Infectious Diseases of Swine

1. Chaudhari¹, Jai Bhagwan², Vikram Jakhar³

¹ Extension Specialist, Pashu Vigyan Kendra, Sirsa, ²Assitant Professor, Lala Lajpat Rai University of Veterinary and Animal Sciences, Hisar

³Assitant Professor, Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana

In India’s tribal-dominated areas, pig farming is particularly vital for rural subsistence and food security. Despite its significance, piggery growth is on the decline, and the development of various infectious diseases is one of the biggest obstacles preventing piggery expansion in the nation. India has approx 9 million pigs, with 45% of them living in the country’s northeastern (NE) states.  Various infectious illnesses that pose a threat to the pig population have an impact on the export of pigs and swine products. Pig infectious diseases are significant because they result in significant economic loss due to the high morbidity and death of the affected animals. There are many signs and symptoms of ill health in pigs, some of the signs are as follows:

• Loss of appetite
• Loss of condition, and rough hair coat
• Mild fever or high fever
• Isolation from herd
• Passes excessively hard or watery faeces (diarrhoea)
• Difficult and abnormal breathing
• coughing, nasal discharge or eye discharge

1. African swine fever (ASF): ASF is a highly contagious devastating disease of pigs and wild boars causing 100% mortality. The causative agent of African swine fever virus (ASFV) belongs to the genus Asfivirus, family Asfarviridae. OIE has listed ASF as a notifiable disease. As per OIE published report of ASF in India on May 21, 2020, wherein, a total of 3701 pigs died from 11 outbreaks (Morbidity – 38.45% and mortality – 33.89%) in Assam and Arunachal Pradesh states of India. ASF is non-zoonotic. Pig is the only species affected by this virus. Soft ticks (Ornithodoros genus) are shown to be reservoir and transmission vectors of ASFV. Transmission is very rapid and quickly engulfs the entire pig population. It is very difficult to differentiate classical swine fever from ASF since the clinical symptoms overlap.

Signs and Symptoms:

• High fever 40-42°C.
• Loss of appetite.

• Depression.
• Lethargic- sometimes refusal to stand or move.
• unsteady when standing up.
• Vomiting and/or diarrhoea with bloody discharge.
• White skinned pigs: extremities (nose, ears, tail and lower legs) become cyanotic (blue-purple colour).
• Discrete haemorrhages appear in the skin particularly on the ears and flanks.
• Group will huddle together and are usually shivering.
• Abnormal breathing.
• Heavy discharge from eyes and/or nose.
• Comatose state and death within a few days.
• Some pigs can show conjunctivitis with reddening of the conjunctival mucosa and ocular discharges.

Diagnosis: By clinical or post-mortem examination, it is difficult to distinguish between CSFV infection and ASFV infection. Therefore, it is crucial to exclusively diagnose ASFV infections in laboratories. The goal of laboratory diagnostic methods is to identify the agent or the immunological response to the agent. Blood, serum, and tissues (including spleen, lymph nodes, bone marrow, lung, tonsil, and kidney) must all be sent for laboratory diagnosis. The best way to transfer the samples to the lab is on ice.

Biosafety and biosecurity measures: Farm level biosafety must be practiced. People or workers handling diseased pigs should follow all biosafety procedures, including donning protective gear such aprons, glasses, gloves, and gumboots, and avoiding going near other sheds. Gumboots should be cleaned with 2% sodium hydroxide right away after usage, and there are many commercial disinfectants on the market. Biosecurity must be practiced in farm, village, and neighboring areas. ASFV has been contained via isolation, movement restrictions, and sanitation (cleaning and disinfection).

Treatment: There is no vaccine available commercially.

2. Greasy Pig Diseases: An Acute, exudative dermatitis with varying mortality and morbidity that affects pigs between the ages of a few days and roughly eight weeks. This is caused by the bacterium Staphylococcus hyicuswhich invades abraded skin causing infection. Toxins produced by the Staphylococcus are ingested by the body and harm the liver and kidneys. Exudative epidermitis, another name for the illness, refers to the fluid that leaks from inflamed skin. In the sucking piglet disease is usually confined to individual animals, but it can be a major problem in new gilt herds and weaned pigs.

Signs and Symptoms: These usually commence with small, dark, localised areas of infection around the face or on the legs, where the skin has been damaged. The skin along the flanks, the belly and between the legs changes to a brown colour gradually involving the whole of the body. The skin becomes wrinkled with flaking of large areas and it has a greasy feel. A more localised picture is seen if the sow has passed some immunity to the piglet, with small circumscribed lesions approximately 5-10 mm in diameter that do not spread.

Diagnosis: Few swine diseases resemble typical EE. Signs and lesions usually are adequate for diagnosis. This is based on the characteristic skin lesions. Confirmation can be made by isolation of S. hyicus or by histopathology. In an outbreak it is important to culture the organism and carry out an antibiotic sensitivity test. A moist wet area should be identified, the overlying scab removed and a swab rubbed well into the infected area. This should be returned to the laboratory in transport medium to arrive as soon as possible, certainly within 24 hours.

Control and prevention: Treatment hasn’t generally been extremely effective. Antimicrobial injectables might be useful in some cases. According to anecdotal reports, it has been suggested to repeatedly spray the pigs with solutions like 10% bleach, chlorhexidine or diluted mild iodine. A few crucial actions must be taken at the farm level:

• Examine the pigs to see where abrasions are taking place. For example, these may be arising from new concrete surfaces or rough metal floors.
• If concrete surfaces are poor, brush these over after cleaning with hydrated lime that contains a phenol disinfectant.

• Check the humidity of the weaning accommodation. High levels above 70 percent and high temperatures provide an ideal environment for the multiplication of the bacteria on the skin.
• Disinfect the floors .
• Make sure that sharp needles are used for iron injections and change these regularly between litters.
• Check the procedures for removing tails and teeth. Jagged edges of teeth can damage the gums leading to infection around the cheeks particularly when piglets fight for teat access and during mixing after weaning.
• The skin of the udder is one reservoir of infection. This should be sprayed daily three days before and after farrowing with a iodine based skin antiseptic (cow teat dip is ideal).
• If mange is present in the herd treat the sow prior to entering the farrowing house.
• Extremes of humidity and wet pens can encourage the multiplication of the bacteria.
• Metal floors and side panels, in particular woven metal flooring, can cause severe abrasions particularly around the feet and legs. In such cases the first signs of greasy pig will be in these areas. Damage to the face by metal feeding troughs can precipitate disease.
• Adopt an all-in all-out policy in the weaning accommodation. Have the pens bacteriologically checked after they have been washed out and disinfected.

3. Streptococcus suis infection: Streptococcosis is regarded as a leading infectious disease in the swine industry, that clinically features with meningitis, septicemia, or arthritis and annually results in significant economic loss worldwide. S. suis is also an emerging zoonotic pathogen that causes severe human infections clinically featuring with varied diseases/syndromes (such as meningitis, septicemia, and arthritis).  human health burden due to infections worldwide, especially in Southeast Asia. At least five large outbreaks have been documented after the largest outbreak in China in 2005, which was related to the consumption of raw pork or dishes containing pig’s blood. Most clinically healthy pigs are carriers of multiple serotypes of S suis, although a few are colonized by virulent strains. Piglets become colonized with S. suis from vaginal secretions during parturition and while nursing. Asymptomatic carriers serve as a source of infection for their pen mates after they are mixed and commingled in the nursery, when maternal antibodies are no longer present. Clinical infections are seen mainly in weaned pigs (2–5 weeks after weaning), rarely in suckling and growing pigs, and almost never in adult animals. Transmission between herds occurs by the movement and mixing of healthy carrier pigs. The introduction of a highly virulent strain into a naive herd may result in subsequent onset of disease in weaned pigs.  The predisposing factors are:

• overcrowding
• poor ventilation
• excessive temperature fluctuations
• mixing of pigs with an age spread of >2 weeks
• co-infections with other pathogens

Signs and Symptoms: The major clinical features are sepsis or meningitis, with hearing loss a major complication of  S.suis disease. The earliest sign is usually fever, which may occur initially without other obvious signs. It is accompanied by a pronounced septicemia that may persist for several days if untreated. During this period, there is usually a fluctuating fever and variable degrees of inappetence, depression, and shifting lameness. In peracute cases, pigs may be found dead with no premonitory signs. Meningitis is the most striking feature and the one on which a presumptive diagnosis is usually based. Pigs in the early stages of meningitis may hold their ears back and squint their eyes. Other early nervous signs include depression, incoordination, and adoption of unusual stances (eg, dog-sitting), which may progress to inability to stand, paddling, opisthotonos, convulsions, and nystagmus. Even when the carrier rate in pigs is near 100%, the incidence of the disease varies from period to period and is usually < 5%. However, in the absence of treatment, mortality rates can reach upto 20%.

Diagnosis:

• The presumptive diagnosis is based on the patient’s history, clinical symptoms, and obvious lesions.
• Bacterial culture is used for confirmation.

Prevention and Control: Prompt recognition of the early clinical signs of streptococcal meningitis, followed by immediate parenteral treatment of affected pigs with an appropriate antibiotic, is currently the best method to maximize survival. Streptococci are susceptible to the action of aldehyde, biguanide, hypochlorite, iodine, and quaternary ammonium disinfectants.

4. Salmonellosis in Pig

Salmonellosis is the disease caused by any of more than 2000 Salmonella serotypes. In swine, only a few serotypes can cause disease, usually manifested as septicemia and/or enterocolitis, sometimes by tissue localization of infection at various sites. Salmonella infections in asymptomatic swine may serve as a source of Salmonella infection to humans via contamination of pork products. Enteropathogenic salmonellae cause inflammation and necrosis of the small and large intestines, resulting in diarrhea. Infection with certain serotypes may be accompanied by generalized sepsis. Pigs of all ages are susceptible; however, intestinal salmonellosis is most common in weaned and growing-finishing pigs.

Signs and Symptoms: Intestinal salmonellosis is most often observed in pigs from weaning up to about 5 months old; however, it can occur at other ages also. Affected pigs are commonly febrile, with reduced feed intake, and have liquid yellow feces that may contain shreds of necrotic debris. Diarrhea in individual pigs usually lasts 3–7 days, and it may recur for multiple bouts. Few prominent signs are indicative of salmonellosis:

• High temperature.
• Depression.
• Loss of appetite
• Ears, nose and tail congestion (septicemia).
• Pneumonia.
• Coughing.
• Nervous signs (rare).
• Smelly diarrhea, which sometimes can have blood and mucus.
• Might die in the acute phase of the disease.

Control and Prevention:

• Improve hygiene by ensuring proper cleaning and disinfection.

• All-in-all-out pig flow.
• Purchase animals (including breeding stock replacements) from known negative sources.
• Vaccines can be very effective (do have some cross protection between S. Choleraesuis and Typhimurium).
• Antibiotics can control disease but will not eliminate the pathogen.
• Do not use animal fat in diets.
• Control rodents.

African Swine Fever: An Emerging Threat to Piggery Industry in India  

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