Flea Related Disease in Pet Animals

Our most important function as an animal hospital is for our staff members to understand the disease that fleas cause in pet animals, that we treat and care for. Fleas cause discomfort to the pet, are the cause of flea allergies and flea anemia, and can transmit Dipetalonema reconditum (heartworm look-a-like microfilaria), Hemobartonella, and tapeworms, as well as other diseases in pets.

Haemobartonella In Cats

Figure 7. Scanning electron micrograph of red blood cells infected with Haemobartonella.

Haemobartonella in cats causes a disease referred to as Feline Infectious Anemia or F.I.A. This illness is common in multi-cat households, which have large numbers of both cats and fleas. It is a protozoan parasite that attaches itself to the surface of the red blood cells. This parasite causes the red blood cells to appear abnormal to the body. The body then, in turn, destroys these cells causing the cat to be anemic. This picture shows a scanning electron microscope photo of red blood cells with these parasites embedded into their surface.


Flea Anemia in Pets

Fleas can be voracious bloodsuckers, with an unrelenting appetite that can kill a small dog or cat very quickly. The very young, very old, or debilitated animals are more prone to this type of assault. This is seen mostly with heavy flea infestations, occurring as the flea season begins with large numbers of new fleas emerging from cocoons. The animal may literally be overwhelmed by an acute attack of hundreds or thousands of fleas that create such an acute blood loss that the animal quickly becomes weak and unable to groom or move to a flea-free environment. An animal may also reside in an environment with a large flea burden, and the fleas over time, gradually cause severe anemia. This anemia develops because of chronic blood loss that exceeds the animal’s ability to replace the loss. In some pets, lack of appropriate response to anemia may be due to iron deficiency from the chronic blood loss. Others may have underlying disease or stress that prevents them from producing an appropriate response to the blood loss. The clinical signs of flea anemia in pets include pale mucous membranes (gums and sclera of the eyes), weakness, loss of appetite, and rapid shallow respiration. These animals have very little tolerance for stress and can literally die during blood collection or administration of a transfusion. Blood drawn from an anemic animal looks thin, almost translucent or Kool Aid® or wine-colored. The typical PCV is six to nine for an animal that is severely affected. Animals with moderate anemia (PCV = 12-20) are also commonly identified. These animals are most often seen for grooming or dipping and not specifically for the signs related to the anemia. The owner may think that the fleas, which have been difficult to control, need professional treatment. All animals presented with severe flea infestations need to be evaluated for anemia. Depending on the severity, the animal needs to be treated either with a transfusion or iron therapy and kept in the hospital until the environmental flea colony is controlled. These animals need to have the fleas on their body killed immediately either with a spray with quick “knockdown” or by shampooing. “Dipping” is avoided because anemic animals have a reduced ability to deal with pesticides.

Flea Allergies in Cats and Dogs

Allergies to the bite of a flea are very common in dogs and cats. The flea saliva is very antigenic (allergy causing) and can elicit a severe “itch-scratch” cycle. Flea allergies have a characteristic distribution on the pet with the caudal rump and head of the tail area being most severely affected. Cats will have allergic reaction distributed to the area around the neck as well as the rump area. The fleabite will cause the typical allergic reaction that leads the pet to chew or scratch at the area where the bite was. The resultant inflammatory reaction will cause the skin to become thicker. The flea cannot penetrate this same area on the skin causing the flea to move up the back more to a more cranial position to feed. In this way, a wedge of inflammation, hyperkeratosis, hyperpigmentation, and hair loss extends up the back from the tail area. This area is easily identified as being caused by flea allergies in dogs & cats. Many clients will however not agree with this diagnosis so caution is exercised when breaking this news to the client. Many clients will see their pet itching and chewing on the rump area but do not find any fleas upon examination. They may have other pets in the same environment on which they can find fleas. This misleads many clients into thinking that fleas are definitely not associated with the problem. Flea allergic pets will not have many fleas. It is these animals which are acutely sensitive to the bite of fleas that will excessively groom themselves. This excessive grooming and itch reaction will result in eradication of the fleas from the coat.


Dipylidium caninum is the name of the most common tapeworm found in dogs and cats. This tapeworm is transmitted by ingestion of a flea. This usually happens while the animal is grooming its coat with its mouth and inadvertently swallows an infected flea. The life cycle of the tapeworm involves the flea larva that ingests a tapeworm egg before forming its pupa or cocoon. When it emerges from its cocoon, it contains a tapeworm ready for ingestion by the final dog or cat host. Tapeworms “hatch” when the ingested flea is acted on by the gastric acid of the dog or cat. This new tapeworm is only a head of a tapeworm or “scolex”. The scolex of Dipylidium caninum has a ring of hooks around the top of its head. It uses these hooks to attach to the lining of the small intestine. It absorbs the digestive nutrients of the dog or cat host within the lumen of the small intestine and begins to grow in segments. Each segment produced is attached to the preceding segment in a chain, hence the name tapeworm. As more segments are produced the older segments mature. Each segment is capable of independent function and contains an intact digestive, respiratory, circulatory, and both male and female reproductive organs. As the segments mature, they each make fertile eggs, which are stored in packets of sixty to one hundred eggs. After the tapeworm segments are mature (the tapeworm may be many feet in length by this time), they will separate from the rest of the “worm”. They will then flow out of the pet with the stool. Their mission is to actually climb out of the rectum and deposit their eggs and egg packets on the skin and hair that surround the rectum. These worms segments can be seen as ¼ to ½ inch long, creamy, white “worms” moving in an “inchworm” fashion over the rectal area of the pet. These segments are depositing their eggs and afterwards will die and dry up to appear as a yellowish grain of rice. These may be seen stuck to the hairs of the rectal or perineal area or on furniture, bedding or the window ledge that the pet uses to look outdoors. These eggs are then ingested by developing flea larva and will be retained in these larvae during development to the adult flea. The adult flea will cause enough irritation to be chewed on by the infected pet. Pets with flea allergies groom more intensely and therefore will be more affected with tapeworms in a contaminated flea environment.

Unlike many tapeworm species, Dipylidium caninum does not necessarily cause serious pathology. There may be reduction in the absorption of B-vitamins, anal irritation, and other minor gastrointestinal disturbances. The primary reason for worming pets is that the pet owner is repulsed by the presence of the worm. It is not uncommon to receive emergency after-hours calls on the discovery of tapeworm segments on a pet by a novice pet owner. It is also not unusual for a pet owner to see a tapeworm segment, bring their pet in for fecal examination, and have a negative fecal test. Because the function of the worm segment is to leave the pet before laying its eggs, it is not unusual for a fecal examination to not show tapeworm eggs in the stool sample. These pets should be “wormed” based on the historical account of the owner.


As a member of the insect family, fleas are relatively easy to kill compared to roaches, bees or other insects with respect to their sensitivity to pesticides. Therefore, while killing fleas is easy, control of fleas is more difficult. Adult fleas, like other insects, are covered with a chitinous outer shell that is in turn covered with a waxy surface. This surface renders the flea impervious to water and therefore it is difficult to make a flea wet or to drown a flea. This defense helps protect a flea from water-soluble pesticides. This explains why alcohol is used in most flea sprays to help penetrate the chitinous skeleton of the flea. Pesticides need not necessarily be used to kill fleas because any detergent compound such as Ivory® soap or Joy® dishwashing detergent will kill fleas rapidly. These detergents reduce the surface tension of water making it flow into the fleas spiracles (breathing vents), thereby drowning the flea. This is a helpful when young puppies, kittens or exotic animals have fleas and the toxicity of the pesticide is of concern. The primary difference is the rate at which a flea will die, and not if the flea will die from either the detergent or pesticide.

Pesticides that have label claims of 100% effectiveness should be questioned. These products are tested by their ability to kill one hundred fleas in a dish in a certain time period. If the product kills all one hundred fleas, then the product is deemed 100% effective. This should not infer effectiveness on a pet or in the environment for flea control. Also, flea control products may tout that their effectiveness will have duration for some weeks or months (“will kill fleas for 17 weeks”). These products may have residual activity but they should not be depended on for flea control for this period of time. They may kill some fleas for this period of time, but they will not control fleas in high humidity areas of the country. Killing fleas in excess of their birth rate is the only way to control fleas. Few products have this ability without frequent repeated applications.

Flea Control

Fleas do not spend their entire life on a pet. Fleas only feed on them, jumping off with full bellies to breed in the yard or home. Because fleas spend a considerable portion of their time off the pet, flea control should begin at the ultimate source of the fleas – the outside or yard. Total flea control depends on controlling the environment (house and yard or “flea colony”) and the pet (food source), as well as breaking the flea life cycle. Each of these aspects is important. For example, it does little good to remove all the fleas from the pet, unless fleas are removed from the environment. Otherwise, fleas will simply jump back onto the pet and re-infest the animal, leaving you where you started.