Swine Influenza

Other names	Swine Flu, Flu, Influenza
Causal Agent	Swine Influenza Virus. This belongs to the Influenza type A virus group. In the USA H1N1, H3N2 and reassortant H1N2 are problematic. The US has also developed a novel H1N1 with avian internal genes. Currently common varieties within the UK are H1N1, H1N1 (195852), H3N2 and H1N2. There are 16 H and 9 N types providing a lot of potential. There are at least 7 different pig adapted influenza viruses. The genome is divided into 8 segments.
Age group	All ages can be affected
Clinical signs
	Naive herds Explosive outbreaks with all or many animals becoming ill at the same time.
	Disease much more common in the Spring and Autumn
	Animals present with inactivity, depression, huddling/pilling. They are anorexic. The animals often are mouth breathing and breathing is laboured. When the animals are moved many cough, some uncontrollably (paroxysm coughing). They often have a nasal discharge and the eyes are puffy. Their rectal temperature increases to 40.5-41.5•C. As the disease progresses loss of weight may be seen. Mortality is generally low. The high rectal temperature in breeding stock can result in abortions, infertility (a boar can become sub-fertile for 6 weeks), production of small weak litters and increased stillbirths. Recovery generally starts 5 to 7 days after the first clinical signs
	Established Herds Annual re-infection appears, possibly from carrier pigs or the natural spread to younger naive pigs who present few signs in the summer months.
Infectivity
	The disease is much more predominant in the spring and autumn months, however antibody investigations reveal little seasonal trend implying pigs get sick during the summer months without presenting with many signs
	Spread is mainly from pig to pig via the movement of animals, introduction of breeding stock
	Cross-Infectivity between human, pig, duck and turkey strains can occur
	Humans can transmit the disease to pigs and vice versa
	Virus can survive in the environment for a very short period of time.
Stress factors
	Moving pigs
	Mixing pigs
	Poor isolation facilities
	Marked diurnal (day and night) temperature fluctuations
	Overstocking
Incubation period
	1 to 3 days. Can be as short as 4 hours

Post-mortem Lesions
		There may be few lesions seen in uncomplicated cases. There may be firm lobular lesions with interlobular oedema. Associated lymph nodes may be enlarged. The trachea can be filled with froth. The Swine Influenza causes problems because it damages the lining of the trachea destroying the mucociliary escalator. In combination with pasteurella the gross appearance of the lung is extremely similar to Mycoplasma hyopneumoniae infections.
Diagnosis
	Clinical signs
	Use of histology from fresh lungs and stained with antibody stains For example, the picture shows the microscope view, the brown areas represent swine influenza
	Paired blood samples checked for antibody concentrations (21 days apart), note maternal antibodies may persist for 2-4 months
Treatment
During outbreak	Cover all services with AI from a third party source
	No specific treatments available, all treatment regimes supportive
	Careful nursing in the farrowing house essential. Must ensure the farrowing house is draught free.
	All-in/All-out will limit the spread of the disease
	Provide fresh clean drinking water
Control	Avoid ducks and turkey contamination's contact including staff
	Use disinfectants when cleaning buildings
	Vaccines. Note vaccines do not provide lifelong immunity – 6 to 9 months Do not allow clinically affected people to work with pigs or on AI stations
Elimination	Elimination is worth while on breeding stock farms or in previously negative regions.
Common differentials
	Enzootic pneumonia. Other causes of reproductive problems. PRRSv
Zoonotic implications
	Swine Influenza may rarely affect human beings – Influenza A (H1N1)2009 for example. There is no risk to eating or handling pork or pork products

Treatment advice for pigs with Swine Influenza

Further detail of the Influenza A (H1N1) virus – virus evolution tree and discussion

Elimination strategies for swine influenza

Swine Influenza – A moving genetic target

Basic make up of the Influenza Virus
Swine influenza belong to the family – Orthomyxoviridae group A. The geneome is segmented into 8 negatively sensed RNA pieces. The virus is enveloped. The picture shows an electronmicroscope picture of an influenza virus and a pig with swine influenza
There are two major surface antigens – H – There are 16 possibilities N - There are 9 possibilities Major species with influenza viruses: Bird (most species) Mammals – Man, Horse, Pig.
Swine Influenza can change by two major methods:
Genetic Drift
Here parts of the genetic code changes with replication errors. This is typical of an RNA virus
Genetic Shift
Here recombination of different viruses occupying the same cell at the same time – make a new type of virus.
Examples:
Current Swine Influenza viruses of importance are H1N1, H3N2, H1N2 . There are some 7 different major types of Swine Influenza virus recognised. Note that there are differences between European and American strains, even with the same type of H or N they may originate from difference species ie avian or mammal.

Further detail of the Influenza A (H1N1) virus – virus evolution tree and discussion