If you have horses or livestock, you’ll be very familiar with the concept of regularly testing for worm eggs. But for dogs, we don’t seem to do it so often… Why not? What are the pros and cons? Our vet blogger, Sarah-Jane Molier, investigates… 

Worm egg counts are a useful tool when used correctly. However, they cannot completely replace regular worming treatments. Let’s take a look at why that is!

What is a worm egg count? 

Worm counts involve analysing a stool sample from your dog, to detect any worm eggs or larvae present and to detect the number.  

The benefits of worm egg counts in dogs 

There are several benefits to performing worm egg counts in dogs, and they can be a useful tool for planning worm treatment and prevention for your dog. The benefits include: 

Targeted treatment 

If you are regularly monitoring your dog’s stool using high-quality worm egg count testing, you may avoid some unnecessary treatments for your dog. This is known as ‘targeted treatment’.  

However, there are some limitations to be aware of here, so your dog’s preventative health care will need to be planned using a risk/benefit analysis. Worm egg counts can certainly be useful for informing this analysis. 

Monitoring effectiveness of treatment 

Faecal (stool) worm egg counts are incredibly useful for assessing whether a particular treatment has worked. For example, say your dog had diarrhoea due to a parasite which has been treated, but the diarrhoea is persisting. Is the diarrhoea continuing because the treatment hasn’t eliminated the parasite yet, or is the diarrhoea now secondary to the resulting dysbiosis and residual inflammation? 

Re-infection is also common in some parasite infections, so regular worm egg counts can monitor for this, allowing you to treat your pet promptly.  

Reducing risk of resistance 

Vets are moving away from the blanket treatment of all pets with the same wormer at the same frequency, and moving towards more targeted treatments. This is part of a drive in the responsible use of antimicrobials (antibiotics) and anthelmintics (de-wormers) in both human and animal medicine. The aim is to reduce the risk of parasites becoming resistant to commonly used and important treatments. 

There are also wider spread environmental concerns around the overuse of flea and worm treatments. Worm egg counts can support responsible use, while also protecting animal and human health. 

Tracking local parasite prevalence 

On a wider scale, worm egg counts are useful for vets and veterinary parasitologists to track the local prevalence (how common they are) of parasites. This helps vets to use a risk-based approach, specific to their area.

The limitations of worm egg counts in dogs 

Nobody wants to overuse drugs, or to give their pet medicine that they don’t need. However, there are some important limitations to be aware of, should you choose faecal worm egg counts to replace regular worming. 

Sensitivity 

Unfortunately, faecal worm egg counts can miss parasites that don’t reliably shed in the faeces. For example, tapeworms only shed eggs intermittently, and they do so in heavy ‘gravid proglottids’ (egg-filled segments of tapeworm). This means they can be missed on faecal flotations. Lungworm is another example. Lungworm larvae are hard to detect, and multiple samples may need to be examined to reliably detect the larvae.  

Standard faecal egg counts have a sensitivity of around 60-70%. That means it will miss 30-40% of dogs that do in fact have a parasite burden. Lots of factors affect this: for example, the amount of sample (stool) provided, the testing technique and the fact that many parasites only shed intermittently. 

Intermittent shedding 

Many dog parasites don’t shed eggs / larvae continuously. This means that a single sample with a negative result does not guarantee that your dog is worm free. Your dog may still have a worm burden, but the stool was collected when the parasite wasn’t shedding.  

There is also the pre-patent period (the time between infection and when the parasite can be detected) to consider. If your dog was infected very recently, the parasite may not have reached the stage in their lifecycle where they would be shedding eggs or larvae yet. For example, whipworm won’t show up on an egg out until your dog has been infected for around 10-12 weeks, since it has a long prepatent period.  

This is important because some parasites can cause serious illness in the prepatent period, meaning it may be too late by the time the parasite is detected on faecal worm egg count. 

Zoonotic risk 

The main concern with some parasites, such as roundworms (Toxocara), is the fact that they are zoonotic. This means they can also infect humans, and particularly children or immunocompromised adults. If you only treat when an infection is detected, your dog would have already been shedding infectious eggs for some time, putting you and your family at risk. 

In fact, this zoonotic risk is one of the main differences driving how we approach parasite prevention in dogs compared with livestock. Treatment based on worm egg counts are routine horses and livestock, as there is no zoonotic risk associated with those parasites. Routine testing is therefore used to target treatments and reduce the risk of drug resistance (especially as drug resistance develops much faster in large animal herds). Farmers use worm egg counts to determine the animals shedding the most eggs, they can treat these and leave low-level shedders untreated.  

Technique 

Both the way a stool sample is handled (collected and stored by yourself and the lab) and the method of analysis (including the experience of the analyser) will affect how reliable the results are.

What the results of a worm egg count mean 

Good news, your dog’s stool sample came back negative! But what does that actually mean? Well, it means that the stool sample you submitted was negative. It does not necessarily guarantee that your dog is truly negative. It may miss: prepatent infections which are too early to detect, intermittent shedding, and parasites that don’t reliably shed in the stool. 

If the stool sample is positive for a parasite, your vet will advise the best course of treatment. They may also suggest follow up testing, to confirm treatment has worked. 

How to get the most out of worm egg counts 

Here are a few top tips for making the most of a worm egg count: 

  • Use a fresh sample and store it in a cool place 
  • Fill the sample pot to the max line to increase your chances of eggs/larvae being detected 
  • Use a pooled sample (a bit of stool from 3 days in a row)  
  • Use the right test! Which parasite you are most concerned about will determine which test is best. 
  • Only use reliable laboratories. It’s much better to arrange faecal testing through your vet. Not only will this guarantee the sample will be reliably tested using the right method for the parasite(s) of concern, but it also means a vet will go through the results with you. They can then prescribe treatment and advise on follow up testing as needed.  

Your vet will be happy to discuss worm egg counts with you, just make an appointment! 

Should you perform worm egg counts? 

Here’s the crunch – is it better to perform worm egg counts or to routinely de-worm? The answer is that a combination is probably ideal! If you live in a low-risk area, your dog isn’t a scavenger or raw fed, and you don’t have any children or immunocompromised adults in your household, then regular testing may be enough. However, this is not the case for most dogs! 

How often should you perform worm egg counts? 

The European Scientific Counsel Companion Animal Parasites (ESCCAP) set out guidelines based on risk. They recommend either treating or testing for nematodes and lungworm between 4 and 12 times a year, depending on your dog’s risk. They advise treating for tapeworms on a regular basis depending on risk, rather than testing. 

Lifestyle factors / risk 

So, what factors affect you/your dog’s risk? 

  • Lifestage: Puppies need regular worming due to high infection rates from their mothers 
  • Geography: how prevalent parasites are in your area 
  • Raw feeding increases their risk 
  • Does your dog come into contact with children, elderly or immunocompromised people? 
  • Lifestyle: does your dog eat slugs / snails or catch rabbits? Are there foxes in your garden or area? Does your dog frequently visit the park or mix with other dogs? 

Your vet will be able to advise you of your dog’s unique risk profile. 

Final Thoughts 

Worm egg counts are a useful tool, but they are not a perfect solution. A combination of regular testing and regular worming based on risk can work well. However, many pet owners prefer to de-worm on a risk-benefit analysis and save the cost of egg counts, and this is fine too! If you choose to use faecal egg counts to replace the need for regular de-worming, be prepared to test frequently (up to monthly depending on risk) to keep your pet, yourself and your family safe.  

Speak to your vet about tailoring a plan to fit your dog, your household, and your environment and lifestyle.