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Editorial Information

John Dalton BVMS MRCVS

Diseases of Game Birds
Part 4 - Diseases from 10 days to 7 weeks of age


Disease incidence in gamebirds, 11 to 42 days old

fig1

Introduction. Many of the diseases seen in the first 10 to 12 days of life may also be encountered in the next growing phase of the game bird. If the main detail of one specific disease is in a previous bulletin it will be marked and so you should refer to that as well.

Aspergillosis

Cause. Infection of the respiratory tract with various fungi, mainly of the Aspergillus family (Fig 1). Damp shavings and straw are particular sources. Most commonly associated with poor air circulation in the brooder hut or night shelter. Partridge seem to be affected more often that pheasants, simply because of the amount of dust they create by their panic response to the slightest little movement within the house. Remember that the fungi are the agents of Farmer's Lung in humans.

Fig 1. Fungal hyphae from air sacculitis under microscope

Signs. Birds in this age group tend to present with severe respiratory signs. They are usually very unwilling to move and if they do may well fall over as a consequence. They stretch their necks to try to get easier passage of air into the lungs and air sacs. With secondary bacterial infection mortality rates may be high.

Post mortem. The lungs may well be fairly solid, but the most outstanding sign is the very great thickening of the walls of the air sacs. These may also have a creamy cheesy appearance. (Fig 2 & 3)

Fig 2.  Air sacculitis

Fig 3 Air sac with fungi clearly showing

Treatment. There is no specific treatment available for use. It may be dangerous to use anti-bacterial drugs as it may create an environment in which the fungi can super-proliferate. Iodine preparations have been used. The most important thing is to reduce the spread amongst the other birds. This can be done by regular cleaning and disinfection of the drinkers and feeders. Improving the ventilation is critical. Replacing contaminated litter is advisable, if possible. If not, it is possible to spray the spreading with anti-fungal agents, but this must be carried out with great care and may be of limited value.

Ascarid worms

Cause. Large roundworm, 50-80mm long. Mainly found in the upper intestines of partridges.

Signs. Large numbers will cause unthriftiness and may cause obstruction of the intestines resulting in death. (Fig 4)

Fig 4 Ascarid worms in Red Legged Partridge

Birds can be reared quite happily with a substantial burden, but we have seen significant mortality very soon after moving from the rearing field to release or holding pens.

Treatment. Flubenvet® is the licensed wormer for use in game birds. Other wormers are used, but have no licence for game birds.

Avian encephalomyelitis.

See description in previous bulletin 1 to 10 days old

Avian Influenza (See also in 0-10days bulletin)

Cause. Various influenza viruses. Can be transmitted to Man.

Signs. Variable, depends on Pathogenicity of the virus strain.

Treatment. None presently available for flocks of game birds

Control. Don't allow it in!


Capillaria(Hair worms)

More commonly seen once birds have been released, but if the rearing site is contaminated with eggs, may be seen with devastating effects, usually from August onwards.

Cause. Nematode worm, Capillaria contorta. Recent re-classification and some species are now referred to as Eucoleus. Are very thin and long (0.1 by 60mm). (Fig 5) (Very difficult to see with the naked eye.

Fig 5  Capillaria - whole worm

Signs. Poor growth and feathering. Mortality can be very high in young birds with heavy infestation in the crop. They burrow in the gut wall causing weakness, weight loss, difficulty swallowing, diarrhoea and death.

Fig 6 Capillaria - egg

Post mortem Diagnosis fairly straightforward, as the eggs have a characteristic "plug" at each end (Fig 6). It is often easier to identify the eggs than the intact worm because of its burrowing nature.

Treatment. Standard worming regimes may be sufficient, but sometimes a tougher approach has to be take with veterinary advice.

Coccidiosis (Cocci - pronounced "coxy")

Cause. An intra-cellular parasite of the intestinal tract of the genus Eimeria.

Fig 7 Coccidial oocysts

Fig 8 Caecal plug in Red Legged Partridge caused by coccidiosis

Signs. The disease is characterised by enteritis and diarrhoea, and is of great importance in the game bird and poultry industry. Even subclinical disease will still cause economic losses. Coccidia are host specific, meaning they only infect one species of bird and are site specific, meaning every species of coccidiosis colonises only a certain part of the intestinal tract Thus Pheasant cocci does not affect Partridge and vice-versa. Oocysts, tough hard shelled bodies (Fig 7) containing infective stages of cocci, are passed out in the droppings and ingested by other birds via contaminated drinking water and feed. Once ingested the coccidia go through a complex life cycle of several stages in the intestinal cells causing damage and disease. The life cycle can be as short as 7 days. Clinical signs include depression, reduced appetite, ruffled feathers, vent pecking, diarrhoea (sometimes containing blood), dehydration, weight loss and death. Red Leg Partridges are very susceptible and sudden deaths (in large numbers) are not uncommon. Grey partridges are seldom affected by coccidiosis.

Post mortem. Depending on the species of Eimeria involved there can be lesions seen in various parts of the intestine. Perhaps the most obvious is the caecal pug seen in caecal Coccidiosis in Red Legged Partridge (Fig 8). In pheasants intense inflammation of the intestine is more commonly seen. (Fig 9)

Fig 9 Coccidiosis: Damage (red spots) to the lining of the intestine (mucosa)

Prevention. The only product licensed in game birds is the coccidiostat Avatec®. This is usually included as a "standard" in all game feed for birds up to 13 weeks old.

Treatment. There are two major products used in the UK. Baycox® is licensed for use in poultry and so can be used on the prescribing "cascade". Amprolium is not licensed, but may be used under special licence if there are signs that the licensed product is not having the desired effect. These products may only be prescribed by a veterinary surgeon.

Control. Oocysts are very tough and can survive in the environment for a year. An ammonia based product (such as Oocide®) is needed to destroy them. It is almost impossible to prevent contact with oocysts. The best thing is to try and influence the balance between developing immunity and weight of challenge. Challenge can be reduced by the use of coccidiostats in feed, attention to hygiene (especially round drinkers and feeders) and avoiding re-use and overstocking of pens. The trick is to use a coccidiostat in feed at such a level that it allows birds to develop immunity before they are released, without them getting ill.

Fig 10. Gapes. Eggs from crop smear

Fig 11. Gapeworms in the trachea

Gapes

Cause. Syngamus trachea, commonly known as gapeworm, is the most important worm in game birds. More likely to be a problem with birds after release.

Life cycle. The adult worms live in the trachea (windpipe) of game birds, poultry and several other

birds such as rooks, crows and starlings, causing Gapes. The produced eggs are coughed up, swallowed and pass out in the droppings. An infective larva develops inside the egg. Birds may be infected by eating the eggs (Fig 10) or larvae, or by eating earthworms that have themselves eaten eggs or larvae. The larvae form a cyst in the muscle of the earthworm and may remain infective for up to 4.5 years, thus forming a reservoir of future infection. When swallowed by the bird the larvae migrate through the body or bloodstream to the trachea via the lungs. Here they rapidly grow into adult worms. The worms suck blood and can cause weight loss, anaemia, weakness and reduced egg production.

Signs. Respiratory signs, such as coughing and "snicking", are caused by irritation of the trachea by the worms. Head shaking after snicking is also a common sign. Death occurs by suffocation when worms block the airways. Partridges seem to be especially susceptible and mortality can be rapid and high.

Post mortem. The adult worms are easily seen in varying numbers in the trachea (windpipe) (Fig 11).

Treatment and Control. These two go hand in hand. It is virtually impossible to stop the birds being exposed to the worm egg, because of the wide variety of hosts. On the rearing field the risk can be reduced by ensuring wild birds have as little access as possible to the birds on the field.

Flubenvet® is the licensed wormer for use in game birds. Other wormers are used, but have no licence for game birds. Flubenvet® is incorporated in feed and is most commonly done for you at the mill. You do need a veterinary prescription (MFS) for this. This is another part of the Veterinary Health Plan you should draw up with your vet at the start of the season.

Hexamita/Spironucleus

Cause. Hexamita, now called Spironucleus, is a single cell organism, a protozoon, only slightly bigger than bacteria.

Signs. Acute disease characterised by enteritis with foamy/watery diarrhoea. Disease usually occurs in birds under 9 weeks of age. Symptoms include chilling, huddling, ruffled feathers, stilted gait (so called 'moon walking') and watery or foamy diarrhoea. Infected birds dehydrate rapidly and lose weight. They tend to throw food out of hoppers. Death occurs due to loss of electrolytes. Mortality may be as high as 75-90% in young birds!

Post mortem. Birds are emaciated and very dehydrated (Fig 12). The contents of the caecum (blind gut) are often yellow varying from pasty to very liquid consistency. Very high numbers of highly motile organisms can be readily identified in scrapings from the intestinal wall of affected birds. The organism may die soon after the death of the bird; therefore it is very important to present fresh birds, or even better, sick birds, to get an accurate diagnosis. Birds that survive will remain carriers and shed parasites with their faeces. The incidence of disease increases when successive hatches are placed in infected pens. It is also very simple to carry infection from pen to pen on dirty boots.

Fig 12. Hexamita. "Razor keel" caused by disease

Fig 13a. Hexamita. "typical" yellow frothy dropping

Diagnosis. Popular mythology is that you can diagnose this infestation by just looking at the droppings. Sadly other intestinal diseases also produce the same sort of yellow, frothy or custard like faeces (Fig 13a), which, in any case, are not consistently the case with Hexamita (13b).

Fig 13b. Hexamita - Opened caeca (blind gut) from one bird. Demonstrating that there is no "typical" colour to the content and thus the dropping.

Spread. Can spread between pheasants and partridges. It is often found together with other parasites such as Trichomonas and Coccidiosis. Transmission occurs via direct bird-to-bird contact and ingestion of droppings, contaminated feed or water. Cysts have fairly recently been identified in the mucus generated by the lining of the intestine.

Treatment. Since the banning of Emtryl® a few years ago, there is no licensed product available for this. Various antibiotics, together with electrolytes are frequently used with varying success. These are given both in liquid form and in feed. Again, if used in feed you do need a veterinary prescription (MFS) for this.

Necrotic enteritis and Ulcerative enteritis

(Examples of Clostridial bacterial infections)

Cause. Necrotic enteritis was first described in poultry in the 1960's and has subsequently been reported pretty much all over the world. It is defined as being related to infection with Clostridium perfringens (old name Clostridium welchii).

Signs. Most commonly the disease is seen in poultry being reared on litter. It is often associated with damage to the intestinal wall caused by other factors, such as coccidiosis. We have seen a similar gross pathology in Red Legged Partridges. Clostridium perfringens and several other clostridial species were isolated from affected birds. Coccidia were an incidental finding in some cases, but certainly not in all. The level of coccidial disease was regarded as being high enough to cause disease, but not the mortality rates seen in these cases. We have seen several episodes of ulcerative enteritis in Red Legged Partridge in the last few years.

Post mortem. Ulceration in the wall of the caecae is as a regular feature (Fig 14) Obvious signs of inflammatory change close to the junction of the small intestine with the blind gut (caecum). Ulcerative Enteritis has been described for over 100 years, and was initially seen in quail (hence its nickname Quail disease). It has also been seen in grouse, pigeons, chicken, and pheasants.

Fig 14. Ulcerative enteritis. Ulcers in the wall of the blind gut (caecum) in Red Legged Partridge.

Source. Clostridia are natural inhabitants of soil. They persist as spores. It is only when there is a trigger factor or factors, such as moving, hard weather, exposure to other intestinal injury (e.g. coccidiosis) that problems arise.

Treatment. In the first cases amoxycillin in water. Early bacteriology suggested that the organism found were resistant to this. Consequently it was changed to a fluoroquinolone, but the birds did seem to do better on the first choice treatment.

Pseudomonas.

Cause. Bacterial infection with Pseudomonas organism. Often a consequence of poor hatchery hygiene.

Signs. Can be seen in early rear or later. May be associated with high mortality. Sometimes presents as blindness with infection clearly visible inside the eye.

Treatment. Early diagnosis is vital, when antibiotics will help. Those with blindness are unlikely to show a very good response, but mortality can be reduced in others.

 

Ricketts(See also in 0-10 days bulletin)

Cause; Calcium or Vitamin D deficiency. Generally seen in birds slightly older than 10 days, but in severe cases may be younger.

Signs. Birds usually present with lameness and inability to walk or stand. Limbs may be bent.

It is because is usually dietary that it is seen at 2 to 4 weeks old. If the egg itself is very thin shelled, or the resorption of Calcium from the shell to the chick in late stage incubation is impaired, they may theoretically be born affected.

Spontaneous Fracture of the femur (thigh bone)

Cause. Vitamin C deficiency

Signs. Sudden onset lameness in groups of almost exclusively Grey (English) Partridges.

Treatment. Vitamin C and mineral mix in water

Staphylococcosis.

Cause. Infection by Staphylococcus bacterium

Signs. Poor growth. Increased mortality. Lameness. Swollen joints. (Fig 15). Nearly always a consequence of injury to the skin or mucosal membranes, poorly fitting bits and rough handling at bitting. Feather pecking also predisposes to infection.

Post mortem. Infection in joints, abscesses in the abdomen. Swelling around the beak.

Fig 15. Staphylococcosis. Swollen joints

Treatment. Unless picked up very early on, not much helps. Antibiotics in water can be helpful in treating birds just about to develop signs.

Prevention. Don't handle birds roughly. Avoid damaged wire in pens. Control feather pecking.

Streptococcosis.

Cause. Infection with Streptococcus family of bacteria. Route may be by damage to the skin (e.g. feather-pecking, exposed wire ends), ingestion or aerosol.

Signs. Most commonly presents as acute mortality in otherwise well growing younger birds. At post mortem an intense septicaemia can be seen throughout the body cavities.Bacteria may even be demonstrated in blood smears or bone marrow.

Treatment. Luckily most streptococci remain sensitive to many antibiotics, mainly of the penicillin family.

Prevention. Basic hygiene and avoiding risk of injury.

Yersinia (Pseudo-tuberculosis)

Cause. Infection by Yersinia pseudotuberculosis

Signs. Seen occasionally in Red Legged Partridge. Signs are very variable, varying from ill thrift to sudden death. Usually goes on for about 2 or 3 weeks. Will depend on which organs are most affected.

Post mortem. Widespread lesions can be seen in all the major organs. As its name suggests very difficult to tell apart from Avian tuberculosis. Absolute diagnosis depends on culture of the organism from affected birds.

Treatment. Of little value. Culling and thorough cleansing of the accommodation is most likely the best plan. No vaccine is currently available. As is so often the case, a vaccine for Gamebirds is unlikely to be developed because of the small potential market.

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