Poxvirus in Chickens

 

By Dr Rob Marshall

 

Pox is a common viral disease of all varieties of poultry. Because Pox is a slow spreading disease there is ample opportunity to stop the spread of infection. This is achieved by immediately vaccinating the entire flock at the first sign of the disease. In order to prevent pox outbreaks it is important to eradicate those insects (mosquitos and fowl mites) that help transmit the disease. Prevention is also aided by limiting overcrowding as wounds received whilst fighting helps spread the disease. Regular cleaning of the pens of feathers and dust is needed during the moult, in order to reduce the opportunity of the virus to accumulate in the environment. This measure will help reduce thwe likelihood of the wet more and serious form of Pox which is spread through contaminated aerosol.

Pox begins as progressive yellow wart like eruptions on the skin (wattle, comb, eyelids, beak, mouth, feet, legs and ears) and as curd-like yellow tags in the mouth (especially the corners of the mouth and alongside the tongue closely resembling canker or thrush infections). The skin form occurs more commonly during the warmer months whereas the mouth form occurs when it is cooler. On the skin the sores develop wart-like scabs that are of no real harm to health. These sores usually fall off after a month. However, pox sores in the mouth, throat, crop, eyes and trachea seriously affect the health of chickens and are often fatal.

 

Symptoms

 

There are two forms of Pox in chickens:
 

1. Dry or Skin Form
   
   This form produces crusty or ulcerated sores on the non-feathered parts of the body (comb, wattle, eyelids, head, face and feet). Birds infected with this form are more likely to recover. The course of this type of pox infection is 3-4 weeks.
    

2. Wet or Diptheric Form
   
   This form is more serious and creates sores in the mouth, throat, esophagus and upper respiratory tract producing coryza-like symptoms. Birds infected with this form are less likely to recover as the sores interfere with eating, drinking and breathing.

 

Pox Prevention

 

Annual vaccination is recommend in flocks that have experienced recurrent outbreaks. Chickens should be vaccinated each Christmas prior to the heavy body moult. Vaccination is not necessary in flocks taht have not experienced pox outbreaks.

The success of vaccination depends upon the potency and purity of the vaccine and its application. All birds must be vaccinated on the same day. The dry vaccine pellet must be stored in the freezer and is mixed with the water vial to produce the active vaccine on the day of vaccination. The reconstituted form is active for only 12 hours (refrigerated or not). The best response to vaccination requires that the vaccine comes in contact with a blood vessel. The wing stab method is a reliable vaccination technique for chickens. Within a week there is a local raised tissue reaction in the web that signifies the vaccine has been effective. The vaccine produces a fever 5-10 days following the vaccination, during which time the birds may become quiet and go off their feed for a day or two. During this fever stage there may be a halt to egg laying and the birds' droppings become more watery. It takes up to 3 weeks for the flock to return to normal activity following vaccination. However, at this time the flock should appear healthier than before the vaccine. This positive response to pox vaccination occurs because the vaccination process stimulates the immune system. In a flock that is unwell the vaccination will precipitate illness in weak individuals. When thids occurs additional treatment for underlying problems is required.

 

Pox Treatment During an Outbreak

 

Treatment for Individual Birds with Pox Sores

 

• Identify and isolate all birds with Pox sores. Pox sores will enlarge for 2 weeks then gradually regress over the following 4 weeks with treatment.

 

• Use Betadine iodine on a cotton bud each day to dry and cleanse the pox sores. Gently clean the surfaces of the skin and mouth sores with the cotton bud but be gentle to avoid bleeding. The scab will fall away within a few weeks time.
   

• Dose severely infected birds with an appropriate antibiotic tablets for 5 days.
   

• Add an appropriate disinfectant to the drinking water for 10 days to kill the virus and to prevent infection.
   

• Clean the pen of all feathers and dust as these are a common source of wet pox infections. Then disinfect the pen each week for four weeks with an appropriate disinfectant.
   

• Crop feed important birds if necessary. Cull those birds that fail to eat properly within 2 weeks.
   

• Apply a suitable antibiotic eye cream to dry up infected eyelid sores. Cull birds with serious eye and beak abscesses.

 

Treatment for the Rest of the Flock

 

• Vaccinate all healthy birds. The vaccination protects the flock and limits the spread of the disease. Expect pox sores to appear in a small proportion of the healthy birds for a week or so after vaccination. Fortify diet to protect the flock during this interim period.

 

• Disinfect the pen each week for 3 weeks.