Hookworms

Synopsis

CAPC Recommends

• CAPC recommends testing all dogs for hookworms by fecal flotation with centrifugation. Fecal tests for specific parasite antigens or PCR, which detects parasite DNA, are useful in identification of hookworms where few to no eggs and few adult worms are present, an infection with only young worms, or with single sex infections.

• Puppies should be tested more frequently than adult dogs. CAPC recommends testing for intestinal parasites, including hookworms, at least four times in the first year of life and at least two times per year in adults depending on patient health and lifestyle factors.

• Administer year-round broad-spectrum parasite control with efficacy against hookworms, and reduce exposure by timely removal of feces from the environment.

• As a parasite with zoonotic potential, control of hookworms is essential.

Species

Canine
Ancylostoma caninum
Ancylostoma braziliense
Uncinaria stenocephala

Overview of Life Cycle

• Adult hookworms live in the small intestine and shed eggs in feces and into the environment, where they larvate, hatch, and develop into infective third-stage larvae. This development occurs in approximately 2 to 9 days, depending on temperature and humidity.

• Dogs become infected with hookworms via ingestion of the third-stage larvae from a contaminated environment, larval penetration of the skin, and/or ingestion of other vertebrate hosts with infective larvae in their tissues. Dogs may also become infected by eating cockroaches that contain infective larvae.

• Transmammary transmission of larvae from the bitch to pups is an important route of infection for  A. caninum. In dogs  more than 3 months of age, some  A. caninum  will  migrate  through the lungs and enter somatic tissue, where the larvae become dormant, or arrested. Arrested development may also occur in the mucosa of the small intestine. These arrested larvae are activated after removal of adult worms from the intestine; activation also occurs during pregnancy, with the larvae accumulating in the mammary glands and  secreted in the milk.

• When infective larvae are ingested, some may penetrate the oral cavity and the gastro-intestinal tract mucosae and migrate as described; many of these larvae, however, remain in the alimentary tract and mature to adults in the small intestine.

• Larvae that infect other animals (paratenic/transport hosts) do not develop further in these hosts but become dormant (hypobiosis/arrested development) in various host tissues. When a dog ingests these larvae in animal tissues, the larvae travel to the small intestine, where they are released and mature into adult worms.

• Immature and adult worms attach to the mucosa of the small intestine, digest the tissue, inject anticoagulants, and suck blood. Worms may detach and move to new sites and reattach. Small bleeding ulcers form where the worms once fed.

• Adult worms may live for 4 to 24 months in the small intestine.

Stages

• Morulated hookworm eggs are passed in the feces of infected dogs; the most commonly seen species is  A. caninum  in the dog.

• Adult hookworms in the small intestine of infected dogs are attached to the intestinal villi by a large mouth cavity (buccal cavity).

• Male hookworms have a posterior copulatory bursa, and it is not uncommon to observe worms in copula in the small intestine.

• The anterior ends of both males and females are bent dorsally, giving them a "fishing hook" appearance.  A. caninum  have three pairs of teeth in the buccal cavity. Ancylostoma braziliense  has one pair of teeth (although some references mention a second, inconspicuous pair).  Uncinaria stenocephala  has cutting plates instead of teeth.

• Dog hookworms range in size from 10 to 20 mm by 0.4 to 0.5 mm.

• Eggs range in size from 55 to 90 μm by 30 to 55 μm, depending on the species.  Ancylostoma  spp. eggs are 55 to 75 μm by 34 to 47 μm;  U. stenocephala  eggs are 71 to 93 μm by 35 to 58 µm.

Ancylostoma caninum adults

Adult hookworms in the small intestine of infected dogs or cats are attached to the intestinal villi by a large mouth cavity (buccal cavity).

Ancylostoma spp. eggs canine 200X

Ancylostoma spp. eggs canine 400X

Ancylostoma sp. egg (arrow) and Cystoisospora spp. oocysts

Ancylostoma caninum anterior end

Disease

• All hookworms suck blood, but  A. caninum  is a voracious bloodsucker and can actually bleed a puppy to death. Disease in dogs caused by infection with  A. caninum  is most severe in young pups that are infected through nursing (the transmammary route) shortly after birth.
• Infected pups may present with pale mucus membranes and anemia, ill thrift, failure to gain weight, poor hair coat, dehydration, and dark, tarry diarrhea (melena). Puppies harboring many worms will develop an acute normocytic, normochromic anemia followed by hypochromic, microcytic anemia due to iron deficiency. Without immediate intervention, these animals may die of the infection. Those that survive may continue as "poor doers" with chronic anemia.
• Although some immunity to infection does develop, mature dogs may harbor small numbers of worms and contaminate the environment. If well-nourished and immunocompetent, these dogs will show few, if any, signs of disease. Adult dogs (particularly those that acquire many worms over a short period of time) may develop anemia, anorexia, emaciation, and weakness along with the characteristic dark, tarry diarrhea. These outcomes are more likely to occur in dogs that are stressed and malnourished.
• Respiratory disease and pneumonia may occur in puppies when large numbers of larvae migrate through the lungs. Respiratory signs may also be associated with hookworm-induced anemia.
• Ancylostoma caninum  is more pathogenic than  A. braziliense  because they are voracious bloodsuckers and consume much more blood than the latter.
• Penetration by larval hookworms occasionally causes a dermatitis with erythema, pruritus, and papules. These lesions are most commonly seen on the animal's feet, particularly in the interdigital spaces.  Ancylostoma caninum  and  A. braziliense  are most often the culprits

Prevalence

• Ancylostoma caninum  is a common parasite of dogs throughout the United States and are found in most tropical and subtropical environments.
• Both young and adult canine and feline hosts can harbor hookworms and pass eggs in their feces.
• In a survey conducted in 1996 using fecal samples collected from dogs across the United States, 19% of the fecal samples contained Ancylostoma  spp. eggs and 1.02% contained  Uncinaria  spp.  Ancylostoma  prevalence ranged from less than 5% in the west to 36% in the southeastern United States.
• The geographic distributions of  A. braziliense  and  U. stenocephala  are more limited.
  • In the United States,  A. braziliense  occurs in warm coastal areas; however, this parasite  is most common in tropical and subtropical regions of Central and South America and the Caribbean.
  • Uncinaria stenocephala, or the  northern carnivore hookworm, prefers colder climates and is most common in the northern United States, Canada, and Europe.
• The transfer of  A. caninum  larvae from mother to nursing offspring contributes to the high prevalence of infection in puppies, even in pets that are well cared for and routinely treated for intestinal parasites. Because somatic infection is common in adult dogs (even those on routine monthly intestinal parasite control), veterinarians should assume that essentially every nursing pup is at risk for hookworm anemia. Puppies should be routinely dewormed for hookworms. Deworming does not kill arrested larvae in the tissues (see Treatment ).
• Infection with hookworms occurs in all dogs, but infection rates are likely to be higher in pets kept outdoors.

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Host Associations and Transmission Between Hosts

• Dogs become infected with hookworms through ingestion of infective larvae from a contaminated environment, larval skin penetration, and/or ingestion of larvae in the tissues of vertebrate hosts (usually rodents).

• Puppies are infected with  A. caninum  when they ingest larvae while nursing. In adult dogs, Ancylostoma  spp. larvae become arrested in somatic tissues rather than completing the migration to the small intestine. During pregnancy, these arrested larvae are activated and accumulate in the mammary glands.

• In dogs that are cleared of their adult worm infections, the intestinal tract can be repopulated by preexisting, dormant larvae from the somatic tissues that periodically become activated and resume development.

Prepatent Period and Environmental Factors

• Ancylostoma caninum  usually becomes patent in 2 to 3 weeks, but puppies infected while nursing may shed eggs as early as 10 to 12 days after birth. Similar variations are seen in other hookworm species, but in general, the prepatent periods are 18 to 28 days for  A. tubaeforme  and 13 to 27 days for  A. braziliense  and  U. stenocephala.
• Most hookworm eggs larvate, hatch, and develop into infective third-stage larvae in the environment in approximately 2 to 9 days, depending on temperature and humidity. In general, the environmental stages thrive best away from direct sunlight in warm, moderately moist, aerated soils. Freezing kills Ancylostoma  spp. eggs, but  Uncinaria  eggs are hardier.
• Unlike ascarid eggs, hookworm larvae do not persist in the environment for years. Under optimal conditions, infective hookworm larvae can survive in the soil for a few months until their metabolic reserves are depleted. In addition, larvae usually are killed by freezing temperatures

Site of Infection and Pathogenesis

• Most hookworm species can penetrate the skin. As noted previously, occasionally the penetration of larval hookworms causes a dermatitis with erythema, pruritus, and papules. These lesions are most commonly seen on the pet's feet, particularly in the interdigital spaces.

• After skin penetration, hookworm larvae move via the lymphatics to the veins and lungs where they penetrate alveoli and migrate up the respiratory tree to the trachea. They are swallowed and return to the small intestine where they attach to the mucosa and mature into adults. Respiratory disease and pneumonia may occur in puppies when large numbers of larvae migrate through the lungs. Respiratory signs also may be associated with hookworm-induced anemia.

• Hookworms in the small intestine attach and secrete enzymes and anticoagulants to digest intestinal mucosa and facilitate bloodsucking. Hookworm platelet inhibitor decreases  platelet aggregation and adhesion. Intestinal villi are damaged and villus blunting occurs, resulting in malabsorption and diarrhea. Adult hookworms move to new feeding sites, leaving small bleeding ulcerations behind. Enteritis and diarrhea may develop during this intestinal phase.

• The major disease syndrome produced by hookworms is acute or chronic anemia from blood loss

Diagnosis

• CAPC recommends testing all dogs for hookworms by fecal flotation with centrifugation. Fecal tests for specific parasite antigens or PCR, which detects parasite DNA, are useful in identification of hookworms where few to no eggs and few adult worms are present, an infection with only young worms, or with single sex infections.
  

• Puppies should be tested more frequently than adult dogs. CAPC recommends testing for intestinal parasites, including hookworms, at least four times in the first year of life and at least two times per year in adults depending on patient health and lifestyle factors.
• Dogs of any age may have subclinical infections and show no signs of disease. However, when hookworm infections are allowed to persist, contamination of the environment with these potentially zoonotic parasites can occur.
• Ancylostoma caninum  and  A. tubaeforme  begin sucking blood before eggs are produced. In puppies infected by nursing their mother's milk, acute anemia and death may result before any eggs have passed in the feces.
• Fecal flotation with centrifugation
  • Diagnosis of patent hookworm infections via fecal flotation is straightforward. Hookworm eggs float readily in most flotation solutions.
  • Mix 1 to 5 g feces and 10 ml of flotation solution (ZnSO4 sp.gr. 1.18; sugar sp. gr. 1.25) and filter/strain into a 15-ml centrifuge tube.
  • Top off with flotation solution to form a slightly positive meniscus, add coverslip, and centrifuge for 5 minutes at 1500 to 2000 rpm.
  • Examine for characteristic eggs.
    • Eggs of  Ancylostoma  spp. can be differentiated from those of  Uncinaria stenocephala  by size (see images under Life Cycle) although the ranges overlap somewhat. Mixed infections sometimes occur.
      • Ancylostoma  spp.: 52-79µ x 28-58µ
      • Uncinaria stenocephala: 71-92µ x 35-58µ
• Fecal test for hookworm antigen
  • Commercial assays are available for detection of antigen produced by immature and adult hookworms in the lumen of the small intestine. Both male and female worms can be detected, and antigen production is not linked to egg production.
  • Diagnosis by detection of antigen allows identification of prepatent and single sex infections, supporting use of preventives and allowing earlier treatment.
  • Both centrifugal fecal flotation and fecal antigen tests have their strengths and weaknesses, however to ensure the widest breadth of detection of intestinal parasites in dogs, fecal tests for antigen should be combined with microscopic examination of feces for eggs.
• Fecal PCR tests for Hookworms
  • Nucleic acid is stable in the feces for 10 days at 4ºC.
  • Presence of DNA in feces is not linked to egg production.
  • May detect markers for resistance to certain medication(s).

Treatment

• In severely affected animals, anthelmintic treatment must be combined with supportive therapy to keep the animal alive until the drugs can kill the worms. In addition to keeping the patient warm, supportive treatment can include electrolyte and fluid therapy, iron supplements, a high-protein diet, and when clinically indicated, blood transfusions.
• Routine anthelmintic therapies do not kill arrested third-stage larvae in tissues.
  • Fenbendazole, milbemycin oxime, moxidectin, and pyrantel pamoate are approved for adult  A. caninum; pyrantel pamoate, fenbendazole, and moxidectin are approved for adult  U. stenocephala; and pyrantel pamoate is approved for adult  A. braziliense.
  • Moxidectin is approved for fourth-stage and young adult  A.caninum  and  U. stenocephala  in the intestine.

• Ancylostoma caninum:  The following products are approved for the treatment (and in some cases control*) of adult  A. caninum  infections in dogs:
  • Advantage Multi® Topical Solution for Dogs (imidacloprid + moxidectin)  (Elanco)*
  • Drontal® Plus Tablets (praziquantel/pyrantel pamoate/febantel) (Elanco)
  • Drontal® Plus Taste Tabs® (praziquantel/pyrantel pamoate/febantel) (Elanco)
  • HEARTGARD® Plus Chewables for Dogs (ivermectin/pyrantel)  (Boehringer Ingelheim)*
  • HeartShield™ Plus Flavored Chewables (ivermectin/pyrantel) (TruRx)*
  • Imectro™ (ivermectin, pyrantel pamoate and praziquantel) (Ceva)
  • Interceptor® Flavor Tabs® for Dogs & Cats (milbemycin oxime)(Elanco)*
  • Interceptor® Plus (milbemycin oxime/praziquantel)(Elanco)*
  • Iverhart Max® Chewable Tablets (ivermectin/pyrantel/praziquantel) (Virbac)*
  • IVERHART PLUS® Flavored Chewables (ivermectin/pyrantel) (Virbac)
  • MilbeGuard™ for Dogs (milbemycin oxime) (Ceva)
  • Panacur® Granules 22.2% (fenbendazole) (Intervet/Merck Animal Health)*
  • PetTrust™ Plus Chewable Tablets (ivermectin/pyrantel) (Sergeant's)
  • ProHeart® 6 (moxidectin) (Zoetis) *indicated for treatment of existing larval and adult hookworm infections
  • ProHeart® 12 (moxidectin) (Zoetis) *indicated for treatment of existing larval and adult hookworm infections
  • Sentinel® Flavor Tabs® (milbemycin oxime/lufenuron) (Merck Animal Health)*
  • Sentinel® Spectrum® Chewables (milbemycin oxime/ lufenuron/praziquantel) (Merck Animal Health)*
  • Simparica TRIO® (sarolaner, moxidectin and pyrantel): dogs (monthly oral) (Zoetis)
  • Trifexis® (milbemycin oxime/spinosad) (Elanco)*
  • Tri-Heart® Plus Chewable Tablets (ivermectin/pyrantel)  (Intervet/Merck Animal Health)*

• The following products are also approved for fourth-stage larvae (L4) and/or young adult  A. caninum  in dogs:
  • Advantage Multi® Topical Solution for Dogs (imidacloprid + moxidectin)  (Elanco)
  • ProHeart® 6 (moxidectin) (Zoetis) *indicated for treatment of existing larval and adult hookworm infections
  • ProHeart® 12 (moxidectin) (Zoetis) *indicated for treatment of existing larval and adult hookworm infections
  • Simparica TRIO® (sarolaner, moxidectin and pyrantel): dogs (monthly oral) (Zoetis)

• Ancylostoma braziliense: The following products are approved for the treatment (and in some cases control*) of adult  A. braziliense  infections in dogs:
  • HEARTGARD® Plus Chewables for Dogs (ivermectin/pyrantel)  (Boehringer Ingelheim)*
  • HeartShield™ Plus Flavored Chewables (ivermectin/pyrantel) (TruRx)*
  • Imectro™ (ivermectin, pyrantel pamoate and praziquantel) (Ceva)
  • Iverhart Max® Chewable Tablets (ivermectin/pyrantel/praziquantel) (Virbac)*
  • IVERHART PLUS® Flavored Chewables (ivermectin/pyrantel) (Virbac)
  • Tri-Heart® Plus Chewable Tablets (ivermectin/pyrantel)  (Intervet/Merck Animal Health)*

• Uncinaria stenocephala: The following products are approved for the treatment (and in some cases control*) of adult  U. stenocephala  infections in dogs:
  • Advantage Multi® Topical Solution for Dogs (imidacloprid + moxidectin)  (Elanco)*
  • Drontal® Plus Tablets (praziquantel/pyrantel pamoate/febantel) (Elanco)
  • Drontal® Plus Taste Tabs® (praziquantel/pyrantel pamoate/febantel) (Elanco)
  • HEARTGARD® Plus Chewables for Dogs (ivermectin/pyrantel)  (Boehringer Ingelheim)*
  • HeartShield™ Plus Flavored Chewables (ivermectin/pyrantel) (TruRx)*
  • Imectro™ (ivermectin, pyrantel pamoate and praziquantel) (Ceva)
  • Iverhart Max® Chewable Tablets (ivermectin/pyrantel/praziquantel) (Virbac)*
  • IVERHART PLUS® Flavored Chewables (ivermectin/pyrantel) (Virbac)
  • Panacur® Granules 22.2% (fenbendazole) (Intervet/Merck Animal Health)*
  • PetTrust™ Plus Chewable Tablets (ivermectin/pyrantel) (Sergeant's)
  • ProHeart® 6 (moxidectin) (Zoetis) *indicated for treatment of existing larval and adult hookworm infections
  • ProHeart® 12 (moxidectin) (Zoetis) *indicated for treatment of existing larval and adult hookworm infections
  • Simparica TRIO® (sarolaner, moxidectin and pyrantel): dogs (monthly oral) (Zoetis)
  • Tri-Heart® Plus Chewable Tablets (ivermectin/pyrantel)  (Intervet/Merck Animal Health)*

• The following products are also approved for fourth-stage larvae (L4) and/or young adult  U. stenocephala  in dogs:
  • Advantage Multi® Topical Solution for Dogs (imidacloprid + moxidectin)  (Elanco)
  • ProHeart® 6 (moxidectin) (Zoetis) *indicated for treatment of existing larval and adult hookworm infections
  • ProHeart® 12 (moxidectin) (Zoetis) *indicated for treatment of existing larval and adult hookworm infections
    

Suspected drug resistant hookworms

• Multi-anthelmintic drug resistant (MADR) Ancylostoma caninum infections have been observed and confirmed in several dog breeds around the USA, and are not limited to Greyhounds.
• Cases of suspected MADR hookworms should be assessed using a combination of anthelmintics, in conjunction with a fecal egg count reduction test (pre and post-treatment quantitative fecal analysis, 10-14 days apart). See reference Jimenez Castro & Kaplan (2020) for diagnostic algorithm
• Treatment may take months or years (depending on larval populations in tissues) and is also dependent upon environmental decontamination practices (e.g., removing feces immediately, avoiding dog parks when actively shedding ova) to minimize reinfection.
• Suggested treatments include one of the following combinations given monthly:
  • Febantel (25mg/kg) + Pyrantel pamoate (5mg/kg) + praziquantel (5mg/kg) + topical moxidectin (2.5mg/kg) given on the same day.
  • Fenbendazole (50mg/kg daily for 3 days) + pyrantel pamoate (5mg/kg) + topical moxidectin (2.5mg/kg) given on the same day (with fenbendazole continued for an additional 2 days).

• Worms that are not moxidectin-sensitive may not respond to the combination treatments. In those cases, extra-label use of emodepside may be considered. Dogs should be tested for heartworms (using an antigen test and modified Knott’s test) prior to being treated with off-label emodepside. Published studies show that, in vitro, emodepside has efficacy against many filarid life stages, which may result in adverse events in heartworm infected dogs.
• PCR may be available to help identify drug resistant hookworms in dogs.

Click here to view CAPC's Quick Product Reference Guide

Control and Prevention

• Puppies require more frequent anthelmintic administration than adult dogs because (1) they often are  serially reinfected via nursing and from the environment and (2) they often harbor migrating parasite larvae that later mature and commence laying eggs.

• Hookworm infections in puppies may cause serious illness or even death before a diagnosis is possible by fecal examination.

• In light of the hookworm prepatent periods, puppies and their dams  should be treated with appropriate anthelmintics when the young are 2, 4, 6, and 8 weeks of age. Puppies should be put on monthly preventives as soon as label recommendations allow. If puppies are not treated until 6 to 8 weeks of age or later, they should be put on a monthly preventive according to label recommendations, dewormed again in 2 weeks, and then maintained on appropriate monthly preventives thereafter.

• Beginning treatment when puppies are 2 weeks of age will help minimize environmental contamination.

• Pregnant bitches may be treated during pregnancy with daily fenbendazole (from the 40th day of gestation through the 14th day of lactation) or 2 to 4 times with a high dose of ivermectin to prevent transmammary transmission of hookworm larvae to the pups. Both protocols involve off-label use of anthelmintics.  High dose, off-label ivermectin should not be used in any dog with the MDR1 gene mutation.

• Efficacy of the initial dewormings, effectiveness of the monthly control product, and client compliance should be monitored by performing a fecal examination 2 to 4 times in the first year and 1 to 2 times annually thereafter, depending on the age of the animal and its prior history of infection.

• If unable to consistently administer a monthly preventive, then treat adult pets four times a year with a broad-spectrum anthelmintic with efficacy against internal parasites. This should coincide with appropriate fecal diagnostics.

• Preventing predation and scavenging activity by keeping cats indoors and dogs confined to a leash or a fenced yard will limit the opportunity for dogs to acquire infection with hookworms through ingestion of vertebrate hosts (usually rodents) or from an environment contaminated with feces from untreated animals.
  

• Prompt removal of feces from the yard or litter box will also help prevent hookworm eggs from hatching and larvae developing and dispersing into the environment.

• Enforcing leash laws and requiring owners to remove feces deposited by their pets can protect public areas from contamination with hookworm larvae.

Public Health Considerations

• Animal hookworms are well-documented zoonotic disease agents and are the most common cause of cutaneous larva migrans (CLM) in people. The larvae migrate in the skin, producing intensely pruritic, serpentine lesions. Usually these infections are self-limiting.  Ancylostoma braziliense  migrates more extensively in the skin than do the other hookworms.

• Humans are most likely to be infected with the hookworms of dogs and cats via direct skin penetration of infective larvae.  Ancylostoma caninum  can penetrate into deeper tissues and may arrest. On occasion,  A. caninum  can cause visceral larva migrans (VLM) when larvae migrate to the intestine and produce an eosinophilic enteritis. The worms do not mature to adults and no eggs are produced, but infected people may experience severe abdominal pain and eosinophilia.

• Most CLM and other hookworm-associated syndromes are diagnosed in the southeastern and Gulf Coast states. People at higher risk include  individuals in contact with larvae-contaminated soils such as electricians, plumbers, exterminators, and other workers who crawl beneath raised buildings; farmers and gardeners with close soil contact; sunbathers  reclining  on larvae-contaminated sand; and children playing  in contaminated areas.

• CLM is the most common travel-related skin infection in tourists to tropical areas.

• Early and regular deworming is essential in preventing contamination of the environment with hookworm eggs and larvae.

• Strict adherence to leash laws and prompt removal of feces from environments where pets defecate are key to protecting public areas from contamination; receptacles for the  disposal of feces should be provided.

• Children's sandboxes should be covered when not in use; outbreaks have occurred where larvae have developed to the infective stage in sandboxes and caused CLM in children.

• To avoid larval penetration, individuals should wear shoes and gloves when gardening.

• People whose occupations may  require contact with moist soil for extended periods of time should cover the contact area with a waterproof liner.

Selected References

• Elsemore DA, Geng J, Cote J, Hanna R, Lucio-Forster A, Bowman DD. 2017. Enzyme-linked immunosorbent assays for coproantigen detection of Ancylostoma caninum and Toxocara canis in dogs and Toxocara cati in cats. JVDI. 1-9.
• Adolph C, Barnett S, Beall M, Drake J, Elesmore D, Thomas J, Little S. 2017. Diagnostic strategies to reveal covert infections with intestinal helminths in dogs. Vet Par. 247:108-112.
• Lucio-Forster A, Liotta JL, Yaros JP, Briggs KR, Mohammed HO, Bowman DD. 2012. Morphological differentiation of eggs of  Ancylostoma caninum, Ancylostoma tubaeforme, and Ancylostoma braziliense  from dogs and cats in the United States. J Parasitol. 98(5):1041-4.
• Bowman DD, Montgomery SP, Zajac AM, Eberhard ML, Kazacos KR.  2010. Hookworms of dogs and cats as agents of cutaneous larva migrans. Trends Parasitol. 26(4):162-7.
• Little SE, Johnson EM, Lewis D, Jaklitsch RP, Payton ME, Blagburn BL, Bowman DD, Moroff S, Tams T, Rich L, Aucoin D. 2009. Prevalence of intestinal parasites in pet dogs in the United States. Vet Parasitol. 166(1-2):144-52.
• Lucio-Forster A, Bowman DD. 2011. Prevalence of fecal-borne parasites detected by centrifugal flotation in feline samples from two shelters in upstate New York.  J Feline Med Surg. 13(4):300-3.
• Jimenez Castro, PD and RM Kaplan. Persistent or suspected – resistant hookworm infections. Clinician’s Brief, August 2020; 61-68.
• Jimenez Castro, PD and RM Kaplan. Persistent hookworm infections in dogs. Clinician’s Brief, August 2020; 59.
• Venkatesan, A, et al., Molecular evidence of widespread benzimidazole drug resistance in Ancylostoma caninum from domestic dogs throughout the USA and discovery of a novel β-tubulin benzimidazole resistance mutation. PLOS Pathogens, 2023; 19(3).
• Jimenez Castro, PD, et al., Multiple anthelmintic drug resistance in hookworms (Ancylostoma caninum) in a Labrador breeding and training kennel in Georgia, USA. Journal of the American Veterinary Medical Association, 2022; 261(3).
• Zahner, H, et al., Filaricidal efficacy of anthelmintically active cyclodepsipeptides. International Journal for Parasitology, 2001; 31.