Pets, people and parasitic infections

Picking up after your dog is the right thing to do, and as a responsible pet owner, you know that this is what should be done, whether on a walk or in your own yard. But did you know that doing so also helps to protect other pets and people as well?

Dog waste is a potential source of parasitic infections that could cause direct harm to your dog as well as to other dogs and to people, with potentially serious consequences. These infections are caused by intestinal parasites that come in several forms. Two important varieties to be aware of are roundworms (nematodes) and tapeworms (cestodes).

ROUNDWORMS

Ascarids, also called roundworms, are most commonly found in young puppies (up to 6 months old) and occur very frequently. In fact, every puppy should be treated for “worms.” Roundworms may cause clinical signs such as diarrhoea, vomiting, lack of appetite and dehydration. If these symptoms occur together with an intestinal obstruction, they may even be fatal for a very young puppy.  You may observe a swelling of the puppy’s abdomen, taking on a “pot belly” appearance, and this is sometimes considered to be an indication of the presence of worms.

These parasites may cause no signs or less obvious signs in adult dogs, although lack of appetite, intermittent vomiting and lethargy are possible; however, these signs are common to several diseases.

How are these parasites transmitted?

Puppies can become infected with worms before they are born, with transmission of infective stages through the placenta. Not long after birth there can be further transmission through the mother’s milk or through contact with infective eggs in their environment. In adult dogs, infection comes from ingestion of infective worm eggs.

Once inside the dog, the worm eggs hatch and then the larvae go through a complex migration through the dog’s tissues, finally arriving in the intestinal tract to complete their cycle and become adults. This migration through tissues can cause injury to the dog.

The adult worms live in the intestine where they cause further harm while they compete with the dog’s digestive organs for nutrients. Diarrhoea, vomiting, and weight loss are some potential negative effects.

Risks to Human Health

Roundworm eggs are not infective at the time they are passed by dogs, but once in the environment they soon develop into an infective form. When people inadvertently ingest infective (embryonated) eggs of these roundworms, the developing worms cause a potentially serious health problem called Larval migrans, when the parasites try to migrate through tissues to complete their life cycle. These migrating larvae sometimes get lost and end up in other locations, causing injury and damage. In people, visceral larval migrans is the disease associated with mass migration of roundworm larvae through the human body, whereas ocular larval migrans refers to eye damage caused by aberrant migration of worm larvae through the eye.

TAPEWORMS

The tapeworms that infest dogs are often called cestodes because of the segmented appearance of their flat “ribbon-shaped” body.

The worm body is formed by segments, called proglottids in scientific terms, which are full of maturing eggs. These segments detach from the worm and are excreted with the dog’s faeces. The eggs then are typically picked up by another type of animal or insect and then migrate into an encysted form in tissues. This animal is called an intermediate host.

Later on, another dog becomes infested when it eats the encysted forms from the intermediate host.

The clinical signs of tapeworm infections are extremely variable and frequently, there are no signs of infection except when tapeworm segments may appear around the anus or in faeces. There are several types of cestodes, each with its own life cycle. One common type is spread by fleas, and this tapeworm is sometimes seen by pet owners as rice-sized segments on their dog or cat, particularly around the rear end of the animal.

Risks to Human Health

Some types of tapeworms can cause dangerous disease in people. Two of these are the dog tapeworm (Echinococcus granulosus) and the fox tapeworm (E. multilocularis), which can cause serious and potentially lethal disease in humans. The diseases in people are caused by the juvenile stages of these worms forming large cystic structures in human tissues. To control these dangerous infections, a person taking a dog to some countries must treat their dog to remove these parasites before entering that country. The adult forms of these tapeworms are small and do not shed motile segments.

The flea tapeworm mentioned above has the scientific name Dipylidium caninum and is a very common cestode infestation of dogs and cats. This tapeworm is transmitted through fleas. The dog becomes infested with adult worms after ingesting infected fleas while grooming. People, particularly children, can also become infected with the tapeworm after inadvertently swallowing an infected flea. In infected dogs and cats, mobile segments of this tapeworm may be seen on the faeces, around the anus, and in the pet’s bed – these look like rice grains when dry.

TREATMENT AND PREVENTION

It is important to start regular check-ups with your vet when your dog is a puppy. Puppies should be dewormed regularly from a couple of weeks after birth until the age of 6 months. The recommended frequency of worming dogs beyond this age may vary and should be determined by a veterinary assessment taking into account your pets age, lifestyle, household and potential risks in your area.

In the meantime, pet lovers should always act responsibly and help to reduce the transmission of these infections to other dogs and people by collecting and properly and promptly disposing of their dog’s waste. Keeping the environment clean helps to protect everyone’s health.