Antibiotics in animal production have been under fire in recent years for reasons of public health. Particularly the EU is taking the lead in this respect. Their use must be limited. Despite proper management and biosecurity measures however, certain diseases and syndromes like in turkeys need antimicrobial control.
By Prof Hafez Mohamed, Hafez Institute of Poultry Diseases, Free University Berlin, Germany
Turkey diseases remain of major economic and public health importance. Diseases are mostly accompanied with increased mortality rates, decreased weight gain, decreased egg production, and increased medication costs. In addition, in recent years, public health problems associated with foodborne infection in poultry and antibiotic resistant strains have increased to the extent that they have become major political issues of which the general public in several countries have been aware. Several infections, pathogenic bacteria and to lesser extent parasitic infestations are requiring antimicrobial therapy and/or control. However, bacteria can easily acquire new antibiotic resistance genes. Among recent examples in poultry are Vancomycin-resistant Enterococci, Methicillin-resistant Staphylococcus aureus, Campylobacter as well as Extended-spectrum β-lactamases (ESBL) bacteria multi resistance.
Vertical and horizontal
Currently the most important disease complexes are respiratory and intestinal disorders. Several bacterial pathogens are incriminated as possible causes of respiratory diseases and enteric disorders (Table 1), either alone (mono-causal) or in synergy with other micro-organisms (multi-causal) or accompanied by noninfectious factors such as climatic conditions and management related problems.
These infectious agents can be introduced and spread in poultry farms by different routes. It occurs by vertical and/or horizontal route. At early days of age the main disease problems are related to vertically transmitted infections such as Mycoplasma, salmonella, E. coli or improper hatchery management. Those and other infectious agents can also be transmitted horizontally (laterally) by direct contact between infected and noninfected susceptible birds, and through indirect contact with contaminated feed, water, equipment, environment and dust through ingestion or inhalation.
The diagnosis of the disease complexes is not usually a straightforward business. Beside the multifactorial nature of many infectious diseases there are also a lot of less defined problems. Basically the diagnosis consists of case history as well as management and environmental investigation on spot. In addition, clinical investigations and post-mortem examination done on the farm is an important step toward disease diagnosis. However, clinical signs and necropsies are mostly not the final step of the diagnosis. The final diagnosis can only be reached by laboratory diagnosis.
Sound management practices
Disease prevention and control focuses primarily on dedicated planning and sound management practices, which prevent the introduction and spread of infectious diseases. This includes managing the environment by supplying adequate ventilation and heat to maintain bird comfort, to keep the litter in good condition, insure supplying fresh feed and water with good quality, and limiting exposure to infectious agents through biosecurity, cleaning and disinfection, vaccination and supportive therapy. In addition, early recognition and monitoring programmes are essential in managing the infectious diseases, minimising the economic impact and reducing the use of antibiotics.
Vaccination is regarded as one of the most beneficial biopharmaceutical interventions, due to its ability to induce protection against infectious diseases through activation of the immune system. However several considerations should be taken into account before using vaccines such as: governmental regulations, epidemiological situation in the area and/or on the farm, goal of vaccination, availability of the vaccine and cost benefit analysis. Progressive vaccine production technologies such as recombinant, subunit, reverse genetic and nucleic acid vaccines can significantly reduce the cost of vaccines, ensure better efficacy and allow easy and rapid intervention to face the steady mutation of the microorganisms. Furthermore, the development of efficient vaccines against bacterial infections will lead to a reduction of the use of antibiotics and subsequently of the development of resistant bacteria.
Antimicrobials are important and are essential tools to control bacterial infectious diseases, if the above mentioned measures did not prevent the infection in aim to insure health of the flock and to enhance the welfare and to reduce the economic losses. In such cases, therapy should be considered as the last effective weapon, but treatment without accurate diagnosis, critical selection of the product, accurate dosage, adequate duration and monitoring treatment is unacceptable. In addition, if necessary as in case of treatment failure, corrective action should be taken.
Finally, since the success of any disease control programme depends on the farm and personal sanitation, it is essential to incorporate education programmes about micro-organisms, modes of transmission as well as awareness of the reasons behind such control programmes by people involved in poultry production.In the space available, it is not possible to review extensively all bacterial emerging diseases that cause problems for the poultry industry worldwide. This article explores some of these problems, their economic impact and control approaches.
Ornithobacterium rhinotracheale (ORT)
This infection has been recognised in many countries worldwide and is incriminated as a possible additional causative agent in respiratory disease. The disease is spread horizontally by direct and indirect contact. Vertical transmission is suspected.
Currently 18 serotypes designated A to R seem to exist. Neither the origin nor the serotype of the O. rhinotracheale strains have an effect on the pathogenicity. There are many reports showing synergism between ORT and Newcastle disease, turkey rhinotracheitis, Infectious bronchitis, Bordetella avium, Escherichia coli, Mycoplasma gallispeticum as well as Chlamydia psittaci.
In turkeys outbreaks mostly have been observed in male birds over 14 weeks of age. However in many cases young poults between the second and eight week could also be found to be affected. The mortality ranges between 1-10% during the acute phase (8 days). Initial symptoms are coughing, sneezing and nasal discharge followed in some cases by severe respiratory distress, dyspnoea, prostration, sinusitis and arthritis. The incidence of ORT associated arthritis has increased in the recent years. The symptoms are accompanied with a reduction in feed consumption and water intake. In 2002, Szalay and co-workers observed nervous manifestation in one flock of 5-week-old poults and in three 16- to 20-week-old turkey flocks. The symptom was accompanied by increased mortality and was found to be associated with fibrino-purulent inflammation of the cranial bones and meningitis and the bacteria could be isolated from the lesion.
Control and treatment
ORT is highly sensitive to chemical disinfectants. However, ORT is endemic and can affect every restocking even in previously cleaned and disinfected houses especially in areas with intensive poultry production as well as in multiple age farms. Failure to clean and disinfect properly after an infected flock has left, can cause infection of the neighbouring houses and the causative agent can continuously cycle from house to house.
Several attempts to combat the infection using vaccines were carried out with different results. In the field, vaccinations with autogenous inactivated oil-adjuvant vaccines are currently widely used in Germany and are proven to be successful in reducing the outbreaks of ORT.
The treatment of ORT infections is very difficult because different strains have variable susceptibilities to antibiotics. ORT acquires resistance against antibiotics easily. The sensitivity pattern depends on the source of the strain and the routinely used drugs in an area. It should be emphasised that for successful treatment an investigation of the sensitivity pattern of the isolated strain is necessary.
Infections with Clostridium perfringens in poultry can cause several clinical manifestations and lesions include necrotic enteritis, necrotic dermatitis, cholangiohepatitis as well as gizzard erosion.
Necrotic enteritis (NE) has been observed in several domestic and wild birds worldwide. Beside clinically manifested disease, subclinical infections may take place and are mostly accompanied with a reduction of performance. The most important source of infection in poultry appears to be contaminated feed, litter, water and the environment. The presence of C. perfringens in the intestinal tract or inoculation of the animals with high doses of C. perfringens, however, does generally not lead to the development of necrotic enteritis. One or several predisposing factors may be required to elicit clinical signs and lesions. It appears that some dysfunctions of the alimentary tract are a necessary predisposing cause of infection. Intestinal stasis, intestinal distension, coccidiosis, salmonellosis, crop mycosis and haemorrhagic enteritis (HE) may predispose the birds to infection. Factors predisposing the intestinal tract to overgrowth by clostridia organisms may also be the consumption of diets high in energy, protein and fish meal as well as the consumption of high fibre litter and wheat based diet.
On autopsy, dehydration is the most common finding. Breast muscles are dark red and gizzards are full of litter. Severe inflammation in the duodenum and jejunum is the most predominant finding, but in some instances the entire length of the intestinal tract is involved. The intestine is distended and contains dark, offensive fluid. The mucosa is covered with green or brown diphteroid membrane, which can be easily separated from the lining. Varying degrees of sloughing of the intestinal mucosa could also be observed. As the condition progresses, areas of necrosis can be recognised from outside of the intestine.
Control and treatment
Treatment with antibiotics such as penicillin, amoxicillin, ampicillin, erythromycin, dihydrostreptomycin and tetracyclin provided a satisfactory clinical response. The differences in susceptibility profiles between antimicrobials may reflect the varying use of these substances in poultry production. So it is useful to periodically monitor the antimicrobial resistance in different geographical areas to increase knowledge about the change in bacterial resistance, especially after the ban of antimicrobial growth promoters.
[Source: World Poultry magazine Vol 30 nr 5, 2014]