Martin Henry: New diseases, old battles
On World Mosquito Day (August 20), the KSAC and the South East Regional Health Authority teamed up for a town square meeting in Mandela Park on chik-V and ZIKV, two new mosquito-borne diseases. A much less exciting affair than the gatherings in the same space to watch and celebrate the performance of our athletes at the World Championships. But far more important.
A frightening flow of new diseases is heading our way, along with the rest of humanity, diseases like chik-V, which has already ravaged Jamaica, and ZIKV, which is out there somewhere and coming. And these are not the worse. While they will make us sick, the kill rate of these diseases is quite low. Ebola, another new disease that has recently ravaged three West African countries and scared the whole world, with cases imported into Europe and North America, has had an average mortality rate of around 50 per cent, but mortality has been as high as 90 per cent in previous outbreaks.
The Mosquito Day meeting in the park was held to outline Jamaica's Preparedness and Response Plan for ZIKV. The Zika virus is carried by the Aedes aegypti mosquito, like chik-V and dengue. Aedes is one of the top three varieties, out of some 3,000 species of mosquitoes which are responsible for transmitting dangerous diseases to more than 700 million people mostly in the tropical developing world, with at least two million people dying each year from these mosquito-borne diseases. The other members of the Big Three are the Anopheles group for malaria, etc, and the Culex group carrying, among other things, the West Nile virus, which is a relatively new disease.
There are basically three approaches to controlling infectious diseases: Vaccines that prevent the disease and which have worked marvellously well against old worldwide disease scourges like polio and smallpox; antibiotics that inhibit or kill the microorganism causing a disease and which brought diseases like tuberculosis (TB) under control; and control of transmission by a variety of means, depending on how the disease is spread from person to person. Means like clean water, clean food, clean hands, and the reduction of vector populations.
Clean water brought typhoid under control. And mosquito control brought malaria under control in many countries. Jamaica was declared malaria-free in 1963, lots of thanks to the insecticide, DDT, which has since been banned across the world as too environmentally dangerous to other things beside the target mosquitoes.
RESURGENCE OF INFECTIOUS DISEASES
The problem with these massive successes is that these very successes are now helping to drive a resurgence of infectious diseases. Antibiotics have pushed the emergence of resistant strains of old diseases like TB. Insecticides used against vectors have helped to generate more resistant strains. The US Centres for Disease Control and Prevention (CDC) tells us that "each year in the United States, at least two million people become infected with bacteria that are resistant to antibiotics and at least 23,000 people die each year as a direct result of these infections".
In one of its annual reports a few years ago, the World Health Organization (WHO) warned that "new diseases are emerging at an unprecedented rate, of one a year, and are becoming more difficult to treat", with science struggling to keep up as diseases increasingly become drug resistant.
The world, the WHO predicted, will face some new deadly threat on the scale of AIDS, SARS and Ebola within a decade, as it warned that diseases were spreading more quickly than at any time in history.
That report identified 40 diseases unknown a generation ago, and indicated that over the five years before the report, the WHO had verified more than 1,100 epidemic events around the world, some of these involving new diseases.
The WHO says, "Gains in many areas of infectious disease control are seriously jeopardised by the spread of antimicrobial resistance, with extensively drug-resistant tuberculosis (XDR-TB) now a cause of great concern. Drug resistance is also evident in diarrhoeal diseases, hospital-acquired infections, malaria, meningitis, respiratory tract infections, and sexually transmitted infections, and is emerging in HIV.
HIV/AIDS is the biggest 'new disease' in terms of extent and impact. How do these new diseases arise? The BBC has given a fascinating rendition of the origin of HIV/AIDS as reported by "viral archaeologists" in the journal Science. The origin of the AIDS pandemic had been traced to the city of Kinshasa in what is now the Democratic Republic of Congo and back to the 1920s when a perfect storm of population growth, sex and railways allowed HIV to spread.
But how HIV got into humans and how it originated as a new virus is another story.
The report says a roaring sex trade, rapid population growth, and unsterilised needles used in clinics probably spread the virus.
Railways built by the Belgian colonial masters had one million people passing through the city each year, taking the virus to neighbouring regions.
But it wasn't until the 1980s that HIV was identified and came to global attention. Why the long gap before the virus left Africa and achieved pandemic proportions is not very well explained. Since the pandemic started, HIV has infected 78 million people, killing 39 million.
It is believed that HIV is a mutated version of a chimpanzee virus, known as simian immunodeficiency virus, which probably made the chimpanzee-to-human cross-species jump through contact with infected blood while handling bush meat.
Ebola virus disease (EVD) first appeared in 1976 in two simultaneous outbreaks in Sudan and the Democratic Republic of Congo. The Congo outbreak occurred in a village near the Ebola River, from which the disease was named.
But where did this virus come from, and how did it get into humans? Fruit bats have been implicated. It is thought, the WHO says, that fruit bats are natural Ebola virus hosts. Ebola is introduced into the human population through close contact with the blood, secretions, organs or other bodily fluids of infected animals such as chimpanzees, gorillas, fruit bats, monkeys, forest antelope and porcupines found ill or dead in the rainforest. Ebola then spreads through human-to-human transmission via direct contact with the blood, secretions, organs or other bodily fluids of infected people, and with surfaces and materials contaminated with these fluids.
National Geographic defers. "Fruit bats," the magazine said, "have often been touted as suspects, but the virus' reservoir host has never been positively identified. The gold standard of proof - culturing live virus from the tissues or blood of a candidate animal - hasn't ever been achieved from fruit bats, nor from any other creature. So, the virus is still at large, its reservoir indeterminate, its whereabouts unknown, somewhere within the landscape of tropical Africa."
And this 'unknown' is true for most of the new microbial diseases rushing at us. What is certain is that a combination of factors, including humans messing with the environment, is throwing up new diseases at an unprecedented rate and these can be quickly spread around the world by mass travel and trade. Many old infectious diseases, like TB, are rebounding with frighteningly resistant new strains. Vectors, too, like mosquitoes, are developing resistance to insecticides. No vector has ever been eliminated.
The country came down hard on the poor minister of health, Dr Fenton Ferguson, for his (mis)handling of chikungunya. In that civic consultation in Mandela Park on World Mosquito Day, the minister was bravely talking up the Preparedness and Response Plan for ZIKV and what we were going to do to those carrier mosquitoes.
But, let us brace for very difficult times ahead as the whole world faces an unprecedented threat of new infectious diseases and re-emergent old ones. When you listen to the WHO and the CDC, the apocalyptic harbingers don't seem so incredible after all.