Un­der­stand­ing in­fec­tious laryn­go­tra­cheitis

Res­pi­ra­tory dis­ease leads to se­vere losses

The Poultry Bulletin - - CONTENTS -

Re­spon­si­ble for ma­jor losses in the poul­try in­dus­try, In­fec­tious Laryn­go­tra­cheitis or ILT is an acute res­pi­ra­tory dis­ease caused by a her­pes virus. Although peo­ple are not af­fected by ILT and be­cause cook­ing de­stroys the virus, it is safe to eat poul­try prod­ucts from in­fected birds. But the most se­ri­ous threat is to the flock it­self - with deadly out­comes.

ILT usu­ally kills be­tween 10% and 20% of in­fected birds, although mor­tal­ity can run as high as 70% in some cases. It is found in most ar­eas where chick­ens are raised. In­fected chick­ens serve as the pri­mary source of in­fec­tion when they shed the virus and trans­mit it to other chick­ens through res­pi­ra­tory se­cre­tions, and from cough­ing and sneez­ing.

Peo­ple who work with Ilt-in­fected poul­try can spread the virus through con­tam­i­nated hands, footwear, cloth­ing, equip­ment, ve­hi­cles, lit­ter, and other me­chan­i­cal vec­tors. Im­prop­erly dis­posed chick­ens that die from ILT can serve as a source of in­fec­tion, es­pe­cially through scav­engers like do­mes­tic dogs and wild an­i­mals. Re­cov­ered and vac­ci­nated chick­ens can also serve as car­ri­ers of ILT and can shed the virus when they are sub­jected to stress­ful con­di­tions.

ILT signs

Clin­i­cal signs (as de­scribed be­low) usu­ally ap­pear 6 to 12 days af­ter ex­po­sure to ILT virus. This time in­ter­val is called the in­cu­ba­tion pe­riod and will vary ac­cord­ing to the amount of virus and other fac­tors such as the im­mune sta­tus of the chicken, en­vi­ron­men­tal con­di­tions (such as high lev­els of dust and am­mo­nia), and con­cur­rent in­fec­tion with other bac­te­ria and viruses.

Chick­ens suf­fer­ing from a mild form of ILT usu­ally have swollen, wa­tery eyes (con­junc­tivi­tis), swollen si­nuses, and a per­sis­tent wa­tery or mu­coid nasal dis­charge (Fig­ure 1). These clin­i­cal signs are sim­i­lar to other res­pi­ra­tory dis­eases of poul­try. Chick­ens with a se­vere form of ILT ex­hibit la­bored, open-mouth breath­ing (Fig­ure 2), fre­quent sneez­ing, and vi­o­lent cough­ing, of­ten ac­com­pa­nied by bloody mu­cus. These chick­ens will usu­ally shake their heads to clear the mu­cus from their nose and mouth, re­sult­ing in blood­stained mu­cus on their feath­ers and on the walls of the chicken house or shed.

Run­ning the course

The course of the dis­ease ranges from 10 to 14 days but de­pends largely on the sever­ity of clin­i­cal signs and le­sions. Chick­ens that ex­hibit open-mouth breath­ing and cough­ing of bloody mu­cus usu­ally die within a few days, but those with mild clin­i­cal signs are more likely to re­cover.

The sever­ity of the clin­i­cal signs and le­sions is re­lated to the mor­tal­ity seen in flocks with ILT. Mild forms of the dis­ease re­sult in very low mo­ral­ity (0.1-2%). Se­vere forms of the dis­ease re­sult in vari­able mor­tal­ity (5-70%), with the av­er­age be­ing 10-20%.

Di­ag­nos­ing ILT

In ILT in­fec­tions, clin­i­cal signs alone should make you highly sus­pi­cious. Even so, as with any dis­ease, you should sub­mit birds to the di­ag­nos­tic lab­o­ra­tory in your area for con­fir­ma­tion of the di­ag­no­sis. A post-mortem ex­am­i­na­tion of af­fected birds will gen­er­ally re­veal blood in the bird’s air­way. The tra­chea or wind­pipe is of­ten very bloody and may be par­tially clogged with mu­cus and blood (Fig­ure 3). Swabs of the tra­chea will be used to at­tempt to grow the virus. Other di­ag­nos­tic tests may be per­formed to con­firm that your flock has ILT.

Pro­tect­ing the flock

There are dif­fer­ent types of vac­cines that can be used to con­trol ILT. Own­ers should con­sider the tis­sue cul­ture ori­gin (TCO) vac­cine, which is ad­min­is­tered by sim­ple eye drop. Ad­min­is­tra­tion of this vac­cine should oc­cur at least 30 days prior to shows and fairs. As with all avail­able vac­cines, the la­beled di­rec­tions for use and ad­min­is­tra­tion must be strictly fol­lowed.

The in­tro­duc­tion of ILT and other dis­eases onto your farm and into your flock should be the goal of all pro­duc­ers. It is not dif­fi­cult to do if you fol­low some com­mon sense guide­lines. Don’t move any birds on or off your farm dur­ing an ILT out­break; and don’t visit other poul­try farms, fairs, auc­tions, or ex­hi­bi­tions dur­ing an ILT out­break.

Im­ple­ment sim­ple biose­cu­rity mea­sures that can be taken to help pro­tect flocks. Buy a pair of rub­ber boots and wear them only on your own premises, to avoid ‘track­ing in’ dis­ease. Use a long-han­dled brush to scrape off ma­nure, mud or de­bris from tyres, equip­ment or boots, and then dis­in­fect. Mix three parts bleach to two parts wa­ter, and use it lib­er­ally to clean rub­ber boots and equip­ment brought onto your farm. If vis­i­tors don’t want their ve­hi­cle tyres sprayed with dis­in­fec­tant, ask them to park out­side your gate. Don’t be shy about ask­ing vis­i­tors to dis­in­fect their footwear. Bet­ter yet, pro­vide guests with dis­pos­able shoe cov­ers, or footwear worn only on your place.

Fig­ure 1. Swollen, wa­tery eyes

Fig­ure 3. Tra­chea filled with blood and mu­cus

Fig­ure 2. Open-mouth breath­ing

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