A Biological Potpourri:
An Overview of Some Evolving Biohazardous Threat Agents and Global Health
Written by Frank Rando
CBRNE - Protective & Biomedical Countermeasures, University of Arizona
Collectively, infectious diseases have proven to be global scourges and the single most important contributor to human suffering, morbidity and mortality throughout various periods of history. From ancient B.C ,throughout the Middle Ages to Victorian times to the present day, the lethality of various microorganisms has touched the most primitive tribes to the most sophisticated urban dwellers. Low and middle income countries (LMICs), ie. "developing nations” continue to suffer the brunt and burden of both common and exotic pathogens usually exacerbated by malnutrition, lack of access to healthcare, inadequate public health infrastructure and extremely poor sanitary conditions.
Geopolitical factors, armed conflicts and civil strife have further exacerbated the health threats to these societies by generating complex humanitarian emergencies throughout several areas of the world. Many of the world’s LMICs suffer with severe conditions of impoverishment and stark health disparities when compared to wealthy ,industrialized nation-states. Sociocultural factors, such as ritualistic behaviors and practices, exotic food habits, religious beliefs and folklore often are contributory factors to the evolution of infectious disease outbreaks, such as HIV/AIDS and Ebola viral hemorrhagic fever in Africa.
Climate change, deforestation, and biodiversity losses are intimately connected with the propagation of disease vectors such as mosquitoes and rodent populations. Zoonotic diseases which result from trans-species “jumps” from animals to humans are among those infectious diseases facilitated by sociocultural and environmental changes.
The impact of human activities such as agriculture can have serious implications for both global animal and human health, as the two are inextricably intertwined and co-dependent. We see this in genetic reassortment associated with highly pathogenic avian influenza (HPAI) and with the emergence of various pathogens like the Filoviruses (eg. Ebola strains) and the Coronaviruses which cause Middle Eastern Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS).
In Filovirus infections, we see simian primates (monkeys) able to transmit to human primates and then direct human-to-human transmission. In the SARS-CoV outbreak, civets in China were named as the primary culprits ,and in MERS-CoV, camels served as the animal reservoir of infection capable of transmission to humans.
The dual dangers of the Hendra and Nipah viruses, which are highly pathogenic paramyxoviruses (genus Henipavirus, family of Paramyxoviridae) capable of causing severe animal and human disease are in the forefront of infectious disease epidemiology and global public health preparedness efforts.
Henipavirus infections were first reported in the 1990s causing severe and often fatal outbreaks in domestic animals and humans in Southeast Asia and Australia . Nipah virus infections were observed in vivo in humans in Bangladesh, India and Malaysia, where pigs were also infected. Hendra virus infections occurred in horses in the northeastern regions of Australia, with singular transmission events to humans. Flying foxes and fruit bats appear to be the mammalian contributors to the chain of infection associated with these viruses.
Hendra and Nipah viruses possess unique genetic characteristics, high virulence and wide host-agent interactions and are designated Biosafety Level 4 (BSL4) pathogens. Infection takes place across a wide range of mammals ranging from flying foxes to horses, pigs, cats, dogs, and humans.
Widespread infection via trans-species jumps is of concern whether it is a natural or intentional biowarfare or bioterrorism event, as it can devastate herds of livestock ,as well as cause lethal human disease. The U.S. Center for Disease Control and Prevention categorizes these pathogens as “select agents” with weaponization potential, similar to other emerging pathogens such as the Filoviruses and Orthopox viruses eg. Variola (smallpox). They prefer to grow on arterial endothelial cells rather than venous endothelial cells and also express themselves on neurons in brain tissue resulting in the occurrence of viral encephalitis in humans.
In addition , anthropogenic influences can result in the deterioration of ecosystem health resulting in environmental conditions that promote the growth of pathogens ( eg.,Vibrio and other water-borne diseases) or other organisms, such as toxic algal blooms /toxic dinoflagellates ( ie. "red tides”) which generate and release very powerful toxins harmful to animal species and humans. Toxic algal blooms consist of red tides, blue-green algae and cyanobacteria have severe impacts on human health, aquatic ecosystems and economic security.
Biotoxins most closely associated with toxic algal blooms similar to the episodes in Florida, Australia, Africa and other global regions include microcystins, anatoxin-a, paralytic shellfish toxins (saxitoxins), lyngbyatoxins and cylindrosperopsin to name several. These biotoxins can generate a plethora of adverse human health effects ranging from allergic responses to severe neurotoxicity and hepatic (liver) toxicity and organ failure in major organ systems.
These toxins along with ricin, botulinum toxin, T-2 mycotoxins (fungal toxins) can also be weaponized as biochemical warfare agents or as biologically-derived weapons of terror.
The potential for biowarfare or bioterrorism utilizing emerging pathogens and toxins is definitely there. Even parasitic diseases that are endemic to LMICs ,such as helminthic infections (worms) can be used to effectively cause parasitic illnesses among targeted populations.
The tools and methods of public health are essential in preparedness and response to a wide range of biohazardous threat agents. Biomedical research into medical countermeasures for novel and exotic pathogens and biotoxins is also critical to global public health efforts.
In conclusion, continued and enhanced global surveillance capabilities utilizing a varied array of epidemiological tools and methods, global public health education and empowerment, robust public health infrastructure, access to adequate preventive services and medical care, vastly improved environmental sanitation and addressing biopsychosocial and sociocultural factors are all needed to address these rapidly emerging health threats of the 21st Century and beyond.