A BUG’S LIFE

EXTERNAL AND INTERNAL PARASITES OF THE CAT & DOG

Danielle J. Schaak, LVT, VTS (SAIM)

Diagnostic Imaging Department

Oakland Veterinary Referral Services

1400 S. Telegraph Rd

Bloomfield Hills, MI 48302

A parasite is a smaller organism that lives in or on and at the expense of a larger organism.

External Parasites:

Demodex is a cigar like external parasite that has 4 pairs of stubby legs. It can be a normal finding in small numbers in most dogs. It is when it becomes large numbers due to an immunodeficiency that it becomes a problem. Demodex is usually acquired during the first three days of life during nursing. A Demodex infection typically occurs in puppies 3-6 months of age and also due to an immunodeficiency. These patients have erythema, alopecia around eyes and mouth. The lesions they have are localized and not typically pruritic. These patients can be treated with Amitraz, Benzyl Benzoate, Rotenone, Ronnel, Cythioate. Chronic cases need to be treated with oral Ivermectin. With this treatment, results are typically seen within 4 months. An alternative to Ivermectin is Milbemycin Oxime orally for 12 months.

Sarcoptic mange is a zoonotic external parasite. It typically starts on a hairless area such as the ear pinna/elbows and then generalizes itself throughout the body. Causes follicular papules, erythema, pruritis as well as secondary bacterial infections. It can be very hard to diagnose; skin scrapings need to be very deep and can still be negative. Female mite burrows deep into epidermis to lay eggs which then take 21 days to hatch. Preferred treatment is clipping the fur followed by cleaning the sores with a Keratolytic Shampoo. Thereafter the patient will need to be treated with SQ injections of Ivermectin. Alternative to ivermectin is Amitraz baths.

Otodectes is commonly known as the ear mite and it affects ear canal and adjacent skin. Produces copious amounts of dark debris and cerumen from within the ear. Patients will violently shake their heads and scratch causing secondary aural hematomas. Diagnosis is simple with an ear swab. Preferred treatment is Ivermectin for 1-2 treatments 3 weeks apart. Also respond to pyrethrin and rotenone containing compounds. It is important to clean the ear prior to treatment.

Cheyletiella is also known as “Walking Dandruff”. It is more common in younger animals and tends to aggregates in larger numbers along the back. It can cause pruritis and scaling as well as localized lesions. It is usually diagnosed using the scotch tape technique – just pulling samples from the animal, adhering to the tape and looking microscopically. In cats, a fecal exam used to diagnose more often due to their grooming nature. Transmission is often accidental from host to host. Ideal treatment is Lindane Shampoo weekly for 6 weeks. Fipronil or Amitraz can also be used. It is also important to treat the environment with an organophosphate.

Lice are very species specific. They feed on the epidermal scales, feathers and sebaceous secretions of mammals and birds. Lice live their entire life on the hair of feather of the host, including the egg. They are more of a nuisance than a threat. Transmission from host to host is from close contact only. Lice are divided into two different categories - Mallophaga (chewing) and Anoplura (bloodsucking). Only a few or one species of a louse that belongs to a specific host. Treatment is usually 2 shampoos, sprays or dips containing Carbonyl at 1 week intervals.

There are more than 2000 species of Fleas, but dogs and cats are mostly bothered by Felis Canis. Paper chromatography is the easiest way to diagnose fleas. A life cycle of a flea can take anywhere from 2weeks to 2 years and is 100% dependent upon its environment. A flea can live for up to 2 months without a host, and up to 513 days on a host in an ideal condition. A flea does need an intermediate host to develop – Dipylidium caninum (tapeworm). Prevention is the absolute best treatment. Other treatments include Imidicloprid, Fipronil, S-Methoprene, Permethrin, Lufenuron and are applied topically. Many times environmental treatment is necessary as well.

All ticks are blood sucking parasites. Most ticks are vectors for microbial diseases and can cause injury to domestic animals and humans. Some ticks live in nests, burrows, buildings, and sleeping places of their hosts, while other ticks live in fields or scrubs and wait for their host to pass by. It is the saliva of the tick that transmits diseases such as Lymes Disease, Rocky Mountain Spotted Fever, Tick Paralysis, Colorado Tick Fever, and many more. It is important to remove the entire head and mouth when a tick is found. Once removed, it is best to send the tick out for analysis. Topical treatment is the best form of prevention, however there are newer oral preventions as well.

Internal Parasites

Roundworms is the largest and most familiar of all the intestinal parasites. There are three forms of roundworms - Toxacara canis, Toxascaris leonina, and Toxascaris cati. T. leonina is found in both canines and felines and is usually found in older animals. T. cati is specific to felines and is usually seen in the vomitus. Transplacental infection does not occur. T. canis is specific to canines. Transplacental infection does occur.

Ancylostoma caninum (large quantities of blood loss) and Uncinaria stenocephala (very little blood loss) are both known hookworms. Caused by ingestion or skin penetration of infective larvae. Infection varies in severity from asymptomatic to fatal. Reinfection a big problem so husbandry plays a large roll in controlling infection. Clinical signs precede the appearance off eggs in a fecal exam by 4 days. Pyrantel Pamoate, Dichlorvos, Mebendazole, Febantel, Fenbendazole, Milbemycin Oxime and Nitroscanate are all effective in treating hookworms. Treatment of hookworms should begin at 2 weeks of age and continue weekly for at least 3 months. Bitches can be treated with Fenbendazole at 50mg/kg/day from the 40th day of gestation to the 14th day of lactation.

Whipworms or Trichuris vulpis means “hair like tail”. Whipworms are very resistant to environment, so once again, reinfection is a problem. It can take up to three months for the egg to hatch after the larvae develops and then the life cycle thereafter can be very long. Most infestations can be symptomless, but severe infestations can cause alternating diarrhea with normal stool. Treatment needs to be re-administered at monthly intervals to destroy the worms due to a longer life cycle and to prevent recontamination. Treatments of choice are Fenbendazole or Drontal Plus.

Dipylidium caninum and Taenia are two different types of tapeworms, both requiring an intermediate host. Dipylidium needs a flea as an intermediate host, while Taenia needs a rodent such as a rabbit, rat or mouse as an intermediate host.

Taenia eggs are shed in the feces of the host, the rodents ingest the egg, the larvae infects the rodent, the rodent is then ingested by the host and the cycle then starts over again.

The larvae of the flea chews its way into the egg of the D. caninum egg and ingests the tapeworm. The flea larvae then metamorphosis’ and becomes an adult flea which is ingested by the host while grooming and will develop in the small intestine after ingestion. There have been 100+ reported cases of children getting D. caninum infection from flea ingestion. Treatment of tapeworm is usually Drontal or Drontal Plus, however, the fleas also need to be treated topically as well

Trophozoites and cysts are the two types of Giardia that we tend to see. Trophozoites are teardrop shaped, with 1 side pooched to form a sucking disc. Trophozoites can sometimes be seen in a direct smear, but usually turn into cysts before passing out with the feces and are not usually seen. Cysts can only be seen in a fecal float with zinc sulfate – sucrose or other medias tend to shrink or distort cysts beyond recognition. Cysts have 2 nuclei within 1 nucleus and a large endosome and are sometimes described as a tennis racket with eyes. Cysts are ingested from contaminated food or water and usually form within 1-2 weeks after contamination – however a dog can have diarrhea 5 days after exposure. Canines usually get treated with fenbendazole or metronidazole, whereas felines typically get treated with Metronidazole. Filtering and treatment of contaminated water and foods is also necessary.

There are many forms of Coccidia; however, Isospora, is the species that affects canines and felines. Ingested from infested soil or feces or from infected rodents. It is more common in younger animals, but not unheard of in adults. In an infected patient, stress can worsen coccidiosis. Host can have large amounts of watery diarrhea for several weeks and may precede the shedding of the cysts in the feces, making a diagnosis difficult. Typically treated with sulfonamides, but not always successful the first time

Heartworm Disease or Dirofilaria immitis is a serious and potentially fatal disease caused by a parasitic worm living in the arteries of the lungs of the right side of the heart of mammals. Heartworm is a form of a roundworm that has settled into the heart instead of the intestines. This parasite also needs an intermediate host to develop – the mosquito. The infected mosquito will bite the canine or feline transmitting the disease to them incidentally infecting them with a potentially fatal disease. Symptoms include coughing, exercise intolerance, abnormal lung auscultation, dyspnea, hepatomegaly, syncope, ascites, abnormal cardiac auscultation and death. The earliest a patient can be tested for heartworm antigen is at 5 months of age and for microfilaria at 6 ½ months of age, so ideal testing is at 7 months of age. Elisa testing for antigens is more sensitive than testing for microfilaria. Other diagnostics when heartworm is suspected might include thoracic radiographs and an echocardiogram, but are sometimes not as helpful unless it is a severe case.

Canine heartworm disease is usually treated with an adulticide first (Melarsomine Dihydrochloride). Second phase of treatment is usually an oral form (milbemycin) to kill any migrating microfilaria. All patients should be retested 6 months after treatment is completed. Another option for treatment is the surgical removal of the heartworms via fluoroscopy – only done is cases of heavy worm burdens that cause Caval Syndrome

Felines are more susceptible to heartworm disease, but more resistant at the same time – usually have a lighter worm burden (<6). Higher mortality rate than canines primarily due to the fact that there is no effective treatment for heartworm disease in felines and they tend to only exhibit transient clinical signs prior to death. First signs coincide with the arrival of adults in the pulmonary arteries 3-4 months after infection. Usually misdiagnosed as bronchitis or asthma due to the acute vascular and parenchymal inflammatory responses the body has. As worms mature, symptoms subside and eventually die off starting the 2nd stage of the disease causing pulmonary inflammation and thromboembolisms resulting in Acute Respiratory Distress Syndrome (ARDS). Caval Syndrome usually doesn’t happen in felines like in canines; however, 2 worms can result in a murmur as well. Symptoms include occasional GI upset, respiratory signs, neurological manifestations, anorexia, and lethargy. Ascites, hydrothorax, chylothorax, pneumothorax, ataxia, seizures, syncope, collapse, hemoptysis, and death are also symptoms, but are typically less frequent. Diagnostics should include both antibody and antigen serology testing which can be done anywhere between 5 ½ to 8 months post infection. Microfilaria are rarely present in felines. Radiographs and echocardiogram can also be key diagnostics in feline heartworm disease, unlike in canine heartworm disease. There is no treatment that has been proven to extend life. Prednisolone can be used for lung disease. Acute illnesses can be treated symptomatically and for shock. Only treatment is surgical removal of worms or monthly prevention.

The best and most effective treatment for parasites – internal or external – is preventative. Although not all parasites are proven to be fatal, even the parasites that seem to be less invasive to us can cause major illness to our loved companions. It is better to prevent illness than have to fight it off when it is too late.