Infectious Diarrhoea

2016 | Disease | Mina Magelakis Scientific Services Australia

Diarrhoea is an increase in the frequency of defecation and or the lowering of faecal consistency. 

Pathogenesis

Diarrhoea that lasts less than 7 days that has an abrupt onset is very common in cats and dogs. Diarrhoea has many possible causes that disrupt the normal function of the intestinal wall in both the small and large intestine. Diarrhoea develops usually as a result of four main processes affecting digestion and absorption:

- Osmosis which is where foods that are not properly digested sit in the gut, ferment and draw water into the bowel leading to watery stools. This is common with sudden changes in diet, overconsumption of food and ingestion of spoiled foods.

- Secretory diarrhoea where the cells lining the gut are irritated and secrete large volumes of fluid into the bowel leading to watery bowel contents. An example of this would be infection with Salmonella bacteria.

- Increased permeability of the intestine is where water and other substances (e.g. electrolytes) can move more freely across the bowel wall due to damage to the intestinal lining. Excessive inflammation will cause this sort of change (e.g. hookworm infection, parvovirus infection).

- Increased motility where bowel movements are increased moving the gut contents through quicker. As they move through at a faster rate, there is not enough time for water to be absorbed well, resulting in a watery stool. This often occurs secondary to many disorders that cause diarrhoea. 

Kennel Management of Diarrhoea

Diarrhoea in dogs has many causes! The number of dogs affected in a kennel and the age of those showing signs is usually a good clue as to the cause for the diarrhoea. If predominantly young dogs are experiencing diarrhoea, it is likely due to an infectious agent (e.g. a virus, bacteria or parasite). Sometimes infections can occur with multiple infectious agents!
This is because younger animals have an immature immune system, may have experienced poor weaning practices or may not be up to date with vaccination. Diarrhoea affecting all the dogs in the kennels, especially where adult animals are also involved, is more likely to be due to inadequate sanitation practices in the kennels, stress or diet related (e.g. over-consumption of food or a sudden change in diet). 

Viral Diarrhoea

Viral infections are more common in young, unvaccinated puppies than adult dogs.
The coronavirus, rotavirus and parvovirus are the three main causes of viral diarrhoea in kennels.
Rotavirus can occur in dogs at any age but is more common in puppies less than 12 weeks old.
The virus is usually self-limiting and resolves within 5-7 days. Coronavirus also commonly occurs in puppies but they are usually over 10 weeks of age. The diarrhoea can last up to 12 days with soft stools persisting for a few weeks. These two viral infections destroy the cells of the intestinal lining reducing the ability of the gut to absorb nutrients and water. Because of the local destruction they cause, they can promote secondary infection with bacteria, parasites and even Parvovirus..
Canine parvovirusis more common in puppies (aged 6 weeks to 6 months) and unvaccinated adult dogs. Assuming that puppies receive adequate colostrum from the bitch, this should provide protection against parvovirus in the first few weeks of life. Parvovirus infection can be prevented with a modified live vaccination with the first booster given as early as 6 weeks of age.
The virus causes diarrhoea by damaging the cells in the intestine responsible for producing and maintaining a normal intestinal lining. As no new lining is produced, there is a loss of ability to absorb nutrients and water, and the lining may shed. This viral infection is severe and puppies present with vomiting, depression, fever, dehydration and foul smelling bloody diarrhoea.
Due to the extensive damage it causes to the intestinal lining and its direct effect on suppressing the immune system, these dogs can very quickly become septic and die. Treatment requires hospitalisation, intravenous fluid therapy and various medications to treat secondary bacterial infection and nausea.
Parvovirus is highly contagious and so affected animals should be isolated. The virus itself is very hardy, resistance to most detergents, lasting in the environment 6-12 months. 

Bacterial Diarrhoea

CampylobacterSalmonellaClostridia and E. coli are among the bacterial agents most commonly involved in diarrhoea in kennels. They have several common characteristics: - These bacteria are naturally present in the intestinal flora of dogs, but are not pathogenic as long as the balance of the intestinal flora is maintained and the animal possesses its full immune capacities. For example, a large number of epidemiological studies conducted in various countries on hundreds of healthy dogs living in kennels have shown that the shedding of campylobacter was regularly observed in more than 30% of animals, peaking around week 8. This healthy carriage rate is 43% in Australia, 32% in Switzerland, 26% in Spain, 37% in the USA, 29% in Sweden and 29% in Denmark.
Contaminated food that is slowly defrosted at ambient temperature (poultry, pork, beef, cow’s milk, carcasses and abattoir waste), faecal matter from infected animals or contaminated water are all possible sources of infection.

The ability of this group of bacteria to cause diarrhoea in mainly young puppies or adults usually occurs secondary to other conditions such as stress, concurrent disease (e.g. parvovirus infection)or unhygienic conditions. Sudden dietary changes can cause disturbances in the gut flora leading to overgrowth and infection by certain types of bacteria.
Some of these bacteria are zoonotic; meaning they can be transmitted to humans. Any dog presenting with diarrhoea, especially where bacterial causes are suspected, should be isolated and any humans in contact with the affected dogs should use personal protective equipment. 

Parasitic Diarrhoea

A large number of parasites can cause diarrhoea in a kennels environment, especially in young dogs.. Protozoan infections (e.g. Coccidiosis and Giardiasis)and nematode infections (e.g. roundworms, hookworms and whipworms) are the parasitic diseases most often responsible for diarrhoea in a kennel environment.

Giardia is a chronic intestinal infection with a protozoa. Infection is common in dogs and cats and is transmissible to humans. Transmission is usually from contamination of the environment with faeces from affected animals. The cysts that are shed into the environment are very hardy persisting in environments of high humidity and overcrowded kennels. The diarrhoea is chronic and intermittent, with foul smelling watery stools often with mucus. Treatment of affected animals and the environment using quarternary ammonium compounds is important to prevent re-infection and spread to other animals.
Coccidiosis, although not as common as Giardia, is caused by small protozoan organisms (e.g. Isospora) that infect puppies typically during weaning stress. They often cause severe diarrhoea, weight loss and dehydration. Sanitation is very important in kennels to prevent spread, specifically around ensuring faecal contamination of food and water sources is prevented.

Round worm infection, toxocariasis, is common in puppies. These worms are usually transmitted to the puppies in utero via the placenta or through the mammary gland when feeding from the bitch. The larvae can migrate to the lungs, liver and into the bloodstream from the gut. The larvae are passed in the faeces of the pups and are easily transmitted in a kennel environment between dogs. Young puppies affected don’t grow well and lose condition rapidly. They may also appear potbellied and have diarrhoea with mucus visible. Treatment and prevention of roundworms is based on an appropriate parasiticide protocol for all dogs in the kennel environment.
Roundworms are zoonotic and infections in humans can cause serious disease such as blindness due to larval migrans.
Whipworms and hookworms are also responsible for mild gastroenteritis in young puppies and adult dogs but are usually prevented with adequate anthelmintic treatment protocols. 

Diarrhoea caused by Diet

Excessive intake
The overconsumption of food overloads the gut and speeds up movement of gut contents. Undigested food ferments leading to undesirable changes in the intestinal flora and large volumes of fluid moving into the bowel, causing diarrhoea. Managing competition at feeding time to ensure no one dog consumes a large quantity of food is important.

Low food digestibility
Food of low quality, too rich in fermentable fibre, say, is likely to draw large volumes of fluid into the bowel and cause diarrhoea.

Transitions between diets
Dogs do not need variety in their diet and sudden dietary changes should be avoided. Where diet must be changed, a gradual transition is recommended to avoid gastrointestinal upsets. Gradually reducing the amount of old food and increasing the amount of new food is advised over a period of 7-10 days. A sudden change may cause significant disturbances to the intestinal flora causing diarrhoea.

Related Articles

Australian_Shepherd
Eclampsia