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Tuesday, February 26, 2013

The Avian Typhoid

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Control of salmonellosis shows results in the fight against avian typhoid

The first report of the avian typhoid was in England at the end of the 19th century. It is a diseases considered from the "developing" countries. In the United States of America, it is considered under control. This result is due to a national poultry disease prevention plan with emphasis on the control of salmonelloses. An important part of this plan refers to the elimination of infected birds, adoption of serological tests, research and identification of the Salmonella spp. serotype through bacteriological tests, completed with cleaning, disinfection and hygiene measures. In Europe, Germany and Denmark, the avian typhoid was noticed in the beginning of the 90s (20th century) and in the beginning of the current century. The disease has been observed in Mexico, South America and Asian countries. In Brazil, it has been diagnosed in areas of commercial layer exploration but it can also occur in breeders (broiler and layers).

Salmonella enterica subs enterica, sorovar Gallinarum biovar Gallinarum (SG) is the agent of avian typhoid. Just like S. Pullorum (SP), it has no flagellum. Both are indistinguishable in the basic serology for identification of the serotype (O: 1,9,12). They may differ bio-chemically. SG ferments dulcitol while SP does not. SP decarboxylates ornithine and SG does not. However, strains of SP that do not decarboxylate ornithine have been isolated. Based on the existing similarities, in the current classification, SG and SP are considered biovars of the Salmonella Gallinarum serotype.

Adult birds are more susceptible. However, they are not the only hosts

Chickens are the natural hosts of the avian typhoid agent. Nonetheless, other gallinaceous poultry are also considered susceptible, as well as other bird species. Palmipeds and pigeons seem to be resistant. The lighter lineages are considered the most resistant. In turn, the semi-heavy and heavy ones are considered susceptible to the disease. Birds of lighter lineages may develop the clinical disease. In the absence of the disease, these birds may host the SG in their bodies and spread the bacteria in situations of cannibalism.

Although it is more commonly observed in adult birds, the avian typhoid can affect birds of any age and can be mistaken for pulorosis in young birds.

S. Gallinarum has been naturally and experimentally isolated from other animals such as rats, chimpanzees, foxes, rabbits, guinea pigs and humans. In quails, it causes disease similar to that observed in chickens.

Transmission of the agent: can be influenced by different factors

According to specialized literature, the transmission of SG may occur through different routes, including the vertical route, which seems less probable. The bacteria can spread throughout the body of the animal during the disease, especially in the final phase when the bird is on the verge of death. The contact between the sick bird and the healthy bird, cannibalism and the presence of dead birds in the farm are factors that favor the transmission of the avian typhoid. Lack of hygiene and lack of cleaning, presence of flies, birds, vultures, rodents, etc. can contribute to the spreading of SG in poultry farms. Attention should also be paid in the use of compost and manure. Vehicles that transport birds, manure and eggs are also efficient means of spreading the bacteria, especially those that enter several farms without prior washing and disinfection (externally and internally). Individual that work in farms or that go to poultry farms can also act as elements that spread the avian typhoid agent. Multiple creations should also be avoided.

Clinical signs: morbidity and mortality can be high

The clinical manifestations are generally observed in adult birds. The birds remain quiet, prostrated, lay down, do not eat, experience yellowish-green to green diarrhea, there is an egg drop and in die within a few days. The course of the disease is 5 to 7 days but it may take longer. Morbidity and mortality can be high. Mortality varies from 10 to 80% (or even higher). In batches affected by the avian typhoid, the mortality does not occur all at once. In the beginning, some birds become sick and among these, some die. Then this condition repeats itself several times, in a way that a large part of the batch may be affected and then final mortality becomes significant.

When the disease affects young birds, it is mistaken for pulorosis, which is only differentiated after the isolation and identification of the agent.

Avian typhoid is a disease with characteristics of septicemia and toxemia. Congestion of the internal organs and anemia caused by the destruction of the red blood cells by the reticulo-endothelial system are observed. In acute cases, the changes are not very prominent. The liver and spleen increase 3 to 4 times the size. The liver becomes crumbly, greenish, yellow-greenish to bronze and full of necrotic (whitish) and hemorrhagic spots. The biliary vesicle becomes distended due to the increased volume of bile. The necrotic spots appear on the spleen and heart. Hemorrhagic spots are also observed on the spleen. In cases when the course of the disease is longer, hydropericardium and the presence of inflammatory processes forming whitish nodes similar to those described in pulorosis can be observed on the heart, spleen, lungs, gizzard, pancreas, duodenum and cecum. The inflammatory process in the heart may affect the pericardium, which makes it opaque, as well as the liquid in the pericardial sac. The kidneys may become yellow and the ovary atrophied or with hemorrhagic, shrunken, congested, cystic, deformed ovarian follicles, containing caseous or hemorrhagic material inside it, as it occurs in pulorosis. When light birds are affected by the disease, few become sick and die. However, experimentally infected birds developed lesions with egg drop but without experiencing mortality.

In avian typhoid, the presence of agglutinins does not mean protection. Although the antibodies take part in the fight against SG, the success depends mainly on cellular immunity. This control has bee attributed to the joint action of the reticulo-endothelial system (RES) and T. SG cells, for not having flagella, it induces a poor initial intestinal immune response (innate immunity), with low production of pro-inflammatory interleukins; which facilitates systemic infection. The expression of genes present SPI-2 and the genes spv present in SG also help inhibit the action of the immune system, potentializing the infection.

During the acute phase of the avian typhoid, accelerated multiplication of SG occurs inside the phagocytes. This results in cell lysis with the release of the bacteria to the extracellular medium, producing a kind of antigen-antibody reaction (anaphylactic hypersensitivity reaction). It also causes symptomatology and death. This reasoning was used to explain the condition of anemia of birds in avian typhoid. The destruction of the bacteria by lysis of the LPS results in the sequester of the fragments by the red blood cells and these are destroyed by the RES (macrophages). In a study with young birds experimentally inoculated with SG, a significant reduction of the circulating leukocytes was observed on the fifth day after infection. This finding was correlated to the mortality peak of the birds. Hence, it is assumed that the cytotoxic effect of the bacterial LPS is also responsible for the lysis of the leukocytes.

Final diagnosis consists of the isolation and identification of the agent

The diagnosis of the avian typhoid is performed based on the clinical, anatomopathological and lab test findings. Birds infected for periods of over two weeks are positive in the pulorosis test. The results are liable to be mistaken with birds infected by SP or by another salmonella that has antigens in common, such as those in group D. An immunoenzymatic test (ELISA) can present more specific results but without differentiating the response between birds infected by SG or SP.

The final diagnosis consists of the isolation and identification of the agent. The bacteriologic procedure is the same adopted for SP. The behavior of these two salmonellas is very similar. Both produce small colonies in selective agar mediums (SP produces smaller colonies than SG) and produce few or almost no H2S in TSI agar. The elected organs for research of the agent are the same inspected for the pulorosis agent, highlighting the spleen, liver and heart. Besides pulorosis, the differential diagnosis should be performed in relation to other salmonelloses, colibacillosis, pasteurellosis and Marek's disease. Molecular tests have been adopted to differentiate SG from SP.

Major ally in the treatment is the adoption of efficient cleaning and hygiene measures

Once the disease is more common in adult birds and the mortality can persist for extended periods, care is necessary to prevent intoxication of the birds with the prolonged administration of antimicrobials. Even in the presence of an outburst of avian typhoid, the biggest ally of the treatment is the adoption of efficient cleaning and hygiene measures and the fast and correct elimination of the dead birds. Consider that SG persists in treated birds that experience no symptomatology.

The best prevention program is based on cleaning, hygiene and disinfection of the farm. Care must be taken with dejects, to avoid stagnant water, have the correct and fast destination of dead animals, with vehicles that transport the birds, feed and their raw materials, feces (bed) and eggs, among others. Avoid birds, rodents, mosquitoes, other species of birds and other animals. Avoid birds of different ages. Monitoring of the farm routine should consist of microbiological test on the birds that died. It is recommended to use vaccinal programs as long as the general biosafety procedures are not forgotten. Live and inactivated (bacterial) vaccines are available against this disease. Among the live vaccines, the most commonly known is the 9R.

By Angelo Berchieri Júnior and Oliveiro Caetano de Freitas Neto, of the Faculty of Agricultural and Veterinary Science - Unesp - Jaboticabal (SP).

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