Giardia in Birds | Asymptomatic carriers may exist, and serve as sources of infection for other birds.
Giardia from Protozoan parasites of cage and aviary birds, 2001, Avery
1 - Epidemiology and Pathogenesis
Giardia is a simple binucleate flagellate with a large ventral sucking disc. It has a simple life cycle involving longitudinal binary fission in the small intestine , migration to the large intestine and formation of cysts that are shed in the faeces (Petrak 1969). Gastro-intestinal signs are due to massive attachment to the villi of the proximal gut by sucking discs of the parasites causing a competitive malabsorptive state involving fats, vitamins and proteins (Clyde and Patton 1996, Clipsham 1995). It is found predominantly in psittacines, but rarely in amazons, conures, cockatoos or macaws (Fudge 1985). Transmission is via faecal-oral route. Giardia species found in mammals are not pathogenic to avian species (Doneley 1996).
Immunity to infection is short lived only (Gallagher, Gartrell and Upcroft 1995). Infected animals are commonly nutritionally marginal, overcrowded or unhygenically kept (Doneley 1996). Outbreaks commonly follow introductions and stressors such as molting, incubation, and poor ventilation (Greve 1996).
2 - Diagnosis
Giardiasis has a number of sydromes associated with it. The major syndrome is one of chronic, recurrent diarrhoea that is mucoid, discolored and foul smelling combined with weight loss, vomiting, lethargy and anorexia (Petrak 1969, Clipsham 1995). Another syndrome that may be seen independently or in combination with gastrointestinal signs is one of excessive feather grooming, oily greasy feathers, feather picking and screaming, whole seeds in droppings, dry skin, pruritus, and bleeding feather quills. This latter syndrome is the result of malabsorption of fat soluble vitamins, riboflavin, essential fats, and proteins and it is suggested that also an allergic reaction to Giardia may be involved (Cannon 1996, Fudge 1985). A third syndrome of shifting leg lameness and rough feathering is associated with white muscle disease due to inability to absorb vitamin E (Clipsham 1995).
Microscopic evaluation of infection requires a refined technique to avoid false negatives. A single negative sample is not considered as diagnostic. A lightly concentrated, fresh smear taken from faeces less than ten minutes old should be examined under at least 20 high dry fields within three minutes of making the smear.
Protozoan Parasites of Cage and Aviary Birds
Giardial cysts are often confused with yeasts or urate crystals and are often overlooked. Giardia trophozoites have a characteristic gliding, “falling leaf” motion (see Appendix II) and two nucleii “eye spots” (Clyde and Patton 1996, Clipsham 1995). The trophozoites are delicate organisms and if the substage diaphragm is nearly closed this will maximise contrast (Greve 1996). Standard sugar/salt flotation will distort cysts and destroy trophozoites. Cyst concentration and visualisation may be improved by Zinc Sulphate flotation or by gauze straining the sample and
centrifuging the liquid at 1200 rpm for 10 minutes. The use of faecal ELISA is controversial and it is suggested that three zinc flotations will give better results (Clipsham 1995). Faecal trichrome staining of sample collected into polyvinyl alcohol or 5% formalin can be used to highlight trophozoites. Trophozoites will appear bluegreen, nuclear material, erythrocytes and bacteria appear purple/ red and eggs and larvae red (Fudge 1985).
Airdried faecal smears can be stained by flooding with carbol fuschin (from an acid fast kit) for 60 seconds, then rinse and air dry. The trophozoites and cysts will stain deep red (Dalhausen 1993). Post mortem of infected adults shows the small intestine typically dilated and filled with a milky broth-like contents but normal mucosa.Infected chicks will have a distended crop as well (Greve 1996). A circulating eosinophilia or hyperproteinaemia may be seen but are not consistent (Greve1996).
Treatment and Control
Therapeutic treatment alone is insufficient to control Giardiasis. Therapies include metronidazole (orally, in water or injectable), carnidazole, fenbendazole (50 mg/kg x 3 days), albendazole (10 mg/kg x 5 days). The nitroimidazoles maycause secondary Candidiasis bykilling off competitive anaerobic gut flora (Clipsham 1995, Fudge 1985). Metronidazole will relieve pruritus within hours of administration . Improved nutrition, reduced stress, vitamin A, vitamin D3, vitamin B5 and vitamin E can all be utilised during treatment.(Fudge 1985).
Relapses can be due to incomplete treatments, resistance, or environmental reservoirs. Sanitation is an important adjunct to treatment and limiting faecal access and the use of quaternary ammonia disinfectants to inactivatecysts is essential (Doneley 1996, Clyde and Patton 1996).rdia.