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[Arthropodan vectors of human parasites: their pathology and defence reactions (author's transl)]
Abstract:
Many infectious diseases of man are transmitted by arthropods. It is not known whether the carriers were primarily susceptible or insusceptible as the cycle first came into existence. Similarly so little is understood, why some arthropods are suitable vectors and other close relatives are not suitable. Only the hypothesis that the agents are original parasites and not at all commensals or symbionts can reasonably explain the evolution of the cycles. It is shown by means of numerous examples how the vector can be damaged by the parasite. Some organs of the vector might become unfunctional, the reproduction rate might be lowered and the vector itself may die. On the other hand the vector has at its disposal defence mechanisms which are according to our present point of view limited to the midgut barrier and the hemolymph reactions. Both components of the system, the vector and the parasite together are capable of change under the influence of the other. For example through the high mortality of the susceptible part of a vector population the resistant and the tolerant individuals will be selected. On the contrary harmful parasites cannot transmit their genetic information when their virulence is so high that the vector will suffer death. Due to this the parasites succumb to a selection pressure and only the careful treatment of the vector is rewarding. Besides this rough pattern of actions and reactions exists also the possibility of developing finer adjustments, with the "molecular mimikry" as a well known example.
Insights
The evolution of infectious disease transmission cycles between arthropod vectors and parasites is driven by their co-evolutionary relationship. This dynamic interaction shapes both vector susceptibility and parasite virulence, influencing disease spread.
Area of Science:
- Vector-borne diseases
- Parasitology
- Evolutionary biology
Background:
- Arthropod-borne infectious diseases are significant global health concerns.
- The evolutionary origins and specificity of arthropod-parasite interactions remain poorly understood.
- Understanding these dynamics is crucial for controlling disease transmission.
Purpose of the Study:
- To explore the evolutionary hypothesis explaining the origin of arthropod-parasite cycles.
- To investigate the reciprocal impacts of parasites on vectors and vice versa.
- To elucidate the mechanisms driving vector competence and parasite adaptation.
Main Methods:
- Analysis of existing literature and case studies on arthropod-parasite interactions.
- Hypothetical modeling of co-evolutionary dynamics.
- Examination of vector defense mechanisms and parasite virulence factors.
Main Results:
- Parasitism can negatively impact vector fitness, affecting organ function, reproduction, and survival.
- Vectors possess defense mechanisms, including midgut barriers and hemolymph responses.
- Co-evolutionary pressures lead to selection for resistant vectors and less virulent parasites, or vice versa.
Conclusions:
- The parasite-host hypothesis provides a framework for understanding the evolution of vector-borne disease cycles.
- Reciprocal selection pressures shape the intricate relationship between arthropod vectors and parasites.
- Fine-tuned adaptations, such as molecular mimicry, further modulate these interactions.