Disease scares from our live-stock and food animals

Hi,

Today I will write about the Ebola scare in pork from the Philippines.

Bird flu from China, Sars from Hong Kong, Measles, Cow pox, Mad Cow disease, small pox, Hepatitis, Rabies, AIDS, foot and mouth disease...What do they all have in common?

Answer: They are all diseases that spread from a host animal to man. In the host animal, these diseases are usually not deadly (benign) and they might cause discomfort but not necessarily death.

Some of these disease have been around longer than others. The newer ones are HIV (reported first in 1981 but thought to have originated in non-human primates in sub-Saharan Africa and transferred to humans early in the 20th century.), Ebola in Africa (reported in 1976), Ebola in Philippines (reported in 2008), SARS in China (reported in November, 2002) and Mad Cow Disease (first described in 1921 as Creutzfeldt-Jakob disease with a new variation from eating infected cows emerging in Britain in the mid-1980s).

• Bird flu was first documented as a pandemic in 1918-19; measles was first documented by the Persian physician, Muhammad ibn Zakariya ar-Razi (860-932) and the virus was isolated in 1954.
• Small pox has infected humans for 12,000 years; inoculation of material from smallpox blisters to induce a mild infection was possibly practised in India 3,000 years ago but is documented in China from the 10th Century. This was effective at giving immunity but risky. Edward Jenner in England documented the benign disease, cowpox, as a safe immunisation method in 1796 and thus created the first vaccine.
• Cholera first caused a pandemic in 1816 in Bengal, India. It has no particular animal host but survives in aquatic environments between outbreaks.
• Rabies is a disease of mammals; the name 'rabies' originated at least 5,000 years and was first written about around 1930 BC.

I will write about these in other posts.

What do all these diseases have in common?
The pathogens or causative agents all originated in animals that man handles either as food, as draught or transport animal, or came into contact accidentally.


Ebola in pigs in the Philippines
This is the latest scare, reported on 10th Dec 2008. Pork from 4 piggeries in northern Philippines showed the presence of Ebola-Reston virus.

It was first reported in crab-eating macaque (monkeys) in 1989. Two more outbreaks occurred in 1992 and 1996 in Southern Philippines and it was always confined to the monkey population and people in direct contact with the infected monkeys. It produced flu-like symptoms. The Philippine strain is a non-fatal.

What is so scary about this Ebola if it is never fatal in monkeys?
Ebola-Reston is a monkey virus that produced flu-like symptoms in monkeys and man. When it jumped species, as it did in Dec 2008, and started infecting pigs, then there is a chance that a mutation has occurred and the virus is now a virulent and fatal strain. If the changes that it has inherited makes it possible to jump species to man and people who handle the pigs in piggeries, then it can spread into the general population, i.e. people who do not go near a live pig but only eat pork and live in a neighbourhood where piggery workers live.

Why does the word Ebola evoke such fear in scientists?

SIDE NOTE: Diseases that originated in or are harboured by other animals are called 'zoonoses', or zoonotic diseases. Generally, humans get infected by accident and it is a dead end for the organism, even when they cause major pandemics like bubonic plague. Eventually, humans become too few in numbers where the outbreak occurs, either through death or by gaining immunity and the bug goes back to their natural host. By this definition, malaria is not a zoonosis — the disease needs to pass through both humans and mosquitoes to survive. Sometimes a mutation occurs and a new disease arises that depends solely on humans, like measles, which could have come from cattle or dogs. In other words, the disease can now spread from person to person with the need of any animal host

There are 3 other types of Ebola in Africa which cause fatal haemorrhagic fever and have killed hundreds. That it has not killed mny more is partly due to the extreme fear it induces in people, who flee the towns and villages where it breaks out. If the new strain of virus in pigs is virulent like the ones in Africa, its impact on humans is unimaginably unknown.
Three global watchdogs, the World Health Organisation, the United Nations' Food and Agriculture Organisation, and the World Organisation for Animal Health are testing these farm and the slaughterhouse workers for the virus. Pork from these farms are tested and people in the Philippines are asked to eat only well cooked pork. Pigs from the 4 affected farms are quarantined and transport of pigs from these farms is not allowed.

Why are so many of these new disease deadly? Why are we not afraid of the good old common cold?
These are new diseases to man. The human body has evolved its own immune system over millions of years to protect the body against human diseases. The body's white blood cells "recognise" the old germs (pathogens) and have the correct ammunition to kill them and protect the human body from the invaders. However, when pathogens from other animals get into our body, our body do not even recognise them as pathogens, and leave them alone to ravage the human body. An analogy would be, if the enemy only wears red for many generations, and an enemy that wears green comes along, our armies do not even know that they are enemies and turn a blind eye towards them. The enemy will have a free hand to pillage and plunder your country (=your body). As scientists say, we are "naïve" to the pathogen.

A child with smallpox. Fortunately, smallpox is now extinct — the first disease in history to be eliminated forever.

Hellish Ebola in Africa, for man and gorilla

Ebola haemorrhagic fever was first documented in 1976 in Zaire and Sudan in Africa. It spread rapidly from human to human through to contact with body fluids and blood. It is also spreading fast within the Lowland Gorilla population too, and caused tens of thousands of deaths in the past decade.

A biosuited scientist (top) and a dead gorilla. Click the gorilla image to find out why Ebola is such a serious problem for gorillas and how they can be helped

The host species for the virus is a fruit bat. (The bat does not get sick and is a natural reservoir of the virus.) When the virus jumped species from bat into man or gorilla, it caused internal(haemorrhagic) and external bleeding, fever and diarrhoea and eventually 50% to 90% of the infected died painful and rapid deaths. The disease is not treatable as no vaccines exists for it.

Protozoa, bacteria, viruses and prions (non-living protein disease-causing agents) reproduce much faster than we do. So they can evolve new ways to breach our defences faster than we can acquire natural immunity (which can be gained only at a cost of death and illness). They also thrive in conditions of high population densities and poverty that exist in much of the world. We rely on human ingenuity to devise treatments like new drugs, and preventives like hygiene and vaccines to overcome these shortcomings.

Cheers