10 THINGS EV­ERY CHICKEN OWNER SHOULD KNOW ABOUT MAREK’S DIS­EASE

Just the men­tion of Marek's dis­ease arouses dread in many poul­try keep­ers, but there is a lot of mis­in­for­ma­tion around which only serves to en­hance those fears. Words

NZ Lifestyle Block - - Your Poultry - Sue Clarke

BE­FORE SCIENCE knew its name or what the causative agent was, Marek's was known by var­i­ous terms, among them new pul­let dis­ease, range paral­y­sis and grey eye. To­day we know a lot more about this nasty virus.

1 TH­ESE BIRDS ARE MOST AT RISK

It typ­i­cally af­fects young birds from about 10 to 25 weeks old and 25% mor­tal­ity is not un­com­mon in un­vac­ci­nated birds dur­ing the rear­ing stages. Chicks are most sus­cep­ti­ble from one-day-old and for the first month of life, how­ever the dis­ease symptoms may not man­i­fest them­selves for many weeks, most com­monly 10-25 weeks.

2 MAREK’S IS CAUSED BY A HER­PES VIRUS

The dis­ease was named af­ter József Marek, a Hungarian vet­eri­nar­ian, and is caused by a highly con­ta­gious vi­ral dis­ease of the Her­pes fam­ily. It is pri­mar­ily only a dis­ease of do­mes­tic chick­ens, although in­fec­tion has been re­ported in other avian species and a re­lated Her­pes virus found in turkeys which causes no ap­par­ent dis­ease in turkeys can be used as a vac­cine (HVT) for chick­ens.

3

VAC­CINES ARE FAIRLY NEW

A vac­cine for Marek's dis­ease has only been avail­able since 1970. Prior to this it was nor­mal for world poul­try farm­ers to have sig­nif­i­cant losses from Marek's dis­ease, so al­most all com­mer­cial lay­ing hens were vac­ci­nated once it was dis­cov­ered. How­ever, there was a resur­gence of the dis­ease in the mid-1980s and a new vac­ci­na­tion pro­gramme was de­vel­oped to cope with new vir­u­lent strains. It is now com­mon prac­tice to vac­ci­nate the par­ent breed­ing stock of com­mer­cial lay­ing birds with a dif­fer­ent vac­cine to that which is used on their off­spring.

4 VAC­CINES CAN’T WORK FOR THE AV­ER­AGE BACKYARD FLOCK

Marek's vac­cine is read­ily avail­able but it comes in vials with a 1000 dose min­i­mum for one-day-old chicks. Once mixed with the dilu­ent, it must be swirled gen­tly ev­ery five min­utes, and the bot­tle must be com­pletely used up within 24 hours of be­ing opened, mak­ing use of vac­cine by the small poul­try keeper vir­tu­ally im­pos­si­ble. There are a few other re­stric­tions which makes Marek's vac­ci­na­tions an un­suit­able process for small flock own­ers (see box at 58).

5 MAREK’S DIS­EASE IS MUCH MORE COM­MON THAN YOU THINK

There is a say­ing ‘if your chicken breathes it has been in con­tact with Marek's dis­ease' so no mat­ter how strin­gent your clean­ing or pro­cesses, you can't stop birds get­ting Marek's dis­ease.

6 IT’S A DOU­BLE WHAMMY FOR AN IN­FECTED BIRD

Marek's su­presses the im­mu­nity of a bird, in­creas­ing its sus­cep­ti­bil­ity to other dis­eases such as coc­cid­io­sis.

7 IT IS NOT EGGTRANSMITTED

Marek's can­not be passed by the mother through the shell. It is shed in skin par­ti­cles and in cells as­so­ci­ated with the feath­ers.

8 THE DIS­EASE HAS A LONG IN­CU­BA­TION PE­RIOD

This can be up to three months or longer, and it can man­i­fest it­self in three dif­fer­ent ways:

1. NER­VOUS (NEU­RO­LOG­I­CAL) - paral­y­sis of the legs/wings,eye le­sions. 2. VIS­CERAL - tu­mours of the or­gans and mus­cles.

3. CU­TA­NEOUS - tu­mours of the skin and feather fol­li­cles.

The vac­cine pre­vents the for­ma­tion of tu­mours but it does not pre­vent the in­fec­tion and shed­ding of the field virus by the chicken. Even vac­ci­nated birds may ex­hibit other clin­i­cal symptoms un­less

at­ten­tion is made to good hy­giene. It is es­sen­tial to place the vac­ci­nated day old chicks into a clean en­vi­ron­ment where there is no chal­lenge by the virus.

9 SOME BREEDS ARE MORE SUS­CEP­TI­BLE

Some breeds and even strains within a breed may be more sus­cep­ti­ble to Marek's dis­ease and cer­tain blood groups may also ge­net­i­cally have bet­ter

re­sis­tance, depend­ing on:

• the level of ma­ter­nal an­ti­bod­ies in their

sys­tem;

• their ge­netic re­sis­tance or sus­cep­ti­bil­ity

- Silkies and White Leghorns ap­pear to be

more prone to Marek’s dis­ease, but some

strains will be more sus­cep­ti­ble;

• the con­tam­i­na­tion in their en­vi­ron­ment;

• early chal­lenge to dis­eases like

coc­cid­io­sis, in­fec­tious bron­chi­tis or other

im­mune-low­er­ing con­di­tions.

10 THERE IS NO EF­FEC­TIVE CURE

Sup­port your birds with a warm, dry, airy (but draught-free) living area, ap­petis­ing food (eg, their usual pel­lets and some­thing high in pro­tein like dog roll or cat food), a vi­ta­min sup­ple­ment like Poly Aid Plus (see your vet or pet store), and hand-feed­ing a bird that is paral­ysed. A small per­cent­age of birds may sur­vive, and if they do they will be im­mune to Marek’s.

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