Combatting unseen parasites: A closer look at tapeworms and whipworms

Article sponsored by Merck Animal Health.

One of the most important topics on which veterinary professionals can educate clients is the importance of internal parasite protection. Most pet owners recognize the risks that more visible fleas and ticks pose. Fewer understand the health threats that internal parasites carry—to both pets and the humans who love them. Furthermore, many are unaware of how common parasitic infections are and how easily they spread.

The dilemma

As accessible and effective as these treatments are, data show two-thirds of dogs in the United States received no heartworm prevention during a 2013-2016 study period.¹ Despite recommendations for year-round parasite prevention by veterinarians, investigators found that the average dog receiving heartworm prevention receives 8.6 doses in a 12-month period.¹ Furthermore, between 2013 and 2016, the percentage of dogs receiving heartworm prevention decreased significantly, with only 35.69% of dogs receiving preventive products in 2016.¹ This offers a large opportunity for improved protection of our canine patients and their families.

Clients are quick to call the veterinary office when they notice changes in behavior, energy levels, or appetite. But it can be hard to address a problem they may never actually see. “It is out of sight, out of mind,” said Steve Milden, VMD, owner of Delaware Valley Veterinary Hospital in Mullica Hill, New Jersey.

Parasitic infections are hard to detect as adult worms are rarely seen and infectious eggs and larvae are microscopic. Additionally, many infected dogs are asymptomatic.² “I cannot tell you how many times I hear, ‘He doesn’t have parasites because I look at his stool and don’t see anything,’ Most infections we see are subclinical infections,” Dr. Milden said.

Even dogs displaying symptoms may go without a diagnosis because the common signs of internal parasites—vomiting, diarrhea, and weight loss—are nonspecific.² In this instance, ignorance is not bliss.

Tapeworms: More common than detected

Tapeworms are common internal parasites in dogs. According to the Companion Animal Parasite Council (CAPC), the reported prevalence of Dipylidium caninum in published studies varies from 4% to 60% in dogs.³ Why the disparity? The CAPC believes prevalence data generated by fecal flotation alone almost certainly underestimate the frequency of infection.³ This is because the eggs are heavy and do not readily float.³

Even in the presence of an infection, a given fecal sample may be negative for tapeworm proglottids or eggs.³ Studies of the prevalence of tapeworm infection in dogs and cats show a large disparity between the number of tapeworms diagnosed on necropsy and the number of these infections diagnosed by fecal flotation in the same animals.^4,5 In a 2017 study of shelter dogs in Oklahoma, D. caninum was detected in only 4.2% of dogs with fecal flotation.³ In contrast, 46.4% of dogs were diagnosed with D. caninum during necropsy.⁴

Dogs do not become infected by ingesting fertilized eggs in the environment, as is the case with most other internal parasites. Instead, tapeworm eggs are ingested by intermediate hosts, most commonly flea larvae.³ The egg becomes a cysticeroid within the flea larvae and stays in the flea body throughout maturation into an adult flea. The cysticeroid is the infectious stage to dogs and cats. Adult fleas can easily be ingested during regular grooming or in response to a flea bite. After ingestion by a vertebrate host, the cysticeroid develops into an adult worm. D. caninum eggs are found in proglottids, which are segments of the adult worm. These proglottids are passed with stool and are associated with irritation around the rectum.³

Although the visible proglottids can be alarming to pet owners, tapeworm infection is typically asymptomatic.⁶ However, some patients may present with signs of perianal discomfort.⁶

Key client education about tapeworms should include the following:^3,6

1. D. caninum is present worldwide. Tapeworm infection occurs most commonly through the ingestion of a flea, which makes flea control a critical part of parasite prevention.
2. Humans can become infected with D. caninum if they ingest an infected flea.

Whipworms: Hard to detect, harder to eliminate from the environment

Trichuris vulpis is another common gastrointestinal parasite of pet dogs. Much like tapeworms, whipworms are present in all 50 states, with areas such as West Virginia reporting a nearly 2% infection rate, or 1 in every 50 dogs, according to the CAPC 2021 prevalence map.⁷

Research has found whipworm infection in as many as 14.3% of shelter dogs sampled in the United States and 10% of dogs presented to veterinary teaching hospitals.⁸ But these are not the only populations at risk. Whipworms are not selective and are found worldwide, in kenneled, household, stray, and shelter dogs.⁹ “Living and working in the Northeast, we see frequent cases of whipworms,” Dr. Milden explained.

Dogs become infected with whipworms by swallowing infectious eggs in the environment such as soil.⁸ Adult whipworms primarily live in the cecum, where their feeding can cause dehydration, bloody diarrhea and weight loss in the host animal.⁸

The prepatent period for whipworm is rather long, at 74 to 90 days⁸, necessitating repeated fecal evaluations or empirical deworming for patients symptomatic for whipworm infection. Each female T. vulpis can produce more than 2000 eggs per day.⁸ “Unfortunately, whipworm eggs are shed periodically and are very heavy, so they are often missed on fecal flotations and analysis,” Dr. Milden added.

Once shed through an infected canine’s feces, infective whipworm eggs and require exposure to extreme conditions, such as extended periods of sunlight, to be killed.⁹Live eggs serve as a constant source of infection once mixed with soil because they are difficult to eliminate and continually expose dogs to reinfection.⁹

Key client education about whipworms should include the following:⁹

1. T. vulpis can cause bloody, mucoid diarrhea.
2. Eggs can remain infectious in the environment for years, necessitating year-round parasite prevention.

The solution

There are treatments readily available to protect beloved, furry family members from these hidden threats. “Since we started using a monthly product that controls intestinal parasites—including whipworms and tapeworms—we see less positive fecal analysis and much less clinical disease. New pets, either new puppies or clients new to our practice, get screened for parasites and educated on why we use the product we use,” Dr. Milden said.

SENTINEL® SPECTRUM® Chews (milbemycin oxime, lufenuron, and praziquantel) stand out in this category because of their ability to provide a spectrum of protection. A single monthly dose protects dogs from 6 types of parasites and stops flea eggs from hatching. Because young dogs are among the most susceptible to severe disease from parasitic infections, the chews are approved in puppies as young as 6 weeks.¹⁰ “Sentinel Spectrum is our primary, and typically only, recommended parasite preventive,” Dr. Milden explained.

So why aren’t all pets already protected? Pet owners trust the veterinary professionals who care for their pets, but it often takes multiple reminders about the importance of parasite protection before there is effective follow-through. Again, it often comes down to out of sight, out of mind.

By consistently using Sentinel products, the lufenuron prevents future generations of fleas, according to Dr, Milden.

Veterinary staff should be encouraged to start the conversation about parasite prevention early. Each new client and puppy visit should include an earnest discussion about the possibility of infection along with educational materials for pet owners to review at home. If a patient is not on preventives, follow up with clients at annual appointments and through email communications, mailed correspondence, and social media posts. There should be no question that preventives are the protection pets need.

IMPORTANT SAFETY INFORMATION:

SENTINEL® SPECTRUM® Chews (milbemycin oxime/lufenuron/praziquantel). Dogs should be tested for heartworm prior to use. Mild hypersensitivity reactions have been noted in some dogs carrying a high number of circulating microfilariae. Treatment with fewer than 6 monthly doses after the last exposure to mosquitoes may not provide complete heartworm prevention. See full prescribing information.

References

1. Drake J, Wiseman S. Increasing incidence of Dirofilaria immitis in dogs in USA with focus on the southeast region 2013-2016. Parasites Vectors. 2018;11(39). doi:10.1186/s13071-018-2631-0.
2. MacPete R. Intestinal parasites for dogs. Pet Health Network. Reviewed April 15, 2014. Accessed March 17, 2022. https://www.pethealthnetwork.com/dog-health/dog-diseases-conditions-a-z/intestinal-parasites-dogs.
3. Dipylidium caninum. Companion Animal Parasite Council. Updated November 1, 2016. Accessed October 31, 2021. https://capcvet.org/guidelines/dipylidium-caninum/.
4. Adolph C, Barnett S, Beall M, et al. Diagnostic strategies to reveal covert infections with intestinal helminths in dogs. Vet Parasitol. 2017;247(30):108-112. Doi.org/10.1016/j.vetpar.2017.10.002.
5. Little S, Adolph C, Downie K, Snider T, Reichard M. High prevalence of covert infection with gastrointestinal helminths in cats. J Am Anim Hosp Assoc. 2015;51(6):359-364. Doi.org/10.5326/JAAHA-MS-6221.
6. DPDx laboratory identification of parasites of public health concern: Dipylidium caninum.Centers for Disease Control and Prevention. Reviewed July 10, 2019. Accessed March 17, 2022. https://www.cdc.gov/dpdx/dipylidium/index.html#:~:text=Most%20infections%20with%20Dipylidium%20caninum,of%20the%20passage%20of%20proglottids.
7. Parasite prevalence maps. Companion Animal Parasite Council. 2021. Accessed November 22, 2021. capcvet.org/maps/#/2021/all-year/whipworm/dog/united-states.
8. Trichuris vulpis. Companion Animal Parasite Council. Updated July 28, 2020. Accessed September 28, 2021. https://capcvet.org/guidelines/trichuris-vulpis.
9. Raza A, Rand J, Qamar AG, Jabbar A, Kopp S. Gastrointestinal parasites in shelter dogs: occurrence, pathology, treatment and risk to shelter workers. Animals (Basel). 2018;8(7):108. doi:10.3390/ani8070108.
10. SENTINEL® SPECTRUM® CHEWS [prescribing information]. Madison, NJ: Merck Animal Health; 2020.