Dealing with LT: When Biosecurity Matters Most

An avian disease the chicken community is familiar with -- laryngotracheitis (LT), a highly contagious respiratory disease affecting chickens -- is affecting several Delmarva farms this fall. Growers, chicken companies, and allied businesses servicing farms and farmers all have a role to play in preventing the spread of LT, and the current cases underscore how essential it is to practice good biosecurity at all times, not only when an outbreak commands our attention.

What LT is

LT is caused by a herpes virus and can cause very high mortality in broiler flocks. Chickens infected with LT experience a sudden increase in mortality occurring from 5 to 8 weeks of age. Morbidity is usually high and mortality progresses in a doubling pattern each day and may peak as high as 50/1000 (5%) per day. Death losses may continue for up to two weeks and the feed conversion rate of surviving birds is negatively impacted.

Signs of LT include respiratory distress including coughing, gasping, and swollen wet eyes (conjunctivitis). Birds "crowing" may also be heard. Lesions of necrotic tissue and blood in the trachea are diagnostic for LT. See image below.

How LT spreads

Incubation period in the disease process is when the virus is actively replicating and shedding in the bird, but before the appearance of clinical signs. The incubation period for LT is 8 to 14 days - a wide window when birds are sick but don't appear sick.

LT can easily be spread from farm to farm. Two patterns of infection are common: "walk in" or "aerosol". A "walk in" pattern of infection occurs when clinical signs of LT first appear in birds located near the entrance door used by poultry house workers. This is a strong indication of people spread of LT and is most commonly observed. A less common "aerosol" pattern of infection occurs when the first clinical signs of LT are observed in birds located along the sidewall of the house near air inlets, often on the side of the house nearest to the road. This may be an indication of aerosol spread of LT.

Mortality and litter management is key

Birds that have died from LT infection contain large numbers of infectious virus, so proper management of dead birds is critical.

  • Dead birds should never leave an infected farm.
  • Growers should never have contact with dead birds from other farms. Such contact may occur via shared composters, shared manure sheds, rendering plant pickup sites, illegal feeding to hogs, or at diagnostic laboratories.
  • Spreading of fresh poultry litter from flocks known to be infected with LT should be strictly avoided. Aerosol exposure to LT may occur from the spreading of LT-positive litter nearby.

Consistent biosecurity protocols protect the flock

Control of LT is achieved via sound biosecurity practices supplemented with vaccination in the field where necessary. To best protect your farm from LT and other viral diseases, the following procedures should be carefully, consistently followed.

  • Do not allow visitors to enter poultry houses.
  • Do not visit other poultry farms.
  • Require that any equipment used on your farm be cleaned and sanitized prior to arrival.
  • Require that necessary visitors wear proper biosecurity clothing and footwear.
  • Wear dedicated footwear inside poultry houses. Shoes that are worn inside poultry houses should never leave the farm - simply change into the same shoes prior to working inside the poultry house. This simple footwear policy will prevent you from tracking disease from another location back to your farm on the bottom of your shoes. (Poultry manure may contain millions of virus particles!)
  • Never transport dead birds off of your farm or allow anyone onto your farm to pick up and remove dead birds. Dead bird collection areas are highly contaminated with viruses, and the risk of bringing or back tracking a disease problem to your farm is extremely high from this activity.

Swollen, wet eyes, or conjunctivitis, in a chicken infected with LT. Image: University of Maryland Extension.

About Delmarva Chicken Association
Delmarva Chicken Association, founded in 1948, is the Delmarva chicken industry's voice as the premier membership association focusing on advocacy, education and member relations. DCA's vision is to be the most-respected chicken organization in the United States. For more information about the Delmarva Chicken Association, visit or call 302-856-9037.

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