How to choose coccidiosis diagnosis methods

A combination of traditional and modern methods will be the best way to correctly diagnose coccidiosis, allowing poultry producers to bring it under control.

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Male veterinarian working in laboratory. Vet doctor is examining sample at animal hospital. He is wearing uniform.
Male veterinarian working in laboratory. Vet doctor is examining sample at animal hospital. He is wearing uniform.
Laboratory staff must be capable of properly processing samples and interpreting the results if a correct diagnosis is to be obtained. Morsa Images | iStock.com

Technological advances are now providing alternative methods to identify and measure coccidiosis in flocks, and both new and traditional methods should be considered for diagnosing and measuring the Eimeria species in a flock.

Start with traditional diagnostic methods

Significant information can be gained from traditional diagnostic methods of oocyst counts and lesion scores. Oocyst counting involves microscopic evaluation of the number and developmental stage of oocysts in feces or litter.

For fecal counts, the oocysts must be separated from as much feces and debris as possible to obtain accurate readings. Reliable oocyst counts from litter require the sampling of multiple locations throughout the facility.   

Optimizing oocyst counts

To optimize oocyst counts:

  • Ensure personnel are appropriately trained. In particular, train personnel using pure parasite suspension obtained from a laboratory prior to having them evaluate mixed cultures. 
  • Take into account that more prolific Eimeria species may mask the presence of less prolific species. Careful evaluation of multiple slides may be required to obtain accurate readings. 
  • Use only samples in good condition. Samples should be fresh, preferably no more than seven days should have elapsed since collection. They should be refrigerated to prohibit maturation and atypical forms.

Lesion scoring involves the identification of Eimeria species based on the location and appearance of gross lesions in the intestines. As examples, lesions produced by E. acervulina and E. mivati occur primarily in the duodenal loop and the upper part of the jejunum, while lesions of E. tenella are found mostly in the ceca.  

Dead ChickCoccidiosis is probably the most economically important disease of poultry worldwide, making its control essential. Kingarion| iStock.com

 

Optimizing lesion scoring

To optimize lesion scoring:

  • Ensure staff are appropriately trained and experienced in lesion scoring and the evaluation of the mixed species infections seen in the field.
  • For consistency, use the same individuals to conduct all lesion scoring. Alternatively, pool the results of multiple individuals.
  • Compare results with historical data.
  • When available, use programs provided by the pharmaceutical industry.
  • Conduct lesion scoring multiple times throughout the year.  
  • Ensure a good light source, such as a surgical lamp or direct sunlight, is available.
  • A microscope should be available to examine smear preparations for parasites if lesions are difficult to identify. 

These traditional methods are labor intensive and, therefore, costly. Although oocyst count is a valuable tool, the number of oocysts does not, necessarily, correlate to disease state. While lesion scoring is considered to have a stronger correlation to disease state, it is still limited since not all Eimeria species, for example E. mitis, cause clearly visible lesions.

Consider PCR technology to improve capabilities

DNA-based methods, such as PCR, overcome some of traditional methods’ limitations. Using PCR methods, more samples can be analyzed in less time, with increasing sensitivity and single-step quantitation.  

Basic PCR can differentiate between the primary Eimeria species. Advances in PCR technology include:

  • Development of alternative primers to provide greater Eimeria species delineation.
  • Optimization of methods to obtain and purify DNA. This is critical since feces contains substances that inhibit the action of the enzyme required for the amplification of the DNA. 
  • Use of internal controls to reduce false negative results caused by the inhibitor.
  • Accurate identification and quantitation of each Eimeria species present, even in samples with multiple species.    

Continue to explore alternative methods

Coccimorph is a computational software that uses oocyst morphology to identify different Eimeria species and is an accessible and low-cost addition to traditional oocyst counting. On the downside, it only measures sporulated oocysts, which limits the technique’s use in litter samples.

Loop-mediated Isothermal amplification (LAMP) is an alternative molecular approach that uses isothermal enzymes and intercalating dyes to eliminate the need for a thermocycler and electrophoresis, equipment needed for PCR methods. Additional research is required before LAMP can be used for commercial purposes, however.   

Improvements in technology now allow for a mini-mass spectrophotometer and associated equipment to be placed on a cart and used at a poultry facility. Using this equipment, researchers have developed a model to differentiate the fecal metabolic profiles between healthy and E. tenella infected birds. Once the technique is refined to identify multiple Eimeria species, it could provide faster, on-site coccidiosis diagnosis. 

Ensure lab is qualified and capable

To obtain accurate results, the laboratory must be adequately staffed with qualified personnel capable of processing samples and interpreting the results. Samples must be processed in a consistent manner so that valid, repeatable and accurate results are obtained.  

Consider multiple factors when diagnosing 

A coccidiosis infection is a complex disease state. The best diagnosis is obtained using a combination of traditional methods and modern methods, as well as evaluating live animals for clinical signs and growth parameters. Consider all factors prior to making treatment decisions.

Finally, remember that coccidiosis as a disease will never be eradicated. The objective will always be to appropriately diagnose, prevent and treat coccidiosis in order to reduce its economic burden and the welfare issues created by the disease.   


How to proactively control coccidiosis in ABF poultry


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