MY CHICKEN HAS A COLD - PART III
by K. J. Theodore
Chickens do not suffer from the Common Cold. Your bird may have one of many upper respiratory ailments, such as Infectious Coryza, Infectious Bronchitis, a CRD, or perhaps some other form of respiratory distress including bacterial, fungal, or viral infection – perhaps even something like Laryngotracheitis (commonly known as Laryngo ‘la-reeng-go’). But chances are, they don’t have the Common Cold.
I’ve already written about Infectious Coryza and Bronchitis. This article will address another possibility, LARYNGOTRACHEITIS (or Laryngo), since there is some confusion about whether or not to vaccinate, along with the different methods of vaccination available.
Laryngo (or LTV) is a common viral respiratory infection of the Herpesviridae. This Herpes virus infection is isolated almost exclusively to the chicken, although other species have shown some rare vulnerability. Adult birds appear to be the primary target of the virus and meat-type males appear more susceptible than meat-type females. All breeds have a higher death rate when under heat stress.
LTV is found worldwide with most commercial flocks in the US remaining under control through vaccination and isolation programs, including strict biosecurity practices. The common backyard flocks, along with Fancier (exhibition) flocks, being at the highest risk for unintended exposure through both exhibition and the introduction of the virus through the purchase of birds that carry the virus.
The primary target of LTV (much like Infectious Bronchitis) is the trachea, with the primary symptoms being moist tracheal rales, nasal discharge, and most notably (in severe cases), a bloody discharge from the nose and/or mouth. This element is significant since the presence of blood from mucous discharges and coughing/sneezing, can be a defining symptom when attempting to diagnose LTV in a flock that exhibits upper respiratory symptoms. In other words, when diagnosing specific upper respiratory infections, which are sometimes difficult to differentiate, LTV should be ruled out first when blood is present. Other similar differentiating symptoms include face swelling and/or odor to Infectious Coryza, and a rapid rate of spread with Infectious Bronchitis. (There are always exceptions to these guidelines when diagnosing, but they represent a good starting point for the process of elimination.) Other symptoms for LTV are coughing, gasping, reduction in production, watery eyes and conjunctivitis, and swollen sinuses.
LTV (in its mild form) is not as contagious as something like Infectious Bronchitis, with only about 5% of the flock becoming ill and a very low death rate. However, more severe LTV infections can cause illness in 90-100% of the flock with variable death rates. The incubation period is believed to be somewhere between 6 to 12 days and can be spread by infected birds and/or mechanical means. It does not pass vertically (to the egg). LTV is somewhat easy to kill with common disinfectants and/or heat. As part of any good biosecurity program, you should also prevent the movement of rodents through the coop.
One way to fight an active outbreak of LTV is to consider vaccinating the entire flock on an emergency basis. Doing so can reduce the number of birds infected, as well as reduce the duration of the illness. This is where the understanding of the vaccination issue is important. My subsequent comments are generalized and do not take into account any State specific regulations. Any time you consider a vaccination program, you should contact your State agency to determine if your program would be in compliance.
Since the vaccination against LTV using a modified-live vaccine can result in creating carriers, vaccination is probably best reserved to areas where it is either required by the State or where LTV is known to be prevalent. TCO-LT (Tissue Culture Origin) vaccines are considered to be the vaccine of choice when attempting to prevent setting up a carrier state in your flock (although still possible). CEO-LT (Chicken Embryo Origin) vaccines are more likely to set up a carrier state, as well as create a more virulent strain of virus as it passes through each bird (virus spread ‘in-vivo’ – bird-to-bird passage). After as few as 10 sequential passages in chickens, the increased virus virulence is equal to that of a highly virulent strain (IL N71851). Vaccination with one specific strain seems to provide protection from all strains. However, there remains some question as to how long any vaccination against LTV is effective (outbreaks have occurred in vaccinated flocks after 20 weeks). The effectiveness of boosters at this time is unknown. Also, the drinking water method of vaccination seems to be less effective overall than other methods.
If you decide to vaccinate against LTV, then I recommend that you inform others that you do if you sell or give away birds. Birds vaccinated with the CEO-LT type vaccine should not be shown.
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