In adult swine, the disease is very mild and mortalities are rare. The primary signs are a watery diarrhoea and mild systemic signs such as pyrexia, anorexia and lethargy.

Diagnosis is via immunofluorescence or immunohistochemistry, and ELISA can detect antigen or antibodies.

Porcine epidemic diarrhoea is a condition caused by the porcine epidemic diarrhea virus that leads to severe gastrointestinal disease in pigs.

It is closely related to the agent responsible for transmissible gastroenteritis in pigs. Piglets are most susceptible to the disease, as are young adults during periods of stress. Transmission is via the faecal-oral route.

Rotavirus gastroenteritis is a mild to severe disease characterised by vomiting, watery diarrhoea, and low-grade fever. Once a child is infected by the virus, there is an incubation period of about two days before symptoms appear. Symptoms often start with vomiting followed by four to eight days of profuse diarrhoea. Dehydration is more common in rotavirus infection than in most of those caused by bacterial pathogens, and is the most common cause of death related to rotavirus infection.

Rotavirus A infections can occur throughout life: the first usually produces symptoms, but subsequent infections are typically mild or asymptomatic, as the immune system provides some protection. Consequently, symptomatic infection rates are highest in children under two years of age and decrease progressively towards 45 years of age. Infection in newborn children, although common, is often associated with mild or asymptomatic disease; the most severe symptoms tend to occur in children six months to two years of age, the elderly, and those with compromised or absent immune system functions. Due to immunity acquired in childhood, most adults are not susceptible to rotavirus; gastroenteritis in adults usually has a cause other than rotavirus, but asymptomatic infections in adults may maintain the transmission of infection in the community.

Rotavirus enteritis is the most common cause of severe diarrhoea among infants and young children. It is caused by Rotavirus, a genus of double-stranded RNA virus in the family "Reoviridae". By the age of five, nearly every child in the world has been infected with rotavirus at least once. However, with each infection, immunity develops, and subsequent infections are less severe; adults are rarely affected. There are five species of this virus, referred to as A, B, C, D, and E. Rotavirus A, the most common, causes more than 90% of infections in humans.

The virus is transmitted by the faecal-oral route. It infects and damages the cells that line the small intestine and causes gastroenteritis (which is often called "stomach flu" despite having no relation to influenza). Although rotavirus was discovered in 1973 and accounts for up to 50% of hospitalisations for severe diarrhoea in infants and children, its importance is still not widely known within the public health community, particularly in developing countries. In addition to its impact on human health, rotavirus also infects animals, and is a pathogen of livestock.

Rotavirus is usually an easily managed disease of childhood, but worldwide nearly 500,000 children under five years of age still die from rotavirus infection each year and almost two million more become severely ill. In the United States, before initiation of the rotavirus vaccination programme, rotavirus caused about 2.7 million cases of severe gastroenteritis in children, almost 60,000 hospitalisations, and around 37 deaths each year. Public health campaigns to combat rotavirus focus on providing oral rehydration therapy for infected children and vaccination to prevent the disease. The incidence and severity of rotavirus infections has declined significantly in countries that have added rotavirus vaccine to their routine childhood immunisation policies.

The illness usually starts with an attack of acute diarrhoea, fever and malaise following which, after a variable period, the patient settles into the chronic phase of diarrhoea, steatorrhoea, weight loss, anorexia, malaise, and nutritional deficiencies.

The symptoms of tropical sprue are:

- Diarrhoea

- Steatorrhoea or fatty stool (often foul-smelling and whitish in colour)

- Indigestion

- Cramps

- Weight loss and malnutrition

- Fatigue

Left untreated, nutrient and vitamin deficiencies may develop in patients with tropical sprue. These deficiencies may have these symptoms:

- Vitamin A deficiency: hyperkeratosis or skin scales

- Vitamin B and folic acid deficiencies: anaemia

- Vitamin D and calcium deficiencies: spasm, bone pain, numbness, and tingling sensation

- Vitamin K deficiency: bruises

Barcoo fever is an illness once common in the Australian outback that is now virtually unknown. It was characterised by nausea and vomiting exacerbated by the sight or smell of food and, unlike the usual gastro-intestinal infections, by constipation rather than diarrhoea. Fever and myalgia were also symptoms. Severe cases developed inanition and even death. It was seen in travelers in the outback rather than in cities or towns, but occasionally entire settlements were affected, such as occurred in Toowoomba in 1903. The aboriginal population knew to avoid the ailment by not drinking from certain water sources and by taking water from soaks or pits dug in the dry sandy bed of a stream.

It is postulated that the disease may be due to ingestion of cyanobacterial (blue-green algal) toxins, in particular cylindrospermopsin, a toxin from "Cylindrospermopsis raciborskii" and other cyanobacteria, which is a hepatotoxin. The symptoms of the disease are consistent with a hepatitis or liver disorder, and "Cylindrospermopsis" is known to be widespread in inland Australian water sources. The toxin is not destroyed by boiling and, although it would flavor water, this flavor would be masked by tea, the common beverage in the Australian bush. Provision of safe drinking water sources in Australia, with the development of bores and covered tanks to collect rainwater, explain the demise of a once-common illness.

Tropical sprue is a malabsorption disease commonly found in tropical regions, marked with abnormal flattening of the villi and inflammation of the lining of the small intestine.

It differs significantly from coeliac sprue. It appears to be a more severe form of environmental enteropathy.

In humans, the virus can cause several syndromes. Usually, sufferers have either no symptoms or only a mild illness with fever, headache, muscle pains, and liver abnormalities. In a small percentage of cases (< 2%), the illness can progress to hemorrhagic fever syndrome, meningoencephalitis (inflammation of the brain and tissues lining the brain), or affect the eye. Patients who become ill usually experience fever, generalised weakness, back pain, dizziness, and weight loss at the onset of the illness. Typically, people recover within two to seven days after onset.

About 1% of people with the disease die of it. In livestock, the fatality level is significantly higher. Pregnant livestock infected with RVF abort virtually 100% of foetuses. An epizootic (animal disease epidemic) of RVF is usually first indicated by a wave of unexplained abortions.

Other signs in livestock include vomiting and diarrhoea, respiratory disease, fever, lethargy, anorexia and sudden death in young animals.

Rotavirus is the most common cause of diarrhoeal disease among infants and young children. It is a genus of double-stranded RNA viruses in the family "Reoviridae". Nearly every child in the world is infected with rotavirus at least once by the age of five. Immunity develops with each infection, so subsequent infections are less severe; adults are rarely affected. There are eight species of this virus, referred to as A, B, C, D, E, F, G and H. "Rotavirus A", the most common species, causes more than 90% of rotavirus infections in humans.

The virus is transmitted by the faecal-oral route. It infects and damages the cells that line the small intestine and causes gastroenteritis (which is often called "stomach flu" despite having no relation to influenza). Although rotavirus was discovered in 1973 by Ruth Bishop and her colleagues by electron micrograph images and accounts for approximately one third of hospitalisations for severe diarrhoea in infants and children, its importance has historically been underestimated within the public health community, particularly in developing countries. In addition to its impact on human health, rotavirus also infects animals, and is a pathogen of livestock.

Rotavirus is usually an easily managed disease of childhood, but in 2013, rotavirus caused 37 percent of deaths of children from diarrhoea and 215,000 deaths worldwide, and almost two million more become severely ill. Most of these deaths occurred in developing countries. In the United States, before initiation of the rotavirus vaccination programme, rotavirus caused about 2.7 million cases of severe gastroenteritis in children, almost 60,000 hospitalisations, and around 37 deaths each year. Following rotavirus vaccine introduction in the United States, hospitalisation rates have fallen significantly. Public health campaigns to combat rotavirus focus on providing oral rehydration therapy for infected children and vaccination to prevent the disease. The incidence and severity of rotavirus infections has declined significantly in countries that have added rotavirus vaccine to their routine childhood immunisation policies.

In 1979 an outbreak of hepatoenteritis, also known as the Palm Island mystery disease, was reported and described a hepatitis-like illness (associated in many cases with dehydration and bloody diarrhoea) in 148 people (138 children and 10 adults) of Aboriginal and Torres Strait Islander descent in Palm Island, Queensland.

Symptoms may include fever and headache, but the distinguishing characteristic of this disease is attacks of severe pain in the lower chest, often on one side. The slightest movement of the rib cage causes a sharp increase of pain, which makes it very difficult to breathe, and an attack is therefore quite a frightening experience, although it generally passes off before any actual harm occurs. The attacks are unpredictable and strike "out of the blue" with a feeling like an iron grip around the rib cage. The colloquial names for the disease, such as 'The Devil's grip' (see also "other names" below) reflect this symptom.

Coccidiosis is a parasitic disease of the intestinal tract of animals caused by coccidian protozoa. The disease spreads from one animal to another by contact with infected feces or ingestion of infected tissue. Diarrhea, which may become bloody in severe cases, is the primary symptom. Most animals infected with coccidia are asymptomatic, but young or immunocompromised animals may suffer severe symptoms and death.

While coccidia can infect a wide variety of animals, including humans, birds, and livestock, they are usually species-specific. One well-known exception is toxoplasmosis caused by "Toxoplasma gondii".

Humans may first encounter coccidia when they acquire a puppy or kitten that is infected. Other than "T. gondii", the infectious organisms are canine and feline-specific and are not contagious to humans, unlike the zoonotic diseases.

Nephropathia epidemica ("NE" or epidemic nephropathy) is a type of viral haemorrhagic fever with renal syndrome (HFRS) caused by the Puumala virus. The incubation period is three weeks. Nephropathia epidemica has a sudden onset with fever, abdominal pain, headache, back pain and gastrointestinal symptoms. More severe symptoms include internal hemorrhaging. Although fatal in a small percentage of cases, nephropathia epidemica is generally milder than the HFRS that is caused by hantaviruses in other parts of the world. The bank vole is the reservoir for the virus, which humans contract through inhalation of aerosolised vole droppings.

The majority of infected individuals are asymptomatic or develop only mild symptoms, and the disease is not known to spread from human to human.

This infection is known as "sorkfeber" in Swedish and "myyräkuume" in Finnish (vole fever). In Norway, it is called "musepest" (mouse plague).

Rift Valley fever (RVF) is a viral disease that can cause mild to severe symptoms. The mild symptoms may include: fever, muscle pains, and headaches which often last for up to a week. The severe symptoms may include: loss of sight beginning three weeks after the infection, infections of the brain causing severe headaches and confusion, and bleeding together with liver problems which may occur within the first few days. Those who have bleeding have a chance of death as high as 50%.

The disease is caused by the RVF virus, which is of the "Phlebovirus" type. It is spread by either touching infected animal blood, breathing in the air around an infected animal being butchered, drinking raw milk from an infected animal, or the bite of infected mosquitoes. Animals such as cows, sheep, goats, and camels may be affected. In these animals it is spread mostly by mosquitoes. It does not appear that one person can infect another person. The disease is diagnosed by finding antibodies against the virus or the virus itself in the blood.

Prevention of the disease in humans is accomplished by vaccinating animals against the disease. This must be done before an outbreak occurs because if it is done during an outbreak it may worsen the situation. Stopping the movement of animals during an outbreak may also be useful, as may decreasing mosquito numbers and avoiding their bites. There is a human vaccine; however, as of 2010 it is not widely available. There is no specific treatment and medical efforts are supportive.

Outbreaks of the disease have only occurred in Africa and Arabia. Outbreaks usually occur during periods of increased rain which increase the number of mosquitoes. The disease was first reported among livestock in Rift Valley of Kenya in the early 1900s, and the virus was first isolated in 1931.

Porcine enzootic pneumonia is caused by "Mycoplasma hyopneumoniae" and describes an important respiratory disease of pigs.

It is part of the Porcine Respiratory Disease Complex along with Swine Influenza, PRRS and Porcine circovirus 2, and even though on its own it is quite a mild disease, it predisposes to secondary infections with organisms such as "Pasteurella multocida".

Clinical signs are most commonly seen in pigs over 8 weeks of age, and the disease occurs worldwide. Transmission is horizontal and vertical from sows.

Rotaviral enteritis is a mild to severe disease characterised by nausea, vomiting, watery diarrhoea and low-grade fever. Once a child is infected by the virus, there is an incubation period of about two days before symptoms appear. The period of illness is acute. Symptoms often start with vomiting followed by four to eight days of profuse diarrhoea. Dehydration is more common in rotavirus infection than in most of those caused by bacterial pathogens, and is the most common cause of death related to rotavirus infection.

Rotavirus A infections can occur throughout life: the first usually produces symptoms, but subsequent infections are typically mild or asymptomatic, as the immune system provides some protection. Consequently, symptomatic infection rates are highest in children under two years of age and decrease progressively towards 45 years of age. The most severe symptoms tend to occur in children six months to two years of age, the elderly, and those with immunodeficiency. Due to immunity acquired in childhood, most adults are not susceptible to rotavirus; gastroenteritis in adults usually has a cause other than rotavirus, but asymptomatic infections in adults may maintain the transmission of infection in the community. There is some to evidence to suggest blood group secretor status and the predominant bacteria in the gut can impact on the susceptibility to infection by rotavirus.

Pigs usually cough and may show more severe respiratory signs if secondary bacteria have invaded. This may lead to signs of pneumonia and systemic involvement.

Diagnosis relies on culture and isolation of the bacteria but this can be challenging.

PCR, ELISA, fluorescent antibody testing and post-mortem findings all help in making the diagnosis.

Symptoms of hepatoenteritis included diarrhoea, vomiting attacks, loss of balance and disorientation.

The perinatal effects of cyanobacteria contamination of drinking water include prematurity, low birth weight and congenital defects detected at birth. In 1996 there were 63 deaths attributed to drinking water contamination in Caruaru, Brazil.

The illness lasts about a week and is rarely fatal. Treatment includes the administration of nonsteroidal anti-inflammatory agents or the application of heat to the affected muscles. Relapses during the weeks following the initial episode are a characteristic feature of this disease.

The acute form of the disease is manifested by lethargy, loss of appetite, vomiting and diarrhea. Due to the severe immune system suppression, multiple secondary infections develop, causing death within two to four weeks. Typical confirmation of the acute form of the disease is by necropsy, because it progresses too quickly for the normal signs such as feather loss and beak deformity to appear.

The chronic form occurs if the bird's immune system manages to mount a reaction to the virus and any secondary infections. The characteristic feather symptoms need time to develop, as they only appear during the first moult after infection. In those species having powder down, signs may be visible immediately, as powder down feathers are continually replenished.

Derzsy's disease is caused by a virus from the Parvoviridae family. It affects geese and Muscovy ducks.

The virus is shed in the faeces and thus transmission is horizontal, via the direct faecal-oral route and also indirectly via fomites. Vertical transmission is also possible.

Clinical disease only occurs in young geese and ducks between birth and 4–5 weeks of age.

Psittacine beak and feather disease (PBFD) is a viral disease affecting all Old World and New World parrots. The causative virus–beak and feather disease virus (BFDV)—belongs to the taxonomic genus Circovirus, family Circoviridae. It attacks the feather follicles and the beak and claw matrices of the bird, causing progressive feather, claw and beak malformation and necrosis. In later stages of the disease, feather shaft constriction occurs, hampering development until eventually all feather growth stops. It occurs in an acutely fatal form and a chronic form.

Cracking and peeling of the outer layers of the claws and beak make tissues vulnerable to . Because the virus also affects the thymus and Bursa of Fabricius, slowing lymphocyte production, immunosuppression occurs and the bird becomes more vulnerable to secondary infections. Beak fractures and necrosis of the hard palate can prevent the bird from eating.

The following signs and symptoms refer to epidemic typhus as it is the most important of the typhus group of diseases.

Signs and symptoms begin with sudden onset of fever, and other flu-like symptoms about one to two weeks after being infected. Five to nine days after the symptoms have started, a rash typically begins on the trunk and spreads to the extremities. This rash eventually spreads over most of the body, sparing the face, palms, and soles. Signs of meningoencephalitis begin with the rash and continue into the second or third weeks. Other signs of meningoencephalitis include sensitivity to light (photophobia), altered mental status (delirium), or coma. Untreated cases are often fatal.

Haverhill fever (or epidemic arthritic erythema) is a form of "rat-bite fever" caused by the bacterium "Streptobacillus moniliformis", an organism common in rats and mice. Symptoms begin to appear two to ten days after a rat bite injury. The illness resembles a severe influenza, with a moderate fever (38-40 °C, or 101-104 °F), chills, joint pain, and a diffuse red rash, located mostly on the hands and feet. The causative organism can be isolated by blood culture, and penicillin is the most common treatment. Treatment is usually quite successful, although the body can clear the infection by itself in most cases. Complications are rare, but can include endocarditis and meningitis.

Despite its name, it can present without being bitten by a rat.

The disease was recognized from an outbreak which occurred in Haverhill, Massachusetts in January, 1926. The organism "S. moniliformis" was isolated from the patients. Epidemiology implicated infection via consumption of milk from one particular dairy.

Acute disease leads to death in most birds between the ages of 7–10 days. Clinical signs are quite limited in those cases. Older animals tend to show severe systemic and neurological signs and diarrhoea.

Adults do not show any clinical signs.

Viral isolation should be attempted for diagnosis, and immunofluorescence and electron microscopy can confirm the viral infection. Pathological changes may also help the diagnosis.