Post-weaning Multisystemic Wasting Syndrome

Other papers and Comments on PMWS

Other names	PMWS
Causal agent	At present unknown. The most likely suspect is a pig circovirus 'type II' which is antigenically distinct from the widely distributed normal non-pathogenic pig circovirus 'type I'. Circovirus II (PCV II) can be isolated on nearly every farm. Circovirus are small non-enveloped DNA virus containing a unique single-stranded circular genome. There appears to be three major forms of PCV II referred to as a,b, and c– the b form is more commonly isolated from cases of clincal PMWS, however, the evidence is still being investigated to demonstrate any pathogenic differences. All three types occur in Australia – where PMWS is not recognised as a herd problem. Viral dendogram Australia
Distribution	The problem is recognised worldwide.
Age group	Post weaning from 4 to 16 weeks of age (15 -50 kg). Males more susceptible
Clinical signs
	Note this affects pigs 1 to 2 weeks after weaning it is very different from the wasting/poor weaner who fails to eat or drink adequately after weaning. These weaners have started to grow and then collapse quickly. Extremely poor response to antibiotics.
	Many pigs present with a high fever (40-42C)
	Affected pigs are listless and seek a cool area of the pen - near drinkers or along an outside wall
	Pigs waste very rapidly and develop a hairy coat and runted appearance
	Some pigs also may develop a slight cough, difficulty breathing and a slight diarrhoea, but this could be associated with secondary infections
	The lymph nodes may be palpable as grossly enlarged
	Pigs may go pale and yellow
	Generally this affects some 25% of the pigs in the pen, the remaining pigs can look well and unaffected. Mortality rates can exceed 25%
	The disease takes about 3 weeks to go through a group of pigs
	Many pigs will die although it will take several weeks.
	Conjunctivitis may be seen
	There increasing reports of latter abortion - neonate myocarditis
	Swollen lymph nodes are seen in the inguinal region and can be visualised and palpated		The pigs are wasted. They are often smaller than their pen mates. Secondary infections are common such as Glassers.
Infectivity
	Unknown, but circovirus I is very contagious. Circovirus is shed via most routes. Clinical signs are exacerbated with secondary diseases in particular active Parvovirus in growing pigs.

Post-mortem Lesions
	Post mortems can grossly be very disappointing or only reveal secondary infections with Pasteurella, streptococci or Haemophilus parasuis. However more detailed will reveal the swollen lymph nodes cases which progress to lymph node necrosis and reduction. Specific histological changes are being recognised - syncitial formation (cells merging together) and cytoplasmic basophilic intracellular inclusions. Lesions may be seen in 4 day old piglet heart muscle. Macrophages ‘soak’ up Circovirus II without significant change in their function. Circovirus II particles are therefore found in all areas where macrophages are working. Histological examination
There may be very few post mortem signs. In the pig above presented with enlarged lymph nodes. The liver was also a tan orange colour which is quite often seen.		The swollen lymph nodes in the inguinal region.	H&E section of lymph node. At histology intracytoplasmic inclusion bodies are seen. There is also a proliferation of cells in the lymph nodes. PCV II in immunohistochemistry
Diagnosis
	Clinical picture. There is no diagnostic test for the live animal. Circovirus serology not useful as too common.
	Post-mortem picture with swollen lymph nodes
	The histological picture from submitted lymph nodes, including IHC. Note that macrophages may carry the virus in large numbers without causing any impact on the macrophage function.
	Ruling out other causes
Treatment – see separate paper
	The circovacines are proving to be extremely effective in controlling the clinical signs of PMWS and where possible should be urgently considered as part of the control programme. However, note that these vaccines are extremely new and the situation must be watched with extreme caution.
	This is still under development as the disease becomes better understood more specific protocols can be advised. The following is a general guide only.
	Serotherapy can be used to good effect, discuss with your veterinarian
	Mange farm using all-in/all-out protocols. Age segregation may help control.
	Provide pigs with a good environment to limit effects of secondary infections
	Separate weaners who show signs of the disease to reduce the level of the disease in the pen
	Have good gilt introduction protocols to ensure gilts are well acclimatised before entry into the main unit.
	Feed-back of on-site nursery faeces is essential. Consider the use of tonsilar scrapes.
	Minimise cross-fostering
Common differentials
	Any other cause of wasting in 15 to 60 kg pigs, Glassers, chronic pneumonia, Ileitis, internal abscessation. Lymphosarcoma tends to affect individual older animals. The mortality levels are very high in PMWS

Papers on PMWS
Treatment and control of PMWS – personal observations