Pacheco's disease is caused by a group of psittacine herpesviruses. There are at least three different psittacine herpesviruses that cause clinical and microscopic changes characteristic of this disease. It is probable that other variants of this virus will be identified in psittacine birds. Pacheco's disease is most common in homes with multiple birds and aviaries. The disease is rare in individual companion birds, unless they have recently been exposed to infected birds.
Most psittacine birds are considered susceptible to infection but disease may or may not occur depending on the strain of virus, route of exposure and species and condition of the infected bird. Birds that survive the initial infection are considered infected for life (latent infection) and can intermittently shed the virus. Latency is a type of permanent infection associated with some viruses, particularly herpesviruses.
Pacheco's disease outbreaks usually occur following stressful events or exposure of solitary birds to others that are shedding the virus.
What to Watch For
- Increased water consumption and urine output
- Difficulty moving
- Loss of appetite
- Yellowish or greenish discoloration of the urates and urine
- Sudden death in a bird that appeared completely normal hours earlier
The herpesviruses that cause Pacheco's disease are not known to infect humans or to infect other types of birds naturally.
- Complete blood count
- Blood chemistries
- Radiographs (X-rays)
- Serology (testing for antibodies)
- Culture for PDV
- DNA probe-based test (PCR) on choanal and cloacal swab
- DNA probe-based test (in situ hybridization) on tissues of birds with suspicious microscopic changes
Treatment does not cure the viral infection but can reduce the signs of illness. Acyclovir or related anti-herpes compounds can be used. For birds with clincal signs, Acyclovir is given by IV or subcutaneous injection. For exposed birds, anti-herpes compounds are given orally through a feeding tube. For flocks, medication can be added to the food or water.
In some cases, supportive care such as fluids and force-feedings may be needed.
Home Care and Prevention
Any bird undergoing treatment for Pacheco's disease must be kept in isolation. Birds exposed to ill birds should also be quarantined.
Thoroughly clean and disinfect enclosures, food bowls and non-porous toys and perches. Discard porous (wood, natural fibers, rope) objects that cannot be thoroughly cleaned and disinfected and do not replace them until treatment and vaccination is completed.
On a daily basis, monitor fecal output to ensure proper food consumption and digestion of any ill bird. Monitor and record daily weight to detect changes.
Pacheco's disease is much easier to prevent than to treat. Preventative measures include:
- Reducing crowding and improve air circulation and hygiene.
- Keep your bird out of direct or indirect contact with other birds.
- Enjoy the bird you have. If you decide to add a new bird, he should be quarantined for at least 90 days and be examined by an avian veterinarian at the beginning and end of quarantine.
- Have any new bird tested using an antibody assay and/or vaccinated during quarantine.
- Quarantine any bird that has been taken from the home or aviary and exposed to other birds before placing him back in the home or aviary.
- Use biosecure-shipping containers to prevent exposure to PDV during transport.
- Once an outbreak has occurred, maintain a routine vaccination schedule as recommended by your avian veterinarian.
- An inactivated vaccine can be used to prevent the severe disease associated with some natural infections.
Pacheco's disease (PDV) has been reported in psittacine birds from North and South America, Africa, Europe, Australia and Asia. The clinical and microscopic changes that are called Pacheco's disease can be caused by any one of at least three distinct psittacine herpesviruses. It is probable that many other psittacine herpesviruses will be identified.
Most species of free-ranging and domestic birds are considered susceptible to some strain of herpesvirus, but thus far PDV has only been shown to cause disease in psittacine birds following natural exposure. This is typical for herpesviruses, which tend to be highly host specific. The herpesviruses that cause problems in humans are not known to infect psittacine birds and PDV is not known to infect humans.
Disease progression can vary widely depending on the virulence (aggressiveness) of the infecting strain of virus and the species and condition of the infected bird. In general, Old World psittacine birds (cockatoos, African grey parrots, lovebirds, budgerigars) are considered more resistant to severe forms of the disease than New World psittacines (macaws, Amazon parrots, conures). However, susceptibility does vary widely among individual species within a group.
The fact that many healthy psittacine birds have antibodies against PDV suggests that some infected birds mount an appropriate immune response that prevents the virus from causing progressive disease. It is safest to assume that survivors are infected for life and can intermittently shed the virus. This type of persistent infection is called latency.
Some infected birds die without showing any signs of disease while others die shortly after clinical changes are first noted. Clinical signs may include depression, anorexia, diarrhea (which may or may not contain blood), regurgitation and yellow-green urates suggestive of liver damage. In the final stages of the disease, birds frequently show signs of nervous system damage including difficulty standing or moving, body tremors or seizures. Most psittacine birds die within several hours to two days of showing clinical signs. Birds infected with less aggressive strains of the virus are more likely to survive than those infected with virulent strains, particularly if clinical signs of disease occur. The clinical changes associated with Pacheco's disease may also be caused by bacterial liver disease, chlamydiosis, salmonellosis, liver toxins, avian polyomavirus, reovirus and adenovirus.
- Birds exposed to virulent strains of PDV usually develop clinical signs or die within 3 to 14 days after being exposed to the virus.
- Virus spread depends on many factors – the hygiene in the aviary, the species of exposed birds, the distance between enclosures, the strain of the virus and the condition of the flock. Most birds are infected with PDV after they ingest contaminated excrement. Thus, aviary hygiene is critical in preventing PDV outbreaks.
- PDV is most frequently transmitted through direct contact with feces, or respiratory secretions from an actively infected bird. Crowding, poor air circulation, accumulation of excrement and stacking of enclosures increase the likelihood of PDV transmission from infected to susceptible birds. This organism is not considered stable when outside the host and is probably inactivated without hours to days in most conditions. Cool, moist conditions and freezing will preserve the infectivity of most viruses.
- Pacheco's disease outbreaks usually occur when a new bird has been added to an established group or when stressful events (such as breeding, unseasonable climatic conditions, malnutrition, storms, fires, rodent infestations, etc.) cause a latently infected bird to begin shedding. Exposing unvaccinated birds to situations where they might have encountered birds that were shedding the virus (such as bird fairs or sexing clinics) can also cause an outbreak.
Pacheco's disease should be considered in any bird that dies suddenly with no signs of illness, particularly if some stressful event has occurred in the past three days to two weeks. Pacheco's disease should also be considered in birds that die shortly after developing clinical signs that include depression, anorexia, diarrhea (which may or may not contain blood), regurgitation and yellow-green urates.
Most cases of Pacheco's disease are suspected when viral factories called inclusion bodies are seen in the cells of the liver using a microscope. The disease is definitively diagnosed using viral specific DNA probes are by culturing the virus from infected tissues.
- Your veterinarian may use radiographs (X-rays) or changes in the types of blood cells (CBC) or enzymes found in the blood (blood chemistry) to evaluate the overall health status of a sick bird.
- The most common radiographic change associated with PDV is an enlarged liver. However, this radiographic change can also occur from other causes.
- The most common changes in the blood are a substantial increase in liver enzyme activity and a decrease in the number of white blood cells. These blood changes can also occur from other causes, which is why specialized testing of swabs of the choana and feces and/or serum will be necessary to determine if an active PDV infection is occurring.
- Until the site of viral persistence has been documented, use of an antibody detection assay is likely to remain the best test for screening clinically normal birds to determine if they have previously been infected or vaccinated. A virus neutralization assay is the most commonly used antibody test. Because PDV causes a lifelong infection, demonstrating that an unvaccinated bird has an antibody titer suggests that the bird has survived an infection and the bird should be considered latently infected. If detecting antibodies in an unvaccinated bird will be used to make life changing decisions for the bird, then it is important to repeat the test to make certain that some laboratory error did not occur.
- Confirming an active case of PDV is best achieved by combining tests that detect antibodies against the organism with tests that demonstrate that PDV is present in a sample. Tests to detect the presence of the virus include culture and DNA probe-based assays (PCR). These tests are most valuable in birds with suggestive clinical signs, since they are most likely to be shedding PDV from the respiratory and/or gastrointestinal tract. Culture remains the gold standard for documenting the presence of PDV in a clinical sample. However, culture is problematic, time-consuming and expensive in comparison to other tests. If a swab for DNA probe-based testing or culture is not slimy after sampling the choana and not coated with excrement after sampling the feces, then the sample is of poor quality.
- Currently, there is no test that can be used to confirm that a bird does not have PDV.
Acyclovir has been shown to reduce the severity of herpesvirus infections and to decrease the number of deaths in an outbreak. This drug and related compounds would be expected to be most effective when treatment is started before a bird develops clinical signs of disease. This drug has been linked to kidney damage in some species and should only be used when necessary and under the supervision of an avian veterinarian.
In birds with active signs of disease, your veterinarian may choose to administer acyclovir by either an intravenous or subcutaneous route. If you have birds that have been exposed but that are clinically normal, your veterinarian is likely to give acyclovir through a crop tube. If a flock is being treated, your veterinarian will instruct you on how to add acyclovir to the food and/or water.
Other therapies that may be needed include fluids to correct dehydration and supportive nutrition if the bird has not eaten for several days or has lost considerable weight.
Once acyclovir therapy has been initiated, it is important to start vaccinating. The acyclovir should help reduce the number of birds that will die while the vaccination program should help provide long-term protection of uninfected birds.
Optimal treatment for your companion bird requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your bird does not rapidly improve.
Make certain you administer all prescribed medications at the appropriate time intervals. Contact your veterinarian immediately if you are having difficulties treating your bird as prescribed. If you are having problems, it may be best to hospitalize your bird to assure that a proper course of treatment is administered.
Any bird suspected of having Pacheco's disease, that has been exposed to birds with PDV or that is being treated for PDV should be isolated from other birds to prevent transmission. The common practice of placing a hospital or "sick" room in the same building or airspace with a psittacine nursery is NOT recommended.
As with most viruses, organic debris such as blood, soil, nesting material or feces would be expected to protect PDV from disinfectants that do not contain detergents. Caretakers should always wear a dust mask when handling the waste of birds. To reduce dust, use a misting bottle filled with disinfectant to moisten excrement and feather debris before handling. PDV can be inactivated with household bleach and most common disinfectants.
Deaths should stop within two to three days after starting acyclovir therapy. If deaths continue, you should contact your veterinarian.