Introduction

Overview

About 3.6 billion individuals live in places predisposed to climate change hazards shortly. Populations mostly affected are developing countries that have less ability to withstand these changes.¹ Causes of climate change could be natural or due to human activities. Natural causes include volcano eruptions or changes in the activities of the sun. Human activities which cause more than 80% of these climate changes include

• Burning of fossil fuels to generate electricity and manufacturing industrial goods. This emits carbon-dioxide and nitrous oxide which are known as the greenhouse gases. These gases surround the earth trapping heat from the sun² 
• Carbon-di-oxide gas emission due to  deforestation² 
• Road Vehicles(cars, trucks) as well as ships and planes emit carbon-dioxide due to the usage of fossil fuel for energy^2,3 
• Food production using fertilizers produces nitrous oxides thus causing the greenhouse effect^2,3 
• Production of methane which is a greenhouse gas by animal livestock like cows and sheep during digestion³ 

Consequences of climate change include

• Natural consequences: high temperatures, droughts, floods, unclean water, soil degradation etc⁴
• Social and health consequences: infections and disease spread, increased summer heat and winter cold-related deaths etc⁴

Climate change and parasitic diseases 

Among the many consequences of Climate change, parasite growth, development and spread are among the affected health consequences leading to increased parasitic diseases.

An increase in temperature promotes the growth of arthropod vectors that carry and spread parasites.

Deforestation promotes the spread of parasites as their habitat has been destroyed, giving room for other species to inhabit this newly freed-up area.⁵ 

Human activities like migration, transportation, habitations and settlements cause climate changes through fossil fuel consumption producing green gas effects. This leads to warmer temperatures which is favourable for parasite transmission.⁵ 

Understanding parasitic diseases

Definition of parasitic diseases

Parasitic Diseases are infections caused by parasites, which are microorganisms that live and reproduce in another organism. The other organism is called the host. The parasites lives off nutrients from the host to grow and develop.⁶

Types of parasites 

There are three types of parasites causing diseases in humans: Protozoa, helminths, and ectoparasites.

Protozoa are single-cell parasites having a cell membrane, nucleus and cytoplasm, causing infections in humans that could be asymptomatic, as well as life-threatening infections. They exist in two stages: 

• Trophozoite stage which is the stage at which reproduction takes place
• Cyst stage which is the dormant stage

Examples include:

• Plasmodium Species which causes malaria infections
• Entameoba hystolitica which causes amebiasis
• Toxoplasma gondii which causes toxoplasmosis infection
• Giardia intestinalis which causes giardiasis infection etc⁶ 

Helminths, also known as parasitic worms, are multiple-cell organisms with complex tissues and organs. They are grouped into roundworms(Nematoda) and flatworms (platyhelminthes). Flatworms are further divided into tapeworms(cestodes) and fluke worms (trematodes). Examples include

• Ancylostoma duodenalis which causes intestinal hookworm infection
• Necantor americanus also causes intestinal hookworm infections
• Ascaris lumbricoides which causes ascariasis.
• Onchocerca volvulus that causes onchocerciasis commonly known as river blindness

Ectoparasites are micro-organisms whose habitation is on external surfaces of their host. They include ticks, parasitic flies, lice, fleas and mites. They cause a group of diseases known as epidermal parasitic skin diseases.⁷  

Transmission method

Parasites are transmitted through the following methods.

• Animals(pets, animal farming) to humans for zoonotic parasites
• Water through parasite contamination
• Blood through blood transfusions, needle accidents for bloodborne parasites
• Food through eating of undercooked meat or fish or crab, contaminated vegetables with human or animal feaces, raw seafood
• Insects through insect bites for vector borne infections⁸
• Soil contamination as seen in cases of soil transmitted helminths⁸

Temperature changes impact on parasitic diseases

Temperature changes have a direct and indirect impacts on parasitic diseases occurrence and spread. Temperature increase directly

• Increase the vector transmission and infection rates due to increased feeding rates of vectors⁹ Plasmodium parasite is an example which proliferates in warmer temperatures¹⁰
• Promotes growth of insects and arachnids, known vectors that carry and transmit parasites in warmer climates¹⁰  

Indirectly, Increase in temperatures can lead to droughts and flooding (through the El niño phenomenon), and heatwaves, which also favour hookworm survival.

Impact of precipitation and humidity on parasitic disease

Increase precipitation is a form of transportation of water transmissible parasites. Areas with heavy rainfal and melting snow leaves stagnant water which promotes the development of insect vectors as such increases the rate of parasitic infections. Long duration of rainfall creates a humid climate is is also favorable for vector growth and development. ¹⁰ 

Schistosoma parasite species that use snails as vectors survive depending on the quantity of precipitation and duration of the dry season. Some parasites survive only in dry seasons whereas others only in humid areas.

Excessive precipitation leads to flooding which is favorable for the proliferation of hookworm as seen in haiti.¹⁰ Gao and collaborators demonstrated this phenomenon as the reason for the resurgence of the Malaria parasite in China following a period of low malaria infection.¹¹

Changes in ecosystems and habitats and its impact on parasitic diseases

Deforestation impacts parasite spread and settlement

• Replacement of cleared-up forest with farmlands to cultivate vegetables, and crops and keep animal livestock promotes the development of vectors which in turn increase the transmission rate of parasites to humans. ¹⁰
• Deforestation causes changes in soil composition and creates vast lited lands susceptible for the formation of stagnant water which favours parasitic vector habitations. The changes in soil composition causes parasitic migration of soil transmissible parasites as well.^5,10 Malaria parasite (plasmodium species), Leishmania  species adapt to ecological changes following deforestation.¹⁰ 

Impact of human migration and changing behavior on parasitic diseases

Migration and creation of new settlement areas disrupt the ecosystem and soil composition favouring migration of vectors as well leading to variations in parasitic disease rates.¹⁰ 

Transportation systems by cars, trucks, ships and planes with the usage of fossil fuels causing climate changes also impact parasitic disease spread indirectly. 

Construction of dams, roads and infrastructures without good irrigation systems favours the formation of stagnant water, causing vector growth thus increasing parasitic infection rates.¹⁰  

Adaptation and mitigation strategies to manage the impact of climate change on parasitic diseases

In order to adapt to the rapidly changing climate and its impact on parasitic diseases, adaptations and mitigation strategies have been established. There are health based strategies and Non-health based strategies.

Health based strategies

• Strengthening health systems: Training and preparing health professionals on managing parasitic diseases keeping up with the climate change variations, screening of parasitic disease for early management¹³
• Create awareness by carrying out studies to monitor the parasitic disease trends with climate change, improve surveillance and monitoring for early detection of climate and ecological changes and initiate action plan to control its effects¹⁰ 
• Public health policies established to minimize parasitic infection prevention, transmission as well as early detection and management protocols to save lives. 

Other strategies

• Reduce greenhouse gas emissions through decreased usage of fossil fuels for energy, encouraging biking and walking, and reduce usage of combustive vehicles¹²
• Promote water sanitation and hygiene to prevent ingestion of contaminated water and food thus preventing parasitic infections 
• Promote Planting of trees and reforestation to reduce carbin-dioxide in air thus reducing the greenhouse effect, maintaining soil composition and preventing the stagnation of water¹² 
• Construct improved infrastructures resilient to the effects of climate change with zero usage of fossil fuels for cooling or heating¹² 
• Climate policies are established to reduce fossil fuel usage, and pollution as well as deforestation, and encourage climate-friendly activities¹² 

Summary

Climate change that is caused mostly by human activity through consumption of fossil fuels leading to the emission of greenhouse gases is a global problem nowadays. These has a great impact in the growth and development of vectors that transmit parasites, causing increased occurrence and spread of parasitic diseases. These climate hazards include extreme temperatures, precipitation changes, humidity, ecological changes due to deforestation, habitation, other human activities like migration, transportation, settlements etc. Strategies are being established to reduce climate change hazards, adapt to the already present climate change as well as manage parasitic diseases spread and treatment.