An Outbreak of Herpes Virus and its Future Prevention in an Indoor Parrot Breeding Facility

10 min read
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By Mark Hagen, M.Ag.
Director of Research


  • Introduction
  • The Facility
  • History and Treatment
  • Mortality
  • Serology
  • Recovery
  • Vaccination
  • Stress and Disease
  • Summary
  • Bibliography


Pacheco’s disease is a highly fatal, contagious disease of psittacine birds. It is caused by a psittacine herpes virus. The spread through a susceptible population is rapid and most psittacine species are susceptible to the disease. The Hagen Avicultural Research Institute (HARI) unfortunately experienced an outbreak of this disease in January/February of 1989. Similar outbreaks have occurred in large parrot holding facilities in the past. This outbreak at HARI and means to prevent such outbreaks will be reviewed.


At HARI the birds are housed indoors all year, similarly to many northern breeders. We operate with three months “winter” i.e. misters off, eight hours of light and cooler temperatures followed by six months of “summer” i.e. misting, 14 hours of light and warmer temperatures. When our overhead green house misters are on, the air is saturated with tiny water droplets. Our pairs go into a bathing frenzy under the misters especially at the start of the breeding season.

The leased building that HARI occupied at the time of the outbreak was not specially designed as an animal holding facility. Our winter heating costs are high due to our cold winters. A reduced amount of interior air was exchanged with the cold fresh outside air; we had turned off our venting barn fan. Our veterinarian commented that the air was of questionable quality and that we should get an engineer to design a good ventilation system. There is usually little dust in the air nor does it smell. The circulation pattern of air was determined by the heater fans and is not based on minimizing transfer between pairs. However since we were moving out of this building shortly it was decided not to invest in an expensive ventilation system for this temporary facility.


Then under simulated “summer” conditions HARI experienced a terrible herpes virus outbreak in January and February 1989. We felt strongly that the virus was spread via the water droplets in the air contaminated from the feces soiled cage wire and floor waste. We’re not sure of the source; if it was a long term carrier bird that has been at HARI for years or a bird which was introduced in the fall when 18 new birds were added to the colony. The latest acquisitions were from our own quarantines, in which no problems had occurred, or were previous pets. These birds included four astral conures, four black-headed caiques, four white-capped pionus, four moluccan cockatoos and two double-yellow headed amazons. For various reasons I do not think one of these birds brought in the virus but that it was being shed by one of our established birds. Based on previous experiences I believe we may have yellow-naped and/or yellow-winged amazon carriers who are intermittent shedders of some host adapted virus.

Our amazons are set up in one long row of 76 cm wide x 152 cm high x 320 cm long split cages with very little space, about 10 cm between each set of two cages. The species are in random order. Sudden mortality began in the area where the air flow from the propane heater was greatest, near the middle of this row. Over a one week period the disease spread down to each end of the row, thus it is assumed that all the birds down this row were exposed to the virus. Most of the birds that died did so within two days of becoming clinically ill. At this point it was decided to move all the surviving sick birds to another location for isolation and supportive care.

Supplemental tube feeding was required for 5 to 10 days in sick birds most of which stop eating. The food used was a high performance formula, 24% protein and 9% fat (Tropican – Hagen) which is also used for handfeeding babies and as a breeding pellet. Acyclovir (Zovirax – Wellcome) a drug to treat human genital herpes was administered both orally via the tube fed food and as an injectable (intramuscular). Zovirax is very expensive and its effectiveness in sick parrots is still undocumented. Most of the birds that survived the first three days would go on to recover making all the supplemental care and medical treatments worthwhile. If we were to do truly scientific research half the sick birds should not have received the acyclovir. This would allow a comparison with a control group to observe differences in mortality. However, these birds are not only valuable but also companion animals, each with its unique behaviours. Every effort was made to save each one.


Twenty seven per cent of HARI’s amazons died (15 out of 56) with 13 sick birds surviving. Major species differences in susceptibility were observed; the double yellow-heads – 6 of 17 died plus most of the rest were sick, tucuman – 5 of 8 died, salvin’s – 2 of 3 died, and yellow-cheeked – 2 of 8 died, experienced the highest mortality and morbidity while our 10 yellow-naped, 6 yellow-fronted and 4 yellow-winged were resistant with no deaths and only 3 sick birds. All our yellow-naped amazons have come from quarantines where significant (about 25 %) acute mortality had occurred, but to which the federal lab in Ottawa could not identify the causative agent, although we believed that disease outbreak was caused by an amazon pox virus. Our macaws (21 pairs), and all of the old world birds (40 pairs of cockatoos, 8 pairs of african greys) were not affected. Only two moluccan cockatoos died and two others developed head tremors after being quite ill but recovering with tube-feeding and supportive care.

Two months later one military macaw and one moluccan cockatoo died suddenly on the same day. This occurred five days after a heater fan, that was implicated as the spreader of the causative agent during the major outbreak, was mistakenly turned on (the individual who turned it on no longer works at HARI!). The gross necropsy and histopathology of these two birds were very similar to many of the birds that died a few months earlier; swollen and congested liver, spleen, and intestines, some hepatocytes have the suggestion of viral inclusions. Frustratingly, again no virus was isolated by modified allantoic SPF egg inoculation.


Serological blood tests were performed on 9 of the birds that were sick and survived and on 5 that were not sick but were exposed to the virus and could be carriers. Potential carriers were identified based on their previous history which includes being previously associated with an outbreak in a quarantine station.

Serology confirmed the presence of Pacheco’s herpes virus anti-bodies in all birds that were sick and recovered. One of the birds, a yellow-naped amazon, which showed no signs of illness during the outbreak was positive for Pacheco anti-bodies.


The birds that recovered did so very quickly. One pair of double yellow-headed amazons were breeding and produced fertile eggs less than one month after being so sick they had to be force fed for 3 days. Marek’s disease in poultry is also caused by a herpes virus and egg transmission has not been demonstrated. We decided to pull the eggs, wipe them with a phenolic disinfectant and artificially incubating the eggs for hand-rearing. Two of the three fertile eggs hatched and were successfully raised.


A Pacheco’s Herpes vaccine produced from killed virus has been developed by Maine Biological Labs and is now available through some specialized and experienced Avian Veterinarians. Vaccination during an outbreak may spread the disease and will not save birds in the acute stage of the disease. Vaccination of all healthy birds within even closed breeding collections should be performed in advance of exposure.

There seems to be more evidence that different strains of herpes exist. Virology by the Veterinary Laboratory Services Branch (VLS) of the Ontario Ministry of Agriculture and Food (OMAF) did isolate Pacheco’s Herpes Virus, by egg inoculation, from some of the birds that have died in previous years at HARI. These were isolated losses with never a cage to cage spread.

But in this outbreak no virus was isolated although histopathology found hepatic intranuclear inclusions in most of the dead birds, which are suggestive of herpes virus which was confirmed by serology. The vaccine may only be good for the Pacheco’s strains of herpes and may not prevent an outbreak of other herpes viruses.


Vaccination itself stresses the birds since they must be handled and injected but it is still to be recommended. Health management includes a high quality balanced diet, caging which reduces stress and proper quarantine of new birds. Mate selection and pair bonding should be carefully monitored to produce compatible pairs and not lead to aggressiveness between birds.

When accompanied by sudden changes in temperature, or by moving, crowding, unusual noises, changes in the feed programme, or other management changes, the birds resistance is weakened. Multiple stresses cause a greater reaction than their sum would indicate. Many birds are carriers of disease organisms, but show no clinical signs. Stresses may trigger such an inactive state to an active disease.

There should be daily inspection of all birds to observe feed and water consumption and the state of their well being.


Aviculturists should use as many of the resources available as possible to prevent and monitor disease. This includes post mortems, professional experienced veterinary care and effective use of vaccinations and drugs to prevent disease such as Pacheco’s Parrot Disease and Psittacosis. Every aviculturist should establish a disease control plan in the case of an outbreak. Such planning will assist in the prevention of an outbreak as it may point out deficient areas of management which require improvement. This outbreak has now made disease prevention a top priority for HARI. All collections of Psittacines which include amazons should be vaccinated against Pacheco’s Disease as carriers may be present.


CLUBB, S.L. (1984). Disease control in the aviary. A.F.A. Vet. Seminar Proceedings. pp 72-81.

GASKIN, J.M., ROBBINS, C.M. and JACOBSON, E.R. (1978). An explosive outbreak of Pacheco’s parrot disease and preliminary experimental findings. Annual Proc. Amerc. Assoc. Zoo Vet. pp 241-253.

GASKIN, J.M., ARNOLD, D.A. and ROBBINS, C.M. (1980). An inactivated vaccine for psittacine herpesvirus infection (Pacheco’s disease). Amer. Ass. of Zoo Vet. Annual proceedings. pp 102-104.

GASKIN, J., RAPHAEL, B., MAJOR, A. and HALL, G. (1981). Pacheco’s Disease: The search for the elusive carrier bird. Amer. Assoc. of Zoo Vet. Annual proceedings. pp 24-28.

PANIGRAHY, B. and GRUMBLES, L.C. (1983). Pacheco;s disease in psittacine birds. Avian Diseases 28: 808-812.

GERLACH, H. and KITZING, D. (1982) Amazon – Tracheitis. 31st West. Poul. Dis. COnference + 16th Poul. Health Symp. pp 148-149.

KRAUTWALD, M.E., KALETA, E.F., FOERSTER, S., HERBST, W., SCHILGER, B. and SPENKOCH-PIPER, H. (1988) Heterogenicity of Pacheco’s disease and its causative agents. Ass. Avi. Vet. Ann. Meeting proc. pp 239-250.

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