Swine flu; a zoonotic disease

The spread of swine influenza in the United States created a worldwide scare recently. Transmitted by airborne droplets from an infected person’s sneeze or cough, or from germs on hands, or germ-laden surfaces, the swine flu virus mutates so that it can infect humans and be spread by humans. Swine flu is a type an influenza virus that causes respiratory illness in pigs. People do not normally get swine flu, but human infection can and do happen. What is particularly worrying about the current swine flu infecting pigs and human is that the H1N1 virus is a genetic mix of swine, human and avian flu strains, a dangerous combination that could elude traditional drug treatments.
The threat of zoonosis, where a disease jumps from animal to human like HIV, Anthrax, Bird flu, and in the most recent instance, Swain flu, is growing rapidly. Zoonosis is a category of infectious diseases where the pathogen is able to cross the species barrier from wild or domestic animals to humans. A major factor contributing to the appearance of new zoonotic pathogens in human populations is increased contact between humans and wildlife. This can be caused either by human encroachment in wild areas or by movement of wild animals into areas of human habitations caused due to environmental disturbance.

Microorganism-host relationship;

In, nature, microorganisms exist in harmony with their hosts co-evolve, the hosts progressively become resistant to the microorganisms. When a microbe jumps from a long-standing animal host to human beings, it may cease to be a harmless parasite and become pathogenic. To survive, a pathogen has to be a chronic infection, stay alive in the host for a long time or have a non-human reservoir in which to live while waiting for new hosts to pass by. In fact, the human is actually an accidental victim and a deal-end host for many human diseases like rabies, anthrax, tularemia, West Nile virus and many others.
Most of the modern infectious diseases emerged as zoonotic infections. It is difficult to determine which diseases jumped from animal to humans, but there is good evidence that measles, smallpox, influenza, HIV and diphtheria came to humans by microbes jumping from one species to the other. H5N1 is a strain of avian influenza / bird flu but there is evidence of its attack on jumped from civet of humans probably because of inadequate cooking of civet meat for human consumption. Similarly, West Nile virus has spilled over into human populations probably due to interactions between the carrier host and domestic animals. This virus is part of the Japanese encephalitis antigenic complex of viruses. It mainly infects birds. However, cases of infection by this virus have also been reported in humans and domestic animals. The main route of human infection is through the bite of an infected mosquito.

Preventing zoonotic diseases:

-Strictly avoid undercooked/ raw meat, unpasteurized dairy products and unwashed vegetables.
- Limit travel to areas where a new pathogen has been found.
- Increase farm hygiene.
- Clean and disinfect transport cages, feed trays and any equipment after each use.
- Observe domestic animals daily for clinical signs of diseases and report abnormalities to help in early veterinary investigation.
- Immediately move highly endangered or susceptible species to the most secure facilities available within the zoo and keep in isolation.
- Dispose carcasses to minimize transmission of pathogens to human or other animals within the vicinity.
- Decontaminate/ disinfect highly susceptible areas.
- vaccinate poultry and domestic livestock.
- Vaccinate poultry and farm workers compulsorily.
- Reduce contact between livestock and wild birds.
- Make available veterinary vaccines.
- Ban bush meat and exotic pet trade.
- Conduct public awareness programmes.

Classification of influenza:

Of the three genera of influenza viruses that cause human flu, two also cause influenza in pigs, with in influenzaA being common in pigs and influenzaC being rare. InfluenzaB has not been reported in pigs.
InfluenzaC:
InfluenzaC viruses infect both human and pigs, but do not infect birds. Transmissions between pigs and humans have occurred in the past. For example, influenzaC caused small outbreaks of a mild from of influenza amongst children in Japan and California. Because of its limited host range and lack of genetic diversity in influenzaC, this form of influenza does not cause pandemics in humans.
InfluenzaA:
Swine influenza is known to be caused by influenzaA subtypes H1N1, H2N3, H3N1 and H3N2. In pigs, three influenza a virus subtype (H1N1, H2N2 and H3N2) are the most common strains worldwide. In the United States, the H1N1 subtype was exclusively prevalent among swine populations before 1998; however, since late August 1998, H3N2 subtypes have been isolated from pigs. As of 2004, H3N2 virus isolates in US swine and Turkey stocks were triple reassortants, containing genes from human (HA, NA and PB1), swine (NS, NP and M), and avian (PB2 and PA).

EMERGIMG DISEASE

It was in April 2009 that swine flu first raised its ugly head in the developed countries where timely and efficient medical care facilities helped to control the diseases. As the developing world, with limited resource and poor health condition, came under the grip of H1N1influenza virus, alarm bells began to ring. In no time, the disease assumed pandemic proportions as it rapidly spread to all parts of the world, killing more than 4000 people worldwide in a span of just six month.
The reasons for the emergence of new infectious disease is not far to seek. Habitat destruction is one. It includes conversion of forest land to agriculture, urban sprawl, infrastructure development and other changes to the characteristics of the ecosystem, construction of houses in rural areas forces animals to live in crowed population, giving opportunities to microbe to mutate and emerge as new pathogens.
Population increase will be most dramatic in the poorest and least urbanized continents, Asia and Africa. Surveys indicate that all urban growth over the next 25 years will be in developing countries. One billion people, one- sixth of the worlds population, or one third of urban population, now live in slums, which are seen as breeding grounds for problems such as malnutrition, non-availability of portable water , pollution and poor sanitation-all of which contribute to high incidence and play crucial role in their spread.
Another important but neglected reason, as far as zoonosis concerned, is global warming. Climate warming allows microorganisms to move into new areas where they may harm diverse species. Pathogens that have been restricted by seasonal temperatures can invade new areas and find new victims as the climate warms and winter grow milder. Even one to two degree change in temperature can lead to disease outbreaks. Warming temperature allows insects and microbes to invade areas where they once were barred by severe seasonal chills. Many pathogens multiply more often in warmer temperatures.

POTENTIAL GEOGRAPHICAL LOCATIONS

About 40% of the world’s population lives in the tropical zone. The tropical climate is warm to hot and moist year around. As a result, exotic disease is mostly reported in tropical areas. In addition, large volumes of rains favor the formation of breeding grounds and high number and variety of natural reservoirs and presence of insect vectors of diseases. Higher temperatures may favor the replication of pathogenic agents both inside and outside the body of organisms. In comparison, in the temperate zone \,disease are less prevalent because of cold season; insects go in hibernation during the cold season and thus their population growth is arrested to some extent.
Increase in global temperature is causing tropical disease and vectors to spread to higher altitudes in mountainous region and to higher latitudes that were previously spread. Thus, the tropics with their biodiversity and favorable climate for microbial growth and the evolution are the potential place for the emergence of new disease. So, it can be safely concluded that future hot spots for occurrence of new disease are more likely to be found in the wildlife rich and the population dense tropics, especially in the highly populated cities.
Countries of southern Asia and Southeast Asia are tropical countries rich in biodiversity overpopulated. Hence, these countries too are at risk for emergence of new disease. India too cannot escape the specter of the appearance of new bugs. And hence Nepal is also at risk because of the open border with India.

Signs and symptoms

In animals like pigs:
-Fever
-Lethargy
-Sneezing
-Coughing
-Difficulty breathing
-Decreased appetite
-Abortion (in some cases)
-Mortality (around 1-4%)
-weight loss
-Poor growth
Infected pigs can lose up to 12 pounds of body weight over a 3 to 4 week period.
In humans:
-Fever
-Cough
-Sore throat
-Body ache
-Headache
-Chills
-Fatigue
-Diarrhea and vomiting (in some case).
-Respiratory illness.
Signs of death:
-Respiratory failure.
-Pneumonia (leading to sepsis).
-High fever (leading to neurological problems).
-Dehydration (from excessive vomiting and diarrhea).
-Electrolyte imbalance.
-Kidney failure.