For instance, increased biting rate that increases the infectious agent’s transmission probability may not improve the vector’s fitness. Similarly, few studies have documented whether infectious agents alter the fitness of the arthropod host by manipulating its behaviour. However, whether these behavioural changes due to infection are a result of direct manipulation by the infectious agent leading to its transmission advantage is not determined for the for the numerous vector and pathogen species recorded. Infections with many pathogens can modulate different behavioural traits of their arthropod hosts.

This may be due to the adaptation and long co-evolution of vectors and pathogens. Although vector-borne pathogens cause disease in vertebrate hosts during their life cycles, there is no overt disease in vectors. For an infectious agent, being proficient requires it to be transmitted to susceptible hosts. For an arthropod, being a competent vector means being capable of attaining, sustaining, and transmitting a pathogen, such as a virus. These can include cellular interactions leading to molecular changes in the vector or interactions leading to changes in pathogen transmission. Studies of the interactions between vectors and their pathogens are vital to understanding vector-borne disease transmission and epidemiology. Other vector-borne diseases such as leishmaniasis, schistosomiasis, and Chagas disease also infect hundreds of millions of people worldwide, causing high morbidity and mortality. For viral infections, dengue is the most prevalent, with an estimated 390 million infections worldwide and around 20,000 deaths per annum. Malaria causes an estimated 220 million cases globally and leads to more than 400,000 deaths yearly, with children under the age of 5 years being the most vulnerable group. Mosquito-borne diseases are the deadliest diseases among all vector-borne diseases (World Health Organisation, 2015), while tick-borne diseases are the most rapidly spreading diseases (World Health Organisation, 2017). According to the World Health Organisation (WHO), annually over 700,000 deaths are caused by vector-borne diseases, including malaria, dengue, yellow fever, and Japanese encephalitis. Vector-borne diseases are caused by bacteria, viruses, or parasites and are spread by vectors between susceptible hosts including wildlife, domestic animals, and humans. This study will not only help in understanding virus–vector interactions but will also benefit in establishing role of these behavioural changes in improved epidemiological models and in devising new vector management strategies. Although some of these behavioural changes may theoretically increase transmission potential of the pathogens, their effect on the disease epidemiology remains to be verified.

The research has shown that infection with pathogens alter the mosquito’s flight activity, mating, fecundity, host-seeking, blood-feeding, and adaptations to insecticide bed nets, and similarly modify the tick’s locomotion, questing heights, vertical and horizontal walks, tendency to overcome obstacles, and host-seeking ability. Here, we review relevant publications to assess how pathogens modulate the behaviour of mosquitoes and ticks, major vectors for human diseases. Several studies have shown that infection with pathogens can alter these behavioural traits of the arthropod vector. Vector behavioural traits, such as fitness, host-seeking, and host-feeding, are key determinants of vectorial capacity, pathogen transmission, and epidemiology of the vector-borne disease.

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