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Vaccination: effective measure against fowl typhoid21/04/2021
Brazilian heat is very challenging for egg producers. This is because laying hens, animals covered by feathers, have few means to adapt quickly to the high temperature and humidity characteristic of the season.
Intense heat, when it exceeds a threshold of thermal comfort, forces the bird to keep its beak open and its breathing wheezing. It starts to consume more water and less feed, which changes its metabolism and leads to a condition called “heat stress”.
The result is the loss of flock productivity and impaired bird immunity. When the defense cells of the laying hen are at a low level, the increase in bacterial pressure causes the bird to become ill and, subsequently, to die.
The death rate, which is initially discreet, starts to increase, which indicates that there is some serious disease present in the flock. It is generally in this scenario that fowl typhoid appears on the poultry farm.
What is fowl typhoid?
Fowl typhoid is a disease of great importance and reason for attention for laying poultry. To give you an idea, it is estimated that the death rate ranges between 40 and 80% of the poultry flock, causing great economic loss.
It is a systemic, acute/chronic and devastating septicemic disease, more common in adult birds, but affecting any age. As the problem is recurrent, attention to monitoring and measures to control the disease must be constant.
Although summer is the most favorable season for infection, because of the heat and high humidity, it can appear at any time of the year and persist for months in the flock.
Action of Salmonella Gallinarum bacterium
Fowl typhoid is caused by the enterica subspecies serovar Salmonella Gallinarum, with the fecal-oral route being the main means of infection. Salmonella bacterium has two classifications: paratyphoid and typhoid. While the first group does not produce clinical signs or injuries, the second group (from Salmonella Gallinarum) is a cause for concern in commercial laying hens.
In it, the bacterium is first phagocytized by antigen-presenting cells in the lymphoid tissues of the intestine and then “presented” to macrophages – the cells of choice in defense against Salmonella Gallinarum.
It is through the endothelial reticulum system that the typhoid bacterium access secondary lymphoid organs, such as the liver and spleen. When multiplying, two scenarios can occur:
- immune system cells control that multiplication and cause the bird to recover;
- multiplication reaches the bird blood, becomes generalized and it dies.
The disease severity depends on the dose – it varies according to the age of the birds. The disease starts at a farm place and spreads when the birds start pecking at the dead animal carcass.
That is, the longer the contaminated carcass remains in the environment, the greater the spread of the disease agent.
What are the fowl typhoid symptoms?
Birds affected by fowl typhoid stop feeding, become retracted and prostrated, may have a head and neck tremor and have greenish-yellow diarrhea.
The diagnosis of fowl typhoid is made based on clinical, anatomical and pathological findings and laboratory tests. And, despite the septicemia, that is, the disease affects several organs at the same time, the ones in which more changes are observed are the liver and the spleen.
They have increased volume, splintering and the color ranging from yellow to greenish-yellow or yellow-tan – the change in color is easier to see when exposed to sunlight. It is also possible to find hemorrhagic spots and yellowish-white spots – necrotic spots.
The ovary may become congested, the gallbladder distended, the lung with whitish areas and the heart with whitish areas and hemorrhagic and necrotic spots.
White Egg layer hens are more resistant
Fowl typhoid affects chickens in general, with hens, turkeys and quails being the most susceptible. However, the clinical signs and mortality, vary according to the color and weight of the birds. It is observed that in Brown Egg layers and Broiler breeders, the propensity to mortality is greater.
But that does not mean that care for White Egg layer hens should not exist. If the bird becomes contaminated and dies, for whatever reason, Salmonella Gallinarum spreads through the carcass and becomes a source of infection for other birds.
The broiler breeders are in a situation closer to Brown Egg layers.
Is there treatment for fowl typhoid?
The antibiotic treatment decreases mortality temporarily, but it does not eliminate the bacterium from the flock. Once contaminated, the chickens remain with Salmonella Gallinarum and the disease can return at any moment – generally in stress situations.
Biosecurity, then, is a great ally in the prevention and control of an outbreak of fowl typhoid. Based on the principles of the least possible spread of the bacteria within the environment, the main measures are:
- Systematic and persistent control of insects, mites and rodents;
- Cleaning and disinfection programs in general;
- Entry restriction and access flow change in flocks infected by fowl typhoid;
- Implementation of measures that reinforce the disinfection of vaccination and maintenance equipment and teams, removal of manure and others that enter and leave contaminated houses;
- Placing sanitary barriers reinforced with alcohol gel and hand and shoe sole sanitizers;
- Removal — as soon as possible — of the dead bird from the cage and house. If it is dying, it is best to remove it before it even dies. It is always advisable to handle with asepsis and give the bird or carcass the appropriate disposal; the most indicated is that they are incinerated and not disposed of in pits or composters.
As the carcass has a relevant role in the spread, it is necessary to neutralize this source of infection. It is extremely important to remove dead birds from the house more often, preferably as many times as possible during the day.
The carcass must be protected from insects, wild animals, rodents, humans, domestic animals, etc. The use of buckets with lids or plastic bags help to seal the carcasses until they are removed from the house.
Their treatment, whether by incineration, dehydration, etc., must be monitored by means of a bacteriological test to confirm the effectiveness in the elimination of Salmonella Gallinarum. On the poultry farm, it is necessary to clean and disinfect the place where the sick bird was and observe the animals that were nearby, eliminating them quickly, if necessary.
But there is an initiative that needs to be aligned with biosecurity measures and gives even more protection to birds against fowl typhoid: vaccination. Live vaccines attenuated with the rough strain SG 9R stimulate the bird’s immune system to produce defense cells and antibodies against the bacterium Salmonella Gallinarum.