Avian spirochaetosis

Synonyms

Introduction

Avian spirochaetosis affects a number of avian species including chickens, turkeys, pheasants, ducks and geese as well as game birds. It is spread transovarially and trans-stadially, by softticks of the Argas (fowl ticks) family, but direct transmission via the faeco-oral route also occurs. The organism has been found to survive for up to two months in droppings, but is susceptable to disinfectants. Direct transmission of the disease can also occur through cannibalism, scavenging on infected carcasses or multiple use of needles and syringes by the stock men.
Outbreaks of the disease tend to occur during peak tick activity during warm, humid conditions.

There is no specificity of the disease for any age of chickens, with all being susceptable. Free-range or chickens living on litter bedding are more susceptable to the disease than battery hens. The disease is also less prevelent in broiler chickens due to the 'all in all out' system in these cases. Exotic breeds will sucumb to the disease more readily than native birds.

Clinical Signs

Birds will appear depressed, have cyanotic wattles and have signs of general malaise including anorexia, dehydration ruffled feathers, huddling and in-activity. Later, a fever will occur and there will be noticable weight loss.

Birds will have diarrhoea which may be green and greasy in appearance and there will be staining around the cloaca.

In the terminal stages of the disease, the birds will become anaemic and will develop paresis or paralysis.

If birds recover they will be emaciated and and have temporary paralysis and egg production will decrease massively.

Diagnosis

Clinical signs as well as history and signalment will aid the diagnosis.

A sick bird should be sacrificed and necropsy performed as the main diagnostic tool. Signs on post mortem will include marked enlargement and mottling of the spleen and liver. Kidneys may also be swollen and pale and haemorrhages may be seen in all other organs. Green, mucoid contents are likely to be found in the intestines.

Evidence of ticks or tick bites on the bird or presence of ticks in the poultry house increases the likelihood of spirochaetosis.

Definative diagnosis is by evidence of B.anserina in affected bird by dark-field microscopy or silver impregnation staining procedures from blood or tissues. B. anserina can also be isolated by inoculation of embryonated eggs or chicks as it cannot be cultured on normal bacteriological media.

Treatment and Control

Antibiotics including penicillin, streptomnycin, chloramphenicol, tylosin and tetracyclines are effective in treatment of the disease.

Inactivated vaccines are avaliable and will provide immunity, however the easiest and most common control method is the prevention of fowl tick infestation through the use of ectoparasiticides.

References

Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial
Jordan, F, Pattison, M, Alexander, D, Faragher, T, (1999) Poultry Diesease (Fifth edition) W.B. Saunders
Randell, C.J, (1985) Disease of the Domestic Fowl and Turkey, Wolfe Medical Publication Ltd
Saif, Y.M, (2008) Disease of Poultry (Twelfth edition) Blackwell Publishing