PARASITES



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Choose a parasite:

Internal

External


A.)  Internal

  • Heartworm is an internal parasite that infects dogs and less commonly, cats. Transmission occurs via mosquitoes, which carry heartworm larvae (microfilariae) developing from the L1 to the infective L3 stage. These L3 larvae are deposited on the skin of an animal adjacent to a mosquito bite. Provided that there is adequate humidity to prevent evaporation of the droplet containing the larvae, they then swim through the bite and enter the skin, where they develop from an L3 to L5 stage. These L5 larvae then enters the bloodstream and localizes to the heart and pulmonary arteries, which can lead to arterial destruction and heart failure. Furthermore, clinical signs may include coughing, exercise intolerance, nose bleeds, pneumonia, fluid accumulation and more. However, the majority of dogs infected with heartworm in Ontario show no clinical signs at all until the disease has progressed a substantial amount. Fortunately, heartworm is both preventable (with yearly prophylactic medications) and treatable (if caught early enough).
  • The common tapeworm of dogs and cats is an internal parasite that is contracted when a pet consumes an infected flea, often while grooming their fur. The parasite then attaches to the intestine of the animal and grows a long tail composed of many segments. Within these, eggs develop and as the segments mature, they break off the back end of the growing tapeworm. These packets of eggs often become visible around the anus of an animal as rice-like particles that may move and cause your pet to rub their bum on the floor. The egg packets expelled from your pet are not immediately infective to the animal, since the next part of their life-cycle requires a flea. It is therefore imperative to to treat the concurrent flea infestation to avoid re-infection. Less commonly, other species of tapeworm can be contracted by consuming a prey animal, such as a rabbit or rodent infected with tapeworm larvae. The distinction between the two is useful when considering preventative measures. Although uncommon, it is possible for humans to get tapeworm by ingesting an infected flea or undercooked meat containing larvae. As well, cysts may form by ingesting certain tapeworm eggs.

  • Roundworms are a common internal parasite of both dogs and cats. Typically, puppies are infected in utero by their mother and therefore born with the parasites. Conversely, kittens often acquire the disease from their mother’s milk soon after birth. Additional modes of transmission include ingestion of eggs from the environment or ingestion of rodents harbouring infective larvae. While some species of roundworm are species specific, others may infect both dogs and cats. Clinical signs may include abdominal distension, abdominal pain, scant feces, coughing, a refusal to eat or nurse, and an inability to gain weight, or weight loss. Humans can also contract this parasite by inadvertently consuming their eggs, which leads to visceral larval migrans that typically causes eye problems and may even lead to blindness. For this reason, cats should be kept away from children’s sandboxes and care should be taken to thoroughly wash one’s hands.

  • Whipworms are internal intestinal parasites. Transmission occurs by ingestion of eggs from contaminated soil, which may persist there for months to years. Clinical signs with a heavy burden of worms includes bloody diarrhea in dogs. Conversely, cats are less commonly infected with a different species of whipworm and seldom display any symptoms. Fortunately, whipworms are not readily transmissible to humans.

  • Hookworms are blood-sucking internal parasites that latch onto the host’s intestinal wall via six sharp teeth. This occurs much more commonly in dogs then cats, with each animal having it’s own infective species of hookworm. Worms that escape the intestine can become dormant and encysted, waiting to periodically re-emerge, especially under the influence of pregnancy hormones. Eggs that are produced in the intestines pass via feces into the environment, where they mature into larvae capable of infecting a new host via in utero infection, by penetrating their skin, or by being ingested from the environment or the mother’s milk. Due to their limited blood volume, the risk to puppies is much greater then adult dogs and can frequently result in death if left untreated. As well, contaminated soil and improperly washed vegetables are a source of infection for humans, who typically develop cutaneous larval migrans or less commonly, an intestinal hookworm infection.
  • Coccidia (specifically, cystoisospora) are comprised of multiple species of microscopic, single-celled parasitic organisms that infect cats or dogs, but not both. However, ingestion by the non-host species does not result in death of the parasite and therefore environmental contamination can still result, despite the carrier animal remaining unaffected. The life-cycle of the parasite begins with soil contamination by oocysts passed in the feces, which mature and become infective. When a pet grooms contaminated dirt off of itself, or ingests a prey species that has inadvertently picked up the parasite, they acquire the infection. Oocysts then break open, releasing sporozoites that infect and destroy thousands of intestinal cells, leading to watery, bloody diarrhea. This fluid loss is especially concerning for small or young pets that may not have adequate reserves. Fortunately, while other species of coccidia, such as toxoplasma and cryptosporidium may infect humans, cystoisospora referred to here does not.

B.)  External

  • Fleas are external parasites that can live on dogs or cats and feed on their blood, causing itching and irritation. You should check your pets for fleas if you witness them biting, chewing, scratching or licking themselves excessively. To do so, part their fur and look for signs of fleas, or flea excrement known as flea dirt. You may also use a flea comb to brush some of the suspected flea dirt onto a light surface. Next, add some water and if the material liberates a red colour, this is evidence of digested blood and indicates a positive flea dirt identification. Fleas can cause a number of medical problems, including Flea Allergy Dermatitis (a reaction to the flea saliva), skin infections, tapeworm (if your pet ingests an infected flea), anemia, or even death in severe situations. Medication can be obtained from the veterinarian to help rid your pet of these pests! Additionally, your home and yard may may also need to be treated to prevent re-infestation.
  • Lice are a relatively rare external parasite and consist of those that either suck blood or chew skin as a food source. While both dogs and cats can become infested, no cross-transmission occurs between the two species, or humans due to the species-specific nature of lice. Contact with contaminated animals or objects can result in an infestation. Medications can be prescribed to treat the lice, and additional decontamination such as washing bedding may also be necessary.

  • Ear mites are a common external parasite that feed off of wax and skin oil within the ear. Transmission occurs freely between species and results from direct contact with an infected individual. If your pet’s ears appear to be irritated and/or contain a coffee-grind like substance, they may have a case of ear mites. Left untreated, this can progress to ear infections and skin disease. As well, it is often necessary to treat all the animals in a household to prevent reinfection.

  • The demodex mite (or red mite) is not to be confused with the sarcoptic scabei mite, which causes scabies. Demodex mites are external parasites that are normal inhabitants of canine hair follicles. These mites are transmitted from mother to offspring soon after birth, and dog and mite typically coexist peacefully. However, when immune suppression occurs, the mite may gain the upper hand and proliferate more extensively, giving rise to demodectic mange. This can manifest as a localized form, a more widespread generalized form with either juvenile or adult-onset, or demodectic pododermatitis, which is confined to the feet. Affected areas typically lack hair and may be red and inflamed, scaly and have a foul-odour if secondary infections are present. It is recommended that animals that suffer from generalized demodectic mange not be bred, as there is a genetic component to susceptibility. Where juvenile cases are concerned, an immature immune system is often to blame, and may therefore resolve with time and never reoccur. However, treatment is still recommended to facilitate recovery. Conversely, adult cases may have an underlying culprit impairing their immune system, and these occurrences therefore warrant closer investigation. (Note: Cats can also very rarely develop demodectic mange, but from a different strain of mite).

  • The sarcoptes scabei mite is not to be confused with the demodex mite, which can cause demodectic mange. The sarcoptes scabei mite is a very contagious external parasite that causes sarcoptic mange (or scabies) by burrowing through the skin, causing intense itching due to motion and an allergic reaction. Typically, hairless areas are affected first, including the abdomen, elbows and ear margins. Over time, this may progress to the rest of the body if left untreated. Transmission typically occurs by direct contact, although the mites may persist in the environment for up to 36 hours. As well, cats and humans are not optimal hosts for this mite and typically exhibit self-limiting infections, if anything. Scabies is difficult to diagnose and may present with clinical signs similar to environmental or food allergies.

  • Your dog’s lifestyle and geographic location determines their risk of exposure to ticks. These blood-sucking external parasites can cause tick paralysis, or diseases such as Rocky Mountain Spotted Fever or Lyme Disease by harbouring other infectious agents. To prevent this from occurring, residual insecticides can be used. As well, you should routinely check your pet for ticks to facilitate prompt removal. A tick twister (available at the Fergus Veterinary Hospital) can then be used to remove it, or an appointment can be made with the veterinarian if you require assistance. By following these guidelines, you decrease the likelihood of disease transmission from the tick to your pet.