farm animal cannibalism strikes again

Farm animal cannibalism strikes again?

Cannibalism is one of those practices that, at least as far as humans

go isn't very high on the list of things that are socially acceptable.

One of the numerous problems with cannibalistic practices is the

transmission of diseases, after all what infects dinner is just as

easily going to infect the cannibal. It should be reasonable common

sense as a result not to feed a farmed animal the remains of their

fellow animals. This would greatly aid the spread of an infectious

microorganism through a herd and possibly even rapidly increase

virulence (which is often directly correlated to the ease of

transmission).

The case example of why this practice shouldn't be performed, with any

(BSE) in Britain. BSE was found to be spread by an infectious protein

called a prion, which is predominantly found in the brain and spinal

matter of the remains of cattle. Worse, these parts were frequently

fed back to other cattle as a supplement to their feed, providing an

easy method of transmission for the infectious prions. The worst part

of the entire discovery was not just that other cattle could be

infected in this manner, but the potential spread of the disease

between beef from infected cattle and humans. This led to the culling

and suffering of a large number of animals and an overall ban on

British beef that lasted a considerable time.

The entire result was a heavy economic and consumer confidence toll on

British farmers and on the entire beef industry that cost millions

(billions?) of pounds. Predictably, the practice of feeding dead

cattle back to other cattle was immediately halted. With such a

brilliant example of why allowing cannibalism with farm animals is a

silly, you would probably imagine that most places would ban the

practice regardless of species. Unfortunately, an outbreak of a

disease among pigs on South Island farms recently in New Zealand, may

be linked to feeding pigs the remains of other pigs imported from

overseas (emphasis in the quote below is mine and I shortened the

length, indicated by the ....)

An animal health expert says a pig disease that has struck the

heart of New Zealand's pork industry is almost certainly

Post-weaning Multi-systemic Wasting Syndrome (PMWS).

PMWS is a highly contagious viral disease that kills young pigs up

to 12 weeks old. It has forced the closure of about six pig farms

in the North Island.

Vets have been investigating a disease outbreak that has so far

killed about 1,000 piglets on eight to 10 farms near Christchurch

in Canterbury.

...............

He says it is possible that the Canterbury PMWS outbreak has been

caused by infected imported pig meat being fed to pigs in foods

scraps.

Feeding waste material to pigs has recently been banned again.

Obviously this is a severe disease and has resulted in a heavy

economic loss for several farmers. The disappointing part is that

lessons of the past from the emergence of BSE clearly weren't heeded,

especially if the outbreak is conclusively found to be linked to

cannibalistic practices. Although the disease, called Post-weaning

Multi-systemic Wasting Syndrome or PMWS is not suspected to be

dangerous to humans, the outbreak still demonstrates important

principals about how diseases may result from farming practices.

PMWS is caused by a virus called porcine circovirus 2 (PCV2), which

was first identified in 1997 and is probably one of the most puzzling

diseases around. PMWS is diagnosed not by using molecular techniques

such as antibodies, but instead through the manifestation of certain

symptoms that occur over the course of an infection. This is because

antibodies to PCV2 can be detected amongst herds that do not show any

overt signs of disease, indicating the organism is present but

inexplicably not causing an infection. As a result, the following

clinical symptoms are used to describe the disease: wasting (rapid

loss of body weight), dyspnea, enlarged lymph nodes, diarrhea, pallor

(loss of skin colour) and jaundice. Additionally, in some cases

animals may exhibit coughing, pyrexia (a fancy term for fever),

gastric ulceration (often leading to anemia), meningitis (an infection

of the meninges surrounding the brain) and dropping dead (which is

terminal).

How PCV2 causes such a wide array of symptoms and even how it

initiates disease is the puzzling aspect about it. Experimental animal

models have largely failed to reproduce the disease by using PCV2 by

itself except in certain cases. Interestingly, more success has been

attained when PCV2 was injected with other viruses, such as Porcine

parvovirus. Regardless of the mechanisms that determine if the virus

becomes infectious, when PCV2 does it targets some of the most

vulnerable members of the herd, namely piglets aged between 7-15 weeks

old. Possibly the most striking characteristic of PMWS is the overall

mortality rates in infected animals, potentially getting as high as

40% and can even induce pregnant sows to abort their fetuses.

Dealing with the virus is equally difficult, because it tends to be

widespread throughout the herd and circoviruses are notoriously

difficult to kill with antiseptics and detergents. Containment and

control requires more practical, such as reducing herd sizes, keeping

animals separated by age and reducing animal density. As can be seen,

the biology PVC2 and the linking of the outbreak to imported pig meat

being used on the farms, raises an intriguing hypothesis as to the

potential aetiology of the disease. Let us imagine a potential

scenario from a land far, far away....

On a farm in an unknown land, a sick piggie called Mr. Pork wakes

up to a pretty bad headache among other things...

Mr. Pork: Owww my head, I feel under the weather here. I know, I'll

go to farmer Brown for help! He'll know what to do!

Farmer Brown: Why hi there porkie, how's your day going?

Mr. Pork: I'm feeling a bit under the weather here and I may be

getting ill!

Farmer Brown thinks to himself: I'd better do something about this

before it spreads!

Farmer Brown: Well I have just the solution there Mr. Pork, we

should go and visit Dr. Mallet. He'll fix you all up!

Mr. Pork: Oh that sounds great, let's go and -

Image hosting by Photobucket. Image originally from an article

written by the onion www.theonion.com *CLUNK*

Farmer Brown: Off to the sausage factory for you!

Later at the pork to sausage factory....

Worker 1: What are we going to do with all the left-over pig bits?

Worker 2: Let's package them up as supplemental feed and send them

to New Zealand.

Worker 3: Genius!

Anyway, returning from the realm of imagination, there may be solid

indications that this is a possible origin of the PMWS outbreak in New

Zealand. The suspected causative agent PCV2 has already been widely

identified in New Zealand pig herds, and has caused outbreaks in the

North Island previously. It is theoretically possible that a disease

transmitted from infected pigs overseas, such as a different serotype

of Porcine parvovirus that is not immunologically present here in New

Zealand was in the imported meat. Once fed to the pigs on the farms in

question, it encountered the `native' PCV2 and potentially triggered

the silently waiting virus to a full blown infectious disease.

Of course, this is not the only explanation but given the biology of

the disease it's a fairly compelling place to at least make a start.

This is of course where one would expect the government to step, but

unfortunately, it doesn't actually appear such assistance is going to

be quite what some farmers may expect:

Canterbury pig farmers at the centre of a disease alert have been

given a clear message from the government that it will not step in

with an eradication plan.

The Ministry of Agriculture and Forestry's Biosecurity Authority

has advised the government that eradication of the suspected

disease, PMWS or Post-weaning Multi-systemic Wasting Syndrome, is

not viable.

Well, that almost sounds to me as if they are throwing in the towel

before they even try to do anything. At the very least, by identifying

why the outbreak occurred and potentially trying to contain or

eliminate the cause authorities could do a fair amount of good. While

I do suspect that elimination of PVC2 may be unfeasible although

containment and other measures should at least be attempted. If there

is a positive to be taken from the recent outbreaks, it's that feeding

pig remains back to other pigs has been re-banned. I guess you take

your victories where you can get them.

References

Chae C. (2005). A review of porcine circovirus 2-associated syndromes

and diseases. The Veterinary Journal, 169:326-336.

Darwich L., J. Segal and E. Mateu (2004). Pathogenesis of postweaning

multisystemic wasting syndrome caused by Porcine circovirus 2: an

immune riddle. Archives of Virology, 149:857-874.