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
The herpesviruses that cause Pacheco's disease are not known to infect humans or to infect other types of birds naturally.
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:
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.
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.
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.