Animal flu, also known as animal influenza, is a disease caused by animal influenza viruses. Influenza is a respiratory illness common among humans and a handful of some animal species, some domestic and wild birds, chickens, ducks, pigs, horses, including some aquatic animals like whale and farm carnivores.
However, animal flu can cross the specie line and infect humans. Occasionally, humans can be infected usually through direct contact with an infected animal or contaminated environment.
These infections, in rare cases, transmit between humans. Animal flu can cause diseases in humans ranging from mild flu to severe pneumonia and death.
There are subtypes of the animal flu such as Influenza A, B, C and D virus. The Influenza A virus is divided into subtypes. This is based on the proteins on the surface of the virus: the Hemagglutinin (H) and the Neuraminidase.
Under the Hemagglutinin, there are 18 different subtypes, and under the Neuraminidase, there are 11 different subtypes.
There are others like the avian influenza virus subtypes A(H5N1) and A(H9N2) and swine influenza virus subtypes A(H1N1) and (H3N2). Other animals like horses and dogs also have their assortment of influenza viruses.
If such a virus acquired the capacity to spread sustainably from one person to another, it could start a pandemic because it would be so new that humans would have little immunity to it.
Over the past decades, there have been multiple instances of sporadic transmission of influenza viruses between animals and humans.
When animal influenza viruses infect their natural animal host, they are named for that host, as in avian influenza viruses, swine influenza viruses, equine influenza viruses, and many more.
As such, the term “swine flu” refers to swine influenza viruses infecting swine.
Table of Contents
There are four types of influenza viruses: types A, B, C and D:
- Influenza A viruses infect humans and animals as well. This makes it a matter of concern because the emergence of new and different influenza A virus, it has the ability to infect people and has sustained human to human transmission that can cause an epidemic or worse, a pandemic.
- Influenza B viruses are transmitted among humans. Recent research shows seals also can be infected.
- Influenza C viruses can infect both humans and pigs, but infections are generally mild and are rarely reported.
- Influenza D viruses primarily affect cattle and are not known to infect humans.
Signs and symptoms of animal flu in humans
Animal flu infections in human can cause diseases from mild respiratory infections like fever and cough to severe symptoms like pneumonia, acute respiratory distress syndrome, shock, and in some cases, death.
Disease features such as the incubation period, severity of symptoms and clinical outcome varies by the virus causing the infection but mainly manifests with respiratory symptoms.
In patients infected by A(H5) or A(H7N9) avian influenza viruses, the disease has an aggressive clinical course. Common initial symptoms are high fever (greater than or equal to 38°C) and cough followed by symptoms of lower respiratory tract involvement, including dyspnoea or difficulty breathing. Upper respiratory tract symptoms such as sore throat or coryza are less common.
Other symptoms such as diarrhoea, vomiting, abdominal pain, bleeding from the nose or gums, encephalitis, and chest pain have also been reported in the clinical course of some patients.
Complications of infection include severe pneumonia, hypoxemic respiratory failure, multi-organ dysfunction, septic shock, and secondary bacterial and fungal infections. The fatality rate for A(H5) and A(H7N9) subtype virus infections among humans are much higher than that of seasonal influenza infections.
For human infected with avian influenza A(H7N7) and A(H9N2) viruses, the disease is typically mild or subclinical. Only one fatal A(H7N7) human infection has been reported in the Netherlands so far.
Humans infected with swine influenza viruses have exhibited mild symptoms with few hospitalized. There have also been few reports of deaths resulting from infection.
For a correct diagnosis, laboratory tests are required. WHO, through Global Influenza Surveillance and Response System (GISRS), regularly update protocols of technical guidance to detect animal flu in humans.
The methods used in diagnosing animal flu include molecular like RT-PCR.
There are Rapid influenza diagnostic tests (RIDTs) which have lower sensitivity compared to PCR, and the accuracy and reliability of the results depend mainly on the conditions which they are used. Commercially available RIDTs, in general, cannot provide subtype information. Their use in detection of the animal flu is limited.
Evidence proposes that antiviral drugs like neuraminidase inhibitor (oseltamivir, zanamivir) can reduce the duration of viral reproduction and improve the chances of survival. However, clinical research is still needed.
The emergence of oseltamivir resistance has been reported. In confirmed cases, neuraminidase inhibitors are prescribed, optimally, within 48 hours following the onset of the symptoms.
This is to utilize therapeutic benefits effectively. Usually, treatment is recommended for a minimum of 5 days until there is a satisfactory clinical recovery.
Prevention, they say, is better than cure. Apart from antiviral treatment, some personal protective measures proposed by public health management include:
- Regular washing of hand or using an alcohol-based hand sanitizer
- Practising good respiratory hygiene like covering one’s mouth and nose when coughing or sneezing, using tissues and disposing of them properly in a waste bin
- Isolation of those with flu symptoms like coughing, sneezing and fever
- Avoiding close contact with people exhibiting flu symptoms
- Avoid touching one’s eyes, nose or mouth as these are pathways the flu virus can enter the body
- People travelling to countries with known outbreaks of animal flu should avoid poultry farms, contacts with animals in poultry markets and areas where poultry may be slaughtered
- Avoid contact with hard surfaces that may or may not appear contaminated from poultry or other animals
- Travelers returning from affected regions should report to health services if they have any respiratory symptoms or fever
- Influenza (Avian and other zoonotic) – WHO