Climate adaptation impacting parasitic infection.

The steady and ongoing change in climatic patterns across the globe is triggering a cascade of climate-adaptive phenomena, both genetic and behavioral in parasites, and influencing the host-pathogen-transmission triangle. Parasite and vector traits are now heavily influenced due to increasing temperature that almost dissolved geospatial boundaries and impacted the basic reproductive number of parasites. As consequence, continents unknown to some parasites are experiencing altered distribution and abundance of new and emerging parasites that are developing into a newer epidemiological model. These are posing a burden to healthcare and higher disease prevalence. This calls for multidisciplinary actions focusing on One Health to improve and innovate in areas of detection, reporting, and medical countermeasures to combat the growing threat of parasite emergence owing to climate adaptations for better public health outcomes. Copyright:

BACKGROUND

Climate change currently is the most pressing borderless global emergency for humanity. From the preindustrial era of the 1880s, the world is now about 1.1°C warmer with detrimental effects visible across all sectors.[1] Global efforts including climate plans and actions are now focused on reducing carbon footprints to keep the global temperature from exceeding 1.5°C to avoid the worst fallout to a point of irreversible destruction.[2] Public health is one of the single biggest areas that has been hit hard due to climate change.[3] Climate has influenced the remarkable emergence of pathogens, their altered dispersions, and host–pathogenic behaviors that have altered the global disease landscapes. As such, outbreaks of public health concerns have become more frequent, and the world has been warned of the inevitabilities of future pandemics.[4]

Parasitic infections that were mostly regional and focused on large tropical countries are increasingly crossing geographical boundaries.[5] Such phenomenon is not only associated with the parasites themselves rather is being facilitated by the vectors who are also occupying new continents. Vector parasites are showing climate-adaptive changes including genomic adaptation, higher drug resistance, pathogenicity, and tissue tropism.[6] This is leading to a much larger global footprint of parasites where nations previously hostile to several parasites are newly emerging as hotspots.[7] From the traditional epidemiology, the world, therefore, is going through a revision where health preparedness is costing much higher for the management of the newer parasitic burdens.

Fuelling by the facts, global attention is steadily increasing to understanding parasites and the vector distributions and related infections in light of climate changes. Genomic investigations in terms of biosurveillance containing the spread and disease spillovers, understanding the mechanism of genomic adaptation to find the drug targets, and developing adequate capacity in terms of workforce and infrastructure may be faciliatory toward effective medical countermeasures. Traditional vector control strategies are also being revised and new technologies are being tested to contain the spread of vector-borne parasites. This review summarizes the current status and understates how the climate is fuelling adaptions to the vectors and parasites and their consequences on the overall disease landscape across the globe. Approaches taken toward enabling better health preparedness including novel modalities of vector controls are also discussed.

THE CONCEPT OF ONE HEALTH

In a race with time to safeguard health from climate-driven pathogen adaptations, leading to higher disease provenances, an effective response and preparedness framework needs to be required. However, considering that the phenomenon is not parasitic exclusive but rather encompasses groups of pathogens and its cross interactions with host and environment, global efforts are underway to adopt and implement strong One Health strategies.[8] Underlying strategies of One Health stem from understanding the factors influencing pathogens spillover due to environmental stresses, including climate change, ecosystem disturbances, and habitat loss, that are pushing pathogens toward nutritional stress and compelling them to jump from environment to human via animal hosts by crossing the spatiotemporal barriers and immunological checkpoints.[9] As such, One Health essentially focuses on collective actions in multisectoral and multidisciplinary collaborations to work on elements of cross-sectorial factors at the interface of human, animal, and environmental health, leading to disease outcomes, including the pathogen spillover, genetics, and clinical features.[10]

WHO, OIE, FAO, and CDC are working collectively at regional levels on the concept. A preparedness framework to enable timely and efficient response against disease outbreak have been developed. The framework involves strategies for disease surveillance, laboratory assessments, capacity building, reporting and risk communications, and policy directives [Figure 1].

Figure 1

Road toward better disease response and preparedness framework

CLIMATE ADAPTATIONS IN PARASITES, IMPACT, AND CONSEQUENCES

From the adaptations triggered by evolutionary dynamics, the climate has introduced an unexpected spike in stress. To cope up (adapt) within shorter generations, both intrinsic (genetic, structural, behavioral, and physiological) and extrinsic (ecological stability, interaction with hosts and vectors, etc.) adaptations have taken place.[11] These have resulted in a cascade of changes including altered host specificity through changes in host–pathogen interaction, niche widening, and host switching. Genomic plasticity, transgenerational effects, and tissue tropism are creating new hybrids, have impacted the basic reproductive numbers, and facilitate higher tolerance to drugs.[12] Recent evidence is strong on the developing of new hybrids. For example, Trypanosoma cruzi discrete typing units III and IV are a result of intraspecific hybridization. Even during the developmental phases, the climate is triggering direct or indirect effects that are facilitating parasites to evolve more stress-tolerant.[11] These have influenced parasites to disperse to newer geography with higher pathogenicity and altered speciation.

Across the world, research footprints on under impact of climate change on parasites are expanding.[13] Most of the research has been carried out to understand the climate adaptations in malarial vectors and parasites.[14] It has been observed that increasing temperature is remarkably increasing the vectorial capacities and transmission cycles.[15] Mosquito vectors previously reported to transmit malaria mostly in the months between May and July have also shown the ability to transmit during July–September in a warmer region with a higher transmission index. Irrespective of the period of the year, malarial parasites also expressed higher thermotolerance. These have resulted in nations of the global north reporting higher incidences of malaria that initially was a concern for the global south, especially those sitting in temperate zones. In addition to malaria, other mosquito-borne parasitic infections including lymphatic filariasis are also expanding similarly.

Much similar evidence has been accumulated in climate adaptations in parasitic worms where hints toward global “worming” are very prominent.[16] Soil-transmitted helminth infections, especially ancylostomiasis and ascariasis, have dominated Africa and Asia, respectively. In contrast, Africa is witnessing a remarkable reduction of schistosomiasis because of altered distribution and lowering the abundance of the intermediate host snails.[17]

AREAS OF IMPROVEMENT

Despite the global call to improve and strengthen areas of One Health, reflection through actions is regionally dispersed and varies at local and national levels. There is a greater disparity in actions between lower- and middle-income countries (LMICs) than that of developed nations. However, considering the threat is dissolving boundaries, such disparity effectively pressurizes the well-prepared nations by transferring the burden of diseases and the related threat from less-prepared nations. Realizing such communication, coordination, and collaboration would be most required among nations in multidisciplinary and multisectoral approaches. All these would help share resources, best practices, and capacity building that collectively improves and strengthens One Health of the globe.

Disease preparedness is the key to containment. Considering that the footprints of the parasites are increasing globally and that too there are reports of emerging and re-emerging pathogens, accurate and timely detection of the pathogens through enabling better surveillance strategies following novel diagnostics modalities need to be required.[18] In realization, diagnostics modalities have been investigated for a very long time and each new development is attempting to higher sensitivity and specificity in pathogen detections at the point of care and field levels.

For the diagnosis of parasitic infections, mostly, the morphometric and serological continue to be the major approaches for the LMICs; hence, higher adoption of more sensitive molecular tools will be required. The major hurdle for LMICs is their inability to afford and sustain high-cost equipment, laboratory facilities, and retention of the workforce. It has limited use of molecular diagnostics for pathogen surveillance including those of parasites.

However, the research and development landscape in molecular diagnosis is quite promising. The ability of molecular tools to identify cryptic species, mixed infection, and submicroscopic parasite concentrations can potentially boost surveillance strategies. Several real-time tools and kits have been developed for laboratory use.[1920] Emerging tools such as direct PCR, LAMP, and chip-based platform technologies offer rapid diagnosis with excellent specificity and sensitivity.[21] In view, integration of molecular diagnostics in patient care would be very much rewarding wherein some strategies of incentivization would be required for LMICs.

Currently, genomic (molecular) investigations are also showing higher promises to shed light on the structure–function relationship of the changes and implications on pathogenesis to develop better countermeasures.[22] In this direction, many groups including ours have been working on pathogenic protein (Gal/GalNAc lectin) of Entamoeba dispar with Entamoeba histolytica by in silico analysis.[23] The information regarding the three-dimensional structure of the protein wherein such findings have explained the pathogenicity and provided a greater molecular insight into the species making way to develop novel therapeutics.

One of the biggest developments toward disease preparedness is the global attention to evolving novel strategies for vector control. The research has been focused on mosquito control programs globally where some novel strategies have gone through regulatory appraisals for safety assessments. Such technologies that are deviant from classical chemical control of vectors rely on novel biological or biotechnological interventions. In biological methods, attempts were made to develop cytoplasmic incompatibility by incorporating Wolbachia sp. into a vector (e.g., Anopheles stephansai) that result in population suppression or replacement following reproductive isolation.[24]

More recently, the advent of CRISPR-Cas as a promising tool for genome editing has facilitated the development of gene-edited mosquitoes that are incapable of disease transmission. Successful field trials with these mosquitoes, when released in nature, resulted in the transfer of edited genes into the wild mosquitoes by a process called gene drive.[25] As consequence, it resulted in population replacement through introgression of the entire drive elements into the offspring that are incapable of disease transmission.[26]

CONCLUSION

With the continuing carbon footprints due to anthropogenic activities, we are approaching irreversible climate change, and there will be the inevitability of global adaptations in pathogens including parasites. As such, the traditional knowledge of infections and immunity will see drastic revisions where the account of environmental changes at the interface of human–animal and environment in a One Health approach will be highly necessary to manage the rising global health threat. In that direction, course corrections need to be required to accommodate new technologies including genomics for a better understanding of disease dynamics and deploying efficient surveillances strategies. Multisectoral and multidisciplinary collaborations need to be facilitated to engage in more rationale sharing, capacity building, and decision-making. In line with the global efforts, attempts to be made for better health outcome at healthcare ecosystem at local as well as regional level. In this arena, groups/organizations contributing to the cause of parasitology need to play an instrumental role including promotion and incentivization of research, development, and capacity building [Figure 2].

Figure 2

Role of organizations for the promotion and advancement of parasitology capacity building

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.