Susan L. Clubb, DVM
Kenneth H. Eskelund, DVM*
Pet Farm Inc.
5400 NW 84 Ave
Miami, Florida 33166 :
*Maine Biological Laboratories
P. 0. Box 255
Waterville, Maine 04901
Any avian veterinarian who has dealt with psittacine pox virus infection in young Blue- fronted Amazons (Amazona aestiva) can attest to the devastating effects of this virus. Parrot pox is most common in Amazons and pionus, so much so, as to limit the ability of importers to successsfully supply these species to the public. Blue-fronted Amazons are particularly susceptible and most often infected. Many other species are susceptible and become infected when exposed to infected birds, mosquitoes or contaminated fomites. While pox is uncommon in captive collections, the virus can be introduced by infected birds or mosquitos which may come from neighboring collections.
The clinical signs, course of the disease, treatment, etc. have been described previously as well as attempts to control the disease using a variety of live virus vac-cines.1,4,8,9 Parrotpox virus appears to be antigenically distinct from fowlpox, pigeonpox and quailpox viruses.2 Research with parrotpox virus in chickens indicates that it will produce skin lesions in one-day-old and ten-day-old SPF (specific pathogen free) chicks.2 Fowlpox and pigeonpox vaccination did not protect chicks from parrotpox challenge.2 Similarly, parrotpox-vaccinated chicks were not protected against fowlpox challenge.2 Likewise, the use of available vaccines for fowlpox or pigeonpox has been unsuccessful when used in the field in work with Amazons.5 Gerlach described three distinct pox viruses in psittacine birds, Agapornispox (lovebird pox) psittacinepox (Amazon pox) and budgerigarpox and indicated that antigenic relationships of these viruses were unknown.7
Avian pox virus isolates frequently infect heterologous hosts and may be used in these hosts as vaccines, but are usually most pathogenic in the species from which they were isolated. For example, pigeonpox viruses are used to protect chickens from fowlpox but the immunity is not as long lasting as the more risky vaccination of chickens with fowlpox virus vaccines. The use of live homologous virus vaccines of psittacine origin have been promising in some heterologous psittacine species, but they have proven too virulent for use in Blue-fronted Amazons, the primary target species and species from which an experimental virus was isolated from a mild natural outbreak.4,9 In laboratory and field studies, this avirulent field isolate of parrotpox virus was used as a vaccine for laboratory trials using Peach-faced Lovebirds (Agapomis roseicollis) and field trials using Blue- fronted Amazons and Red-lored Amazons (Amazona autumnalis).4,9 This virus proved to be successful as a vaccine for the lovebirds and Red-lored Amazons but was too virulent for use in Blue- fronted Amazons.4,9
Recognizing that wide spectrum of psittacine species which would benefit from vaccination and the relative risk of using live virus vaccines, especially in large groups of birds under stressful conditions such as those encountered in importation, experiments were initiated utilizing killed virus vaccines.
THE VACCINE
The experimental parrotpox killed virus vaccine (PPKV) was produced by Maine Biological Laboratories. The vaccine virus was obtained from Dr. Willie Reed of Purdue University, West Lafayette, Indiana. The virus was first isolated by Drs. Boosinger and Winter-field at Purdue University from Amazons dying with severe diphtheritic pox lesions.2 The isolate has the ability to infect Amazon parrots, lovebirds an a variety of other psittacine species.
The vaccine was an aqueous in oil emulsion. The aqueous portion consisted of infected CAMS (chorioallantoic membranes) from SPF eggs mixed 1:1 with sterile saline and ground in a mini-waring blender and inactivated with 0.3% BPL (Beta Propriolactone).
FIELD TRIAL #1
On 4-19-87, 650 adult Blue-fronted Amazons were imported from Argentina. Twenty six (26) birds died during quarantine and upon release from quarantine, lesions of pox were noted in a few birds. On 5-5-87, 100 birds were vaccinated with a single intramuscular dose of 0.5 ml killed pox vaccine. No signs of adverse reaction were noted at the time of vaccination. Vaccinates and non- vaccinates were housed in the same room under identical conditions. Records on mortality and morbidity (development of characteristic lesions) were maintained for the following 43 days. The results of examination of all birds on 6-9-87 is summarized in Figure #1.
This flock had a concurrent problem with sinusitis and pneumonia (etiology unknown but may have been associated with mycoplasma) which could have accounted for some of the mortality. This virus was typical of the strains encountered frequently in Blue-fronted Amazons, strains which cause severe diphtheritic lesions of the oral and ocular mucosa. It was also observed that pox lesions were less severe in the vaccinates and that they healed more rapidly.
FIELD TRIAL # 2
A trial was conducted using vaccinated Blue-fronted Amazons and unvaccinated Peach-faced Lovebirds as controls. The Blue-fronts were young, recently weaned birds from a flock in which no pox had been found. The Peach-faced were young, captive bom on a farm with no known pox exposure. Following release from quarantine, 5 Blue-fronted Amazons were vaccinated with 1 dose, 0.05 mg, PPKV by intramuscular injection in the breast muscle. They were revaccinated 4 weeks later. Five (5) Peach-faced Lovebirds were maintained as controls. Four (4) weeks following the second vacination, vaccinates and controls were challenged by a single needle wing-web stab with a virus (CAM 2080-78 PS) with a titer of 5.8 log 10 EID 50 per ml as described by Winterfield et al.9 All birds were observed for 43 days post-challenge and pox lesions and severity were recorded and summarized in Figure #2.
In this trial all vaccinates developed lesions at the site of inoculation as well as systemic lesions. In comparison to the controls, however, the lesions observed in the vaccinates developed later and the birds recovered sooner. It must be noted that the Blue-fronts are much more susceptible to disease with the challenge virus than the Peach-face, therefore the Peach-face are not good controls for a challenge trial using Blue-fronts.
FIELD TRIAL # 3
Fourteen Peach-faced Lovebirds, young, captive bom birds with no known exposure to pox, were vaccinated with .25 ml PPKV by intramuscular injection in the breast muscle. Five (5) additional birds were maintained as controls. All vaccinated were revaccinated 4 weeks following the initial vaccination.
The 5 control birds and 7 of the vaccinates were challenged 5 1/2 weeks after revaccin-ation (9 1/2 weeks after the initial vaccination). Birds were challenged as described in Trial #2. The other 7 vaccinated birds were maintained in the same cage as a contact-challenge. Each bird was examinedb on days 7, 10, 13, 17, 21, 25 and 38 post-challenge and all lesions of pox were recorded. Results of the trial are summarized in Figure #3.
Two vaccinates, one wing web challenge and one contact challenge, died during the experiment due to bacterial enteritis. Both of these birds had no signs or lesions of -pox and their deaths appeared to be unrelated to the challenge. All of the challenge controls showed swelling at the site of inoculation on day 7 and oral or ophthalmic pox lesions on day 10. By 35 days PI 3 of 5 (60%) controls had died. In the vaccinated challenge group one bird had pox lesions at day 7 and another at 17 days. Both birds died. However, none of the vaccinates that were challenged by contact showed any pox lesions.
This trial indicated that vaccination gave partial protection to vaccinated lovebirds against direct challenge with a virulent virus, and complete protection to contact challenge.
FIELD TRIAL # 4
On 2-14-88 850 handfeeding Blue-fronted Amazons were imported from Argentina. Twenty-nine (29) birds died during quarantine. One week after release from quarantine, a portion of these birds were vaccinated for parrot pox. At that time 8 of the 813 remaining birds were showing lesions of parrotpox, and 8 had died during the week between release and vaccination.
On 3-24-88, 212 birds in 20 cages were vaccinated with a single dose (OS ml) of PPKV. All vaccinated birds were marked with a subcutaneous injection of india ink in order to ensure accurate identification of vaccinates. In addition all band numbers, and cage numbers were recorded along with any lesions. Daily records of mortality were maintained with individual identification of each vaccinate. 202 non-vaccinated birds were maintained in the same room in identical caging. No placebo injections were given and individual records were not kept on non-vaccinates. The remaining 399 birds were not included in the study and were moved to another premise.
On 4-25-88 total mortality was recorded and each living bird was re-examined and lesions noted. Results are summarized in Figure # 4. Mortality was minimal after 4-25.
The strain of parrotpox virus encountered in this flock was a strain which had an affinity for the trachea. A large percentage (probably 90% or more) of the mortality was due to asphyxiation by lesions on the glottis or in the trachea.
The data shows a decrease in overall mortality as well as a^decrease in the severity of disease in affected birds. It must be considered that the infection was well established in the flock at the time of infection, however vaccination in the face of this outbreak resulted in a reduction in mortality and a reduction in the severity of lesions.
FIELD TRIAL # 5
Six Hundred (600) Blue-fronted Amazons and 200 Tucuman Amazons (Amazona tucumana) were imported from Argentina on 5-14-88. With permission of USDA- APHIS, 420 Blue-fronts and 133 Tucuman Amazons were vaccinated on 5-20-88 with a single dose, 0.5 ml of PPKV by intramuscular injection into the breast muscle. The balance of the birds were maintained in the same room as unvaccinated controls. Vaccinated birds were banded on the left leg and non-vaccinated birds were banded on the right leg. After vaccination all birds were observed for any adverse reactions. While in the quarantine station and upon release from quarantine, all birds were examined for any evidence of pox infection.
There was no evidence of any adverse reaction to the vaccine. The birds were released from quarantine on 6-13-88. During quarantine there was no evidence of psittacine pox in any of the vaccinated or unvaccinated birds. Only 3 birds died during quarantine from causes unrelated to either vaccination or parrot pox infection. Conjunctivitis was observed in 17 Tucuman Amazons but upon conjunctiva! biopsy of 8 of these birds, no pox virus was found, and the birds had no other signs or lesions of pox virus infection. The conjunctivitis appears to have been caused by a protozoal infection and was unrelated to pox virus infection.
The flock remained stable through mid-August (time of writing) with no signs of adverse vaccine reaction or pox virus infection (12 weeks post-vaccination) . Vaccine efficacy could not be shown in this trial because psittacine pox infection did not occur naturally and challenge was not elected. However, vaccine safety was demonstrated, as this group had unusually low morbidity of only 0.54% (3 of 555) during the quarantine period and continued .
SUGGESTED USE
Susceptible species intended for importation should ideally be vaccinated as soon as possible after capture, in the country of origin, prior to exportation. Birds should be vaccinated (or revaccinated) as soon as possible after arrival at the quarantine station. An ideal time is in conjunction with banding, as all birds must be handled at this time. A second or third dose should be given upon release from quarantine to enhance the immune response at a time when the bird may be exposed to many other birds.
Birds entering pet shops are at risk of pox virus infection if exposed to diseased birds or contaminated equipment. All susceptible species should be vaccinated during the initial quarantine holding period before exposure to existing shop livestock. A second vaccination should be given 4 to 8 weeks after the first. In a situation where turnover is rapid, the booster may be administered at 2 to 4 weeks. A single booster should be given annually as long as the birds are at risk.
In breeding collections where psittacine pox virus has been diagnosed, all susceptible breeders should be vaccinated with 2 doses, 4 to 8 weeks apart in the non-breeding season (fall) or at the first sign of an outbreak. A single booster vaccination should be given annually. Chicks should be vaccinated 1 to 3 weeks prior to fledging and a booster given 4 to 8 weeks later (the booster may be given in two weeks if necessary for marketing).
Vaccination in the face of an outbreak carries with it the inherent danger of spread of disease. If early in an outbreak, vaccination may reduce morbidity or mortality. In such a situation, care must be taken to use sterile needles for each bird and to wash hands or use disinfected handling materials between birds. In advance outbreaks vaccination may be contraindicated. Vaccination of healthy birds, in advance of potential exposure, is recommended.
DISCUSSION
Historically, live viruses have been used almost exclusively for vaccination against poxvirus infections in a variety of species, mammalian and avian. The combined factors of a large number of susceptible species, use in a stressful and densely populated environment such as encountered in trade channels and quarantine, and the expense of testing to prove safety for a variety of species, made the use of live virus vaccines impractical for psittacine pox. Initial trials indicated that killed parrot pox vaccines are safe and show some degree of efficacy, even in the face of a natural outbreak. There may be differences in effectiveness depending on: the length of time between vaccination and exposure, the number or doses given, virulence and organ specificity of the virus, route of exposure, species, age, other complicating diseases, and other unknown factors.
While protection from a killed vaccine may not be as long lasting or as complete as that which would be afforded by vaccination with live viruses, the safety of a killed virus vaccine is a fair tradeoff.
A dream, or prediction, for an ideal pox control program for the future may include vaccination of birds at the time of capture with a killed virus vaccine, with boosters given once or twice at appropriate intervals while birds are in trade channels. After the birds have sufficient immunity from the killed vaccines, follow-up vaccination with a live virus vaccine would provide durable, solid immunity. Some of the tools for such a program are already in place. A recent regulatory change will now allow use of licensed vaccines in imported birds during quarantine.
Parrot pox, in the author's opinion, is the most consistent and devastating viral disease encountered in imported Blue-fronted Amazon parrots and many other species. Blue-fronts are especially desirable in the pet trade as they are readily available as young tame birds, are beautiful, have excellent pet potential and are economically priced, but at this time they do not breed freely in captivity. This places a pressure on wild populations. Blue-fronts are classified by CITES (Convention on Trade in Endangered Species of Wild Fauna and Flora) as a species which can sustain the pressures of trade, but mortality is high in trade due to disease and primarily due to pox. As restrictions on the importation of birds increase and fewer species are available, it becomes more important than ever to take every possible step to protect these birds from catastrophic disease outbreaks. As other species have become unavailable, the numbers of Blue-fronts imported into the U.S. from Argentina has risen annually from 2,559 in 1981, 9,652 in 1982, 16,946 in 1983, 10,406 in 1984, to 25,554 in 1985 (Figures from TRAFFIC USA). Although Blue-fronts are considered a pest species in Argentina and are freely exported, unlimited harvesting can, with time, reduce wild populations. '''Management of captive populations also depends on effective disease control methods. This will, in turn, reduce pressures placed on wild populations.
Vaccination for pox would also benefit other psittacine species such as Amazons and pio-nus from South and Central America, macaws, Quaker parakeets, conures and parakeets from South America, lovebirds from Africa, and possibly lorys from Indonesia. Future regulations may even REQUIRE vaccination prior to importation.
REFERENCES
1. McDonald, S.E., Lowenstein, LJ., and Ardans, A.A.: Avian pox in blue-fronted Amazon parrots, JAVMA 179:1218-1222, 1981.
2. Boosinger, T.R., Winterfield, R.W., Feldman, D.S., and Dhillon, A.S.; Psittacine pox virus: virus isolation and identification, transmission, and cross-challenge studies in parrots and chickens. Avian Dis 26:437-444, 1972.
3. Clubb, S.L.; Avian pox in cage and aviary birds. In Zoo and Wild Animal Medicine, 2nd Edition; M. Fowler editor, pp. 213-220, 1986.
4. Clubb, S.L., Winterfield, R.W., and Cramm, D.; Laboratory and field trials with a parrot pox vaccine. Proceedings of AAV, pp. 71-82, 1985.
5. Clubb, S.L. - Unpublished data.
6. Federal Register/ Vol. 53 No. 134/ Wednesday, July 13, 1988. (9 CFR part 92) Vaccination of birds in quarantine.
7. Gerlach, H. Viral diseases: In Clinical Avian Medicine and Surgery, GJ Hamson and LR Harrison (eds), pp: 408-433, 1986.
8. Winterfield, R.W., and Reed, W.; Avian pox: infection and immunity with quail, psittacine, fowl and pigeon pox viruses. Poult Sci 64:65-70, 1985.
9. Winterfield, R.W., Clubb, S.L., and Schrader, D.: Immunization against psittacine pox. Avian Dis 29:886-890, 1986.