptoms persist for 7-10 days, although some patients feel lethargic and experience frequent, severe headaches for many months after successful treatment. If untreated, the mortality rate in humans is 20-23% but, with proper diagnosis and treatment, mortality is less than 1%.

Immunity to Chlamydophilae is not long-lived and re-infection is very likely when all birds have not been properly treated. This lack of a strong immune response is probably due to several factors. First it is likely due, in a large part, to the life cycle of the organism itself. Since Chlamydophilae are hidden inside their host's cells, the host's body cannot see the invading organisms in order to mount a strong and long-lived immune response. Second, there are many species of this organism, which makes it difficult for the immune system to recognize them all well enough to mount an effective immune response because each species "looks" different to the immune system. Thus, each infection with a new species results in the host's immune system responding as it would if it was encountering this disease organism for the first time.

Diagnosis of psittacosis is not easy because of its ability to "hide" within its host cell, the large number of species that can be the cause of the infection and also because of the large range of symptoms that these species cause. In fact, there is no single diagnostic test that will give 100 percent reliable results. Thus, it is imperative that the veterinarian perform at least two different diagnostic tests to verify the presence of this organism.

There are a wide variety of methods used to definitively diagnose this disease in pet birds. These tests include; detecting Chlamydophilae DNA in blood or feces using Polymerase Chain Reaction (PCR), isolation of Chlamydophilae organisms from a clinical specimen and successfully growing it in culture, fluorescent antibody (FA) detection in a tissue sample, detection of the organism using ELISA (enzyme-linked immunosorbent assay) from fecal samples or cloacal swabs, visual identification of Chlamydophilae organisms in macrophages (one of several types of white blood cells) obtained from a blood or tissue sample, or a four-fold or greater increase in the bird's serological antibody titre from paired samples obtained at least two weeks apart. Additionally, the complete blood count (CBC) can be a valuable clinical tool because psittacosis causes specific changes to occur in the bird's blood before symptoms become apparent. Using a CBC as part of the diagnostic process can greatly enhance the value of other, less reliable, tests.

When attempting to diagnose a seriously ill bird that demonstrates chlamydiosis-like symptoms, it is best to collect the necessary specimens required for the confirmatory laboratory tests before treatment is initiated, since antibiotics can interfere negatively with these diagnostic tests. After these specimens have been collected, treatment should begin immediately.

Diagnosis in humans isn't nearly so difficult, provided that you tell your doctors that you have been associating with birds. Ornithosis is an exotic disease and, due to this fact, doctors may not think to ask about exposures to birds until all other treatments have been attempted without success. The most typical method of diagnosing psittacosis in humans is by isolating it from a culture obtained from a sputum, pleural fluid, or serum sample. Serological testing methods, such as a serum ELISA test, may be used in addition to a culture-positive test. However, if the patient has been in close contact with psittacosis-positive birds, and has successfully fought off infection, the ELISA can yield a false positive result. Thus, this test must be used in conjunction with other, more definitive, tests. Occasionally, some doctors will diagnose psittacosis by using a chest x-ray, particularly if the patient is acutely symptomatic. Fortunately, once diagnosed, this disease is very responsive to proper antibiotic treatment, and a full recovery usually occurs quickly.

Psittacosis is easily treated if it is caught before extensive tissue and organ damage has occurred in birds. It is very responsive to treatment by the tetracyclines. However, these treatments are not guaranteed to be completely safe or effective for all avian species. Some drawbacks associated with these treatment regimens follow;

The United States Department of Agriculture (USDA) has approved a 45-day regimen of oral chlortetracycline (CTC) for use in recently-imported birds that are in quarantine. However, since the USDA does not have jurisdiction over psittacine species once the birds have been released from quarantine, nor do they have any control over domestically-produced parrots, this "approved treatment regimen" is almost irrelevant. Additionally, since the importation of wild-caught psittacines into this country almost stopped about ten years ago, it is quite unusual for a wild parrot to legally enter this country. Therefore, the CTC-regimen is not commonly used. However, some basic information regarding this treatment method is provided, should you use it to treat a sick bird.

CTC is usually administered via CTC-impregnated (1%) pellets for larger parrots or CTC-coated millet seeds (0.5 mg CTC/gm seed) for smaller birds. There are several problems associated with using CTC that the pet owner should be aware of. The first is its unpleasant taste, which causes many parrots to refuse the medicated feed. Second, this drug tends to kill beneficial gut bacteria which can result in a fungal infection and overgrowth, especially with Candida. Third, CTC binds to calcium, thus destroying the drug's effectiveness while simultaneously interfering with calcium absorption from the gut. Last, CTC can cause permanent damage to the bird's kidneys. (Note that the USDA does not have any jurisdiction over pet birds regarding Chlamydiophilae treatment after the quarantine period has been completed. Due to the severe restrictions on importation of birds into the USA, most birds that are available to the pet trade have never undergone the required quarantine period nor have they been tested for Chlamydophilae. Thus, one should never assume that a pet bird is free from this organism unless it has been thoroughly checked by a licensed veterinarian.)

Unless the bird is particularly difficult to handle, the best method of treatment is oral administration of doxycycline (doxy). This medication was originally developed for use in humans and is listed as the drug-of-choice for treating psittacosis in parrots. The reasons for recommending doxy are many; it maintains a therapeutic blood concentration for longer periods of time than does CTC, it is gentler on the kidneys than CTC, it doesn't interfere with absorption of calcium as much as does CTC, it causes fewer gastrointestinal upsets, and it doesn't destroy all of the normal gut flora. The dosage of this drug varies between different species, a fact that your veterinarian should be aware of when prescribing it. Doxy is usually administered orally, however, an injectable form of doxy is available to your veterinarian from Europe (this form of doxy is available only to veterinarians in the United States that have a special INAD permit with the FDA). Other forms of doxy are not suitable for injection at this time, and their use is strongly discouraged until further research has been completed. Doxy can also be administered in the bird's drinking water (unpublished data), although this form of delivery is quite unusual and may not be very effective if not supervised carefully by your veterinarian. (Please remember that other tetracyclines are not effective when administered in the drinking water, nor are they useful for treating psittacosis.)

There are several things that the pet owner must know when treating a bird for psittacosis. First, it is imperative to severely limit all sources of calcium in its diet, unless directed otherwise by your veterinarian. All calcium blocks and cuttle bones must be removed from the bird's aviary, and any vitamin supplements that contain calcium must be stopped. Tetracyclines tend to bind to calcium and thus, a therapeutic level of tetracycline will not be achieved, even when the bird is receiving adequate amounts of this antibiotic on a daily basis. Another thing to be aware of is, since the tetracyclines do bind to calcium, the calcium is no longer available for the bird's use. As a result, the bird's calcium levels will drop while undergoing any form of tetracycline treatment and the bird will be calcium-depleted. Calcium-depletion greatly increases the bird's risk of fatal egg-binding so all nest boxes should be removed or blocked off to discourage breeding attempts during treatment. Breeding birds should not be allowed access to the nest box until they have fully recovered from this disease and normal blood levels of calcium have been restored.

When treating a sick bird, a visible improvement will usually occur within a few hours to one day after medications have been administered. This improvement is usually observed as an increase in appetite as well as an increase in vocalization and activity. When you see this, do not be deceived! The tetracycline drug family cannot kill bacteria directly. Instead, tetracyclines are bacteriostatic: that is, they prevent bacteria from reproducing, but cannot kill them. The infection eventually is cleared from the bird's system because the bacteria cannot maintain their numbers without reproducing themselves. When the host cell dies, the Chlamydophilae that it contains also die, thereby slowly reducing the overall numbers of infectious organisms that remain within the bird's body. If you stop treatment early, you will be allowing the static Chlamydophilae to recover -- and to reproduce again.

As previously mentioned, Chlamydophilae can be very difficult to kill and appears to be capable of lying dormant in the environment for many months. It can be destroyed by quaternary ammonia compounds such as a 1:1000 dilution of Roccal-D or Zephiran. Other cleaning agents that are effective include 1:100 dilution of household bleach or a 1:100 dilution of Lysol.

Since psittacosis outbreaks are so intimately connected to the exotic bird industry, it is the responsibility of those who are involved with the pet bird industry to devise methods of controlling this disease and preventing its spread. Here are some minimal guidelines that breeders and retailers should follow, both for their own protection and for the protection of the general public.

1. Maintain accurate records describing all bird exposures. These records should include a brief description of the physical appearance of the bird, its band number, location, the owner's identity or the source of the bird. The movement of all birds on and off the premises and their general health at this time should also be recorded. All trips to the veterinarian, along with receipts and test results, should be maintained for each and every bird on site.

2. All birds should be banded or microchipped. In the case of a lawsuit, this method of identification will make your life much easier.

3. Use the correct treatment regimen and treat the birds for the full period of time. Also, have your veterinarian recheck recovered birds several weeks after their treatment has been completed to ensure full recovery.