Pediatric Avian Medicine: Infectious Diseases of the Psittacine Chick

Key Points

  • Gram-negative bacteria and non-budding yeast may be normal findings in the gastrointestinal tract, but these organisms can quickly overgrow and cause disease in the stressed juvenile bird.
  • Avian polyomavirus is the most devastating disease that can affect the psittacine nursery. Depending on age and species, the clinical picture may include peracute death, coelomic distention, subcutaneous hemorrhage, abnormal feather formation, non-specific signs of illness, delayed crop emptying, regurgitation, diarrhea, dyspnea, posterior paresis or paralysis, and polyuria.
  • Psittacine beak and feather disease may also affect a variety of species. Clinical signs may include non-specific signs of illness and dystrophic feather formation. Immunosuppression can lead to septicemia and secondary pneumonia, enteritis, and death.
  • Two important infectious causes of regurgitation and crop stasis in the chick are candidiasis, and avian polyoma virus. Candida spp. is an important cause of disease that is easily managed if recognized early, while there is no real specific treatment for polyoma virus, which is often fatal.

Normal flora

Microbial flora of the psittacine gastrointestinal tract includes Gram-positive organisms such as:

  • Lactobacillus
  • Bacillus
  • Corynebacterium
  • Streptococcus
  • Micrococcus spp.
  • Staphylococcus epidermidis
baby bird Rivera

Gram-positive bacteria make up the majority of the normal gastrointestinal flora of the psittacine bird. Photo credit: S. Rivera

The presence of non-budding yeast like Candida albicans can also be normal in the gastrointestinal tract.

Microbial infections of the gastrointestinal tract and associated organs

Unfortunately Candida spp. can quickly overgrow and become a primary problem in the stressed juvenile. Clinical signs may include anorexia, white oropharyngeal plaques, delayed crop emptying, and regurgitation.

Potential causes of bacterial enteritis include Escherichia coli, Klebsiella, Enterobacter, Pseudomonas, and Salmonella spp. Gram-negative bacteria may be isolated from healthy juveniles, and, as a general rule, their presence does not require attention unless abnormal clinical signs such as anorexia, diarrhea, or weight loss are observed. Immediate, aggressive antimicrobial therapy and supportive care are essential for a successful outcome as bacterial enteritis may lead to septicemia and death.

Intussusception may develop in some birds with enteritis. Common signs include diarrhea or fresh blood in the stool. Intussusception may also lead to cloacal prolapse in some cases. Confirm this diagnosis with contrast radiography or ultrasonography, and correct the defect surgically. The prognosis for full recovery is guarded to poor. In many cases, the patient is severely compromised by the time a diagnosis is made.

 

Psittacosis

Chlamydophila psittaci infection in parrot chicks can lead to serious illness and death if not treated promptly. Clinical signs may include lime-green stools, nasal discharge, and diarrhea. Secondary overgrowth of gram-negative bacteria and yeast is common. Diagnosis is based on the same principles as adults, however serologic testing is unreliable in young birds due to their immature immune system and inability to mount a strong immune response.

Viral diseases affecting juvenile parrots

Polyomavirus

Avian polyomavirus (APV) is the most devastating disease that can affect the psittacine nursery. APV was first described in budgerigar parakeets (Melopsittacus undulatus), but disease can affects a wide variety of birds. Virus can be transmitted vertically or horizontally.

Clinical signs vary depending on the species and age of the affected bird.

  • Lethargy, weakness, anorexia, weight loss, dehydration
  • Delayed crop emptying, regurgitation, diarrhea
  • Abdominal distention
  • Subcutaneous hemorrhage
  • Abnormal feather formation (rarely seen in large psittacine species)
  • Dyspnea
  • Posterior paresis or paralysis
  • Polyuria

The mortality rate can be extremely high. Budgerigar parakeets and large parrot chicks may die peracutely. Some young birds die shortly after the onset of clinical signs. Chronic disease is characterized by abnormal feather formation, recurrent bacterial and/or fungal infection, weight loss, anorexia, and polyuria.

Diagnosis is based on history, clinical signs, DNA-based tests, and histopathologic evaluation.

I have seen APV outbreaks linked to the introduction of apparently healthy chicks into the nursery from a different source. Basic quarantine protocols could have prevented these outbreaks. The APV vaccine has also decreased the incidence of disease. Vaccinate adults prior to the onset of the breeding season. Vaccinate chicks according to manufacturer instructions.

Proventricular dilatation disease

Proventricular dilatation disease (PDD) has been reported in a wide variety of psittacine birds. In juveniles, clinical signs include depression, regurgitation, undigested formula in the feces, ataxia, head tremors, and seizures. Definitive diagnosis is based on the identification of lymphocytic-plasmacytic ganglioneuritis within the gastrointestinal tract. Crop biopsy is the best antemortem test, however this technique has a 24% false negative rate and a negative result cannot rule out PDD.

PDD may theoretically be introduced into the nursery by asymptomatic offspring of affected parents. When birds are discovered in the nursery with PDD, isolate and closely observe the parents. Remove birds known to be positive for PDD from the breeding program. Since the cause of PDD is unknown*, there is currently no reliable test to screen birds for PDD.

*Editor’s note (7/12): Avian bornavirus has been confirmed as a cause of PDD in birds.

Psittacine beak and feather disease

Psittacine Beak and Feather Disease (PBFD) is caused by a circovirus. This virus affects a wide variety of birds and has been reported in over 30 parrots. Beak and Feather Disease is most commonly seen in Old World species like the African Grey parrot (Psittacus erithacus) and cockatoo.

  • Birds with peracute infection suffer from septicemia that leads to pneumonia, enteritis, and death.
  • Acute illness is characterized by depression and the development of abnormal feathers as the down coat is replaced.
  • Chronic disease is more common in adult birds and is characterized by the development of dystrophic feathers with each successive molt.
  • PBFD leads to the destruction of lymphoid cells in the thymus and bursa of Fabricius. Immunocompromised birds usually succumb to secondary viral, bacterial, or fungal infections.

Beak and Feather Disease is transmitted through the ingestion or inhalation of contaminated material such as body secretions and feather dust. Vertical transmission is also suspected. Diagnosis is based on physical examination and DNA testing of blood, feces, or crop secretions. Histopathologic examination of affected feathers and/or feather follicles may reveal intracytoplasmic inclusions.

Since the halt of wild caught bird importation as breeding stock, the incidence of PBFD outbreaks in the psittacine nursery is declining, however, clinical disease is still prevalent. In my experience, PBFD is most commonly seen in lovebirds.

Signs of infectious disease

Depending on the etiologic agent and anatomic region involved, infectious disease can manifest in a variety of ways. Two common problems observed the chick include crop stasis and stunting.

Stunting

Stunting is commonly seen during the first month of life and may be associated with poor husbandry practices or an underlying infection. Stunting may be characterized by:

  • Poor growth rate
  • Failure to thrive
  • Low weight
  • Thin limbs
  • Large head relative to body size
  • Delayed or abnormal feather growth
  • Delayed eye and ear opening in some cases
  • Eye slits open dorsal to the horizontal midline of the orbit

Some chicks appear healthy but have an abnormal weight for their age and gain weight at a slower rate. If caught early, correction of the underlying problem(s) may reverse stunting.

Crop stasis

Delayed crop emptying is one of the most common problems seen in psittacine chicks. More often than not, improper management causes crop stasis, but it may also be caused by Gram-negative bacterial and/or yeast within the gastrointestinal tract.

If not treated promptly and aggressively, crop stasis can lead to severe dehydration, septicemia, and death. The first priority is to clean the crop and initiate supportive care. In some cases oral fluids can be used to soften inspissated crop contents, which may then be removed through a feeding tube. Repeat this procedure several times until the crop is clean, but take care when aspirating crop contents. The crop wall is fragile and can be damaged by aggressive suction.

Diagnostic tests should include crop cytology and culture. Complete blood count (CBC), biochemistry panel, and whole body radiographs will help in evaluation of the overall condition of the bird.

Once the crop is emptied, give a small amount of fluid by tube and wait a few hours before feeding. Metoclopramide (0.5 mg/kg IM initially, then PO every 8 hrs) and cisapride (0.5 mg/kg PO every 8 hrs) can be used as gastrointestinal motility stimulants. (See Crop Stasis in Birds for more information on this condition).

 

Summary

Although Gram-negative bacteria and non-budding yeast may be normal gastrointestinal flora in the psittacine bird, these organisms can quickly overgrow in the debilitated chick. Signs of clinical disease can first manifest as crop stasis or stunting. A wide range of agents can cause problems, however important infectious diseases in the juvenile psittacine bird include avian polyomavirus, psittacine beak and feather disease, and candidiasis.

References