Do Malaria Parasites Change Mosquito Host-Seeking And Biting Behaviour?

DO MALARIA PARASITES CHANGE MOSQUITO HOST-SEEKING AND BITING BEHAVIOUR?
Student ID: 2337230A
Tutor’s Name: Dr Lisa Ranford-Cartwright
Course: Host-pathogen interactions
Date: 08/01/2018
Word Count: 3531 words
Table of Contents TOC \o "1-3" \h \z \u INTROUDUCTION TO MALARIA PARASITES PAGEREF _Toc505714466 \h 3Mosquitoes as Malaria Vectors PAGEREF _Toc505714467 \h 4Host-seeking Behaviour PAGEREF _Toc505714468 \h 6Sight and Heat PAGEREF _Toc505714469 \h 7Scent PAGEREF _Toc505714470 \h 8Skin Microbiota PAGEREF _Toc505714471 \h 8Sweat PAGEREF _Toc505714472 \h 8Biting Behaviour PAGEREF _Toc505714473 \h 9How Malaria Parasites Change Mosquito Host-Seeking and Biting Behaviour? PAGEREF _Toc505714474 \h 11How the Malaria parasite in a person changes mosquitoes’ behaviour? PAGEREF _Toc505714475 \h 11How the Malaria parasite in the mosquito changes the mosquito’s behaviour? PAGEREF _Toc505714476 \h 12Conclusion PAGEREF _Toc505714477 \h 12References PAGEREF _Toc505714478 \h 14
DO MALARIA PARASITES CHANGE MOSQUITO HOST-SEEKING AND BITING BEHAVIOUR?
INTROUDUCTION TO MALARIA PARASITES
Malaria is an ailment transmitted by protozoan parasites known as Plasmodia, which are categorized in to the parasitic phylum Apicomplexa. The genus Plasmodium has over two hundred species under it (Krief et al., 2010). These can infect animal species such as some mammals, birds and/or reptiles. Of these, five species have been linked to human infections (Krief et al., 2010). These include; P. falciparum, P. vivax, P. ovale, P. knowlesi and P. malariae. The different species are found in different parts of the world.
The P. falciparum is normally located in tropical and subtropical parts especially in Africa where it predominates. The P. vivax is common in Asia, Latin America, and some areas of Africa. The P. ovale is predominant in Western Pacific Islands and the Western Africa. P. knowlesi is located all over Southeast Asia and P. malariae is found globally. This shows that Malaria is a global menace which affects most nations. The different species have varying lifecycles and different effects when they infect humans. P. falciparum causes the most severe even fatal malaria.
The natural ecosystem of malaria entails malaria parasites successfully contaminating two types of hosts: the female Anopheles mosquito and humans. Normally, humans get malaria when bitten by an infective female Anopheles mosquito. To infect someone, the female Anopheles mosquito must have been infected through biting and sucking blood from an infected person (White, 2017). The Anopheles mosquito bites an infected person and the blood it sucks contains microscopic malaria parasites. Later, when it bites its next victim, the parasites mix with the Anopheles mosquito’s saliva and this is injected in to the person being bitten.
The life cycle of the malaria parasite starts when the female Anopheles mosquito bites someone and injects the malaria parasite in to their bloodstream. These malaria parasites are transmitted in the form of sporozoites which move rapidly to the human liver where they multiply asexually for seven to ten days without causing any symptoms. The liver cells release the merozoite forms of the parasite in to the bloodstream which attack the red blood cells, multiply until the cells rupture. This process is repeated causing bodily fever whenever the parasite lyses the erythrocytes.
Some of the merozoites in the blood cells develop to gametocytes which are a sexual form. The gametocytes develop in to gametes and later in to actively moving ookinetes in the mosquito’s midgut wall and form oocysts where many sporozoites develop. When the gametocytes are picked by the female Anopheles mosquito during a blood meal, they begin another different new growth and multiplication cycle in the mosquito. After about ten to eighteen days, the sporozoites are found in the mosquito’s salivary glands (CDC, 2016). When the female Anopheles mosquito feeds on another human being, the sporozoites are injected with the mosquito’s saliva and begin another human infection once they parasitize the liver cells. Hence, the female Anopheles mosquitoes act as vectors carrying the disease from one human being to another in the course of their feeding.
This paper will fixate on the behaviours of the Anopheles mosquito in biting their hosts, factors influencing host-seeking behaviour and how these mosquitoes select their hosts. It will delineate the biting behaviour in regards to the time of day, the length of time they feed, their persistence in the biting behaviour and the size of the blood meals taken. In addition, this essay will elucidate how the malaria parasites may alter the mosquitoes’ behaviour in regards to host seeking and biting. Finally, this behaviour change will be assessed in regards to host choice and rate of feeding. This behaviour change will be evaluated when the malaria parasite is in the two hosts: the human body and in the Anopheles mosquito.
Mosquitoes as Malaria Vectors
The female mosquitoes of the genus Anopheles spread malaria among humans. The female mosquitoes require blood meals for egg production. The blood meals can come from different animals. Some mosquitoes have specific tastes while others generally feed on whatever and/or whoever. These blood meals are the connection between the human and the mosquito hosts malaria parasite life cycle. There are several factors which influence the prosperous development of the malaria parasites in the mosquito. One such crucial factor is temperature. The malaria parasites require ambient temperatures and humidity to thrive. Higher temperatures are more suitable for the growth acceleration of the parasite in the mosquito. In addition, the Anopheles must survive long enough for the parasite to finish its cycle in the mosquito host. The duration usually takes almost ten to eighteen days. Unlike the humans, the mosquito does not evidently suffer from hosting the parasites.
There are over four hundred and thirty Anopheles species and only 30 to 40 of these transmit malaria (CDC, 2016). Malaria is spread by the different Anopheles species depending on the area and the environment. Anophelines are found all around the world except in the Antarctica. All mosquitoes undergo four stages in their lifecycle. Anopheles have four life stages that include the egg, larva, pupa and lastly adult (Figure 1). It is in the final adult stage that the female Anopheles mosquitoes act as malaria vectors. The adult females have a life span of one to two weeks in nature and up to a month when in captivity (CDC, 2015). Their survival is dependent on humidity, temperature levels and on their capacity in obtaining blood meals while avoiding host protection. A mosquito’s capability in transmitting malaria depends on its inborn susceptibleness to Plasmodium, the host option and its longevity.
Figure 1. (Schematic of a mosquito lifecycle).
Host-seeking Behaviour
Host discovery behaviour by mosquitoes is highly driven by olfactory signals given off by different hosts. The ease and ability to find a host also influences their host-seeking behaviour. This means that spatial setting of a host is probable to influence the spatial distribution of the odour pride. This implies that it may be more probable for a mosquito to discover a large roost of birds than it to locate a solo bird. Cummins et al. (2012) explain that not much is known on mosquitoes’ host finding behaviours and strategies. Crosswind plume discovering most effectively leads mosquitoes to their sources of blood meals (Cummins et al., 2012). This crosswind flight strategy is most effective in a straight odour plume. Cummins et al. (2012) also established that the larger the group of hosts, the higher the per capita contact rate with the mosquitoes.
Mosquitoes also tend to have outdoor host-seeking behaviours rather than indoor-based hosts (Reddy et al., 2011). A study by the authors in Punta Europa region revealed that throughout the night, biting behaviour by An.melas and An.gambiaem was high. The researchers also established that mosquito host seeking when humans were awake especially in the morning and in the evening was high. This is attributable to the extensive indoor insecticidal interventions used by many. Human blood is especially rich in amino acids called threonine useful for the production of mosquito egg proteins. Mosquitoes use chemotrophic attraction whereby some species have higher degree of attraction than others. There are varying kairomones that mosquitoes respond to. These include; carbon dioxide, lactic acid, ammonia and other aliphatic carboxylic acids. All these perform critical roles in the mosquitoes’ host pursuing behaviour. Mosquitoes mostly use three sensory inputs to identify their targets. These include; sight, scent and heat.
Sight and Heat
Mosquitoes use sight as their second selection and detection method. Mosquitoes have compound eyes separated from each other. The eyes have many different visual units called ommatidia. Each of the ommatidia is highly light sensitive and has a lens. Hence, mosquitoes cannot clearly see details but can detect small movements. As a result, mosquitoes only see human who are only up to approximately ten metres away (Reddy et al., 2011). A study conducted on “Wolbachia-free A. ageypti” colony by Unlrich et al. (2016) revealed that there were more mosquito bites at temperatures 30-40oC compared to temperatures below that. Another study by Jones, J. C. (1978) revealed that mosquitoes can pick up human scent at distances ranging from 10-50 meters away using visual cues to find the hosts they target. Using a heated gas panel, the researchers were also able to establish that mosquitoes were attracted to heat on the human body. Even then object distinction is difficult. It is until the person is about three meters away that the mosquitoes then use their thermal receptors on the tips of their antennae to locate blood.
Scent
Mosquitoes’ olfactory systems are made up of long and about fifteen segments of antennae. These help detect host odours and even in the determination of odours of breeding sites. The mosquitoes’ antennae have varying types of setae which detect repellent odours as well as attractive odours. In terms of scent, female mosquitoes detect their hosts and hunt blood by identifying organic substances produced by the hosts (Ray, 2015). Another study by (Zwiebel & Takken, 2004) established that the olfactory system is the greatest determinant towards the ability of a mosquito to select a host. These female mosquitoes can smell carbon dioxide and lactic acid which is up to thirty-six meters away. Carbon dioxide is present in the atmosphere hence these mosquitoes mostly respond higher than usual concentrations usually when this is mixed with the host odour. The most attractive combination is a mixture of carboxylic acids, lactic acid, carbon dioxide and ammonia.
Skin Microbiota
According to Zwiebel & Takken (2004), human skin microbiota influences the attraction to malaria mosquitoes. The researchers established that the composition of the skin microbiodata played a crucial task in the productivity of human body smell. Another study conducted by Ray (2015) established that a skin that lacks sweat is odourless and attracts less mosquitoes. Skin bacteria transform non-volatile composites in to unsettled compounds owning distinctive odours. This is highly attractive to the female mosquitoes.
Mosquitoes can be attracted to high pheromone levels, perfumes, alcohol, folic acid and diseases such as hyperhidrosis. In a study by Zeng et al., 2017) found that some perfumes can easily attract mosquitoes while others can highly repel mosquitoes depending to the nature of the scent. The researchers argued their case using a perfume that was owned by Ivanka Trump. The perfume proved to be a mosquito repellent. The hyperhidrosis condition makes individuals sweat more hence such individuals are more prone to be sought by mosquitoes and be bitten. Floral scents are normally most attractive to mosquitoes. Mosquitoes are attracted to the salt, potassium and even lactic acid produced by the human body.
In addition, the blood type of an individual influences their attraction to mosquitoes. Individuals with blood group O are more likely to attract mosquitoes (CDC, 2016). In addition, people with higher body temperatures tend to be more attractive to malaria causing mosquitoes. According to a study by Yoshida et al. (2007), sick people have high affinity for being sought, detected and bitten by mosquitoes owing to higher bodily temperature from fevers. Another study by Gonçalves el al. (2017) revealed that expectant women are most attractive to mosquitoes. The researchers associated this with the fact that expectant women exhale more carbon dioxide than those who are not pregnant. In addition, they have higher body temperature and have more blood in their bodies. This means they have higher affinity to be targeted by mosquitoes. Also, people who take in more potassium and salt are highly likely to be mosquito targets.
Biting Behaviour
Mosquitoes transmit malaria in the course of their feeding by biting their hosts to consume blood from them. Mathania, Kimera and Silayo (2016) discovered through their study that the Anopheles mosquitoes are night-biting vectors of malaria. Previous studies postulated that Anopheles biting on humans usually occur in the early evenings when people are still active (Russell et al., 2011). However, mosquitoes’ species highly evolve and change their behavioural adaptations in order to survive (Sokhna, Ndiath &Rogier, 2013). The mosquitoes’ activity levels are highly dependent on the species that the mosquitoes belong to. For example, those in the genus Aedes are active during day time hence bite and feed during these times especially in early mornings and evenings (Chen et al., 2017). In another study involving 5,170 mosquitoes including aede...