It is reported that the biting pattern of mosquitoes happens in a manner and time when plasmodium parasites are feeding on the host blood and the reason given is that that helps to transmit the parasite from one host to another. But the causal relationship if any is not known.
Could you define your question more carefully please? Who reported what? Which Plasmodium species? Which mosquito species? And which stage of the parasite are you talking about - for transmission this would be gametocytes, or are you referring to schizogony/ring stages in the peripheral blood?
P. falciparum stage V (mature) gametocytes circulate in the peripheral blood for a few days ie there is no evidence that they might hide away during the day once they are released into the peripheral blood. However peak densities do appear to have a diurnal pattern but this was not reported to coincide with the peak biting time of the main Anopheles species in the area of the study "Observations on the periodicity of Plasmodium falciparum gametocytes in natural human infections" by Magesa SM, Mdira YK, Akida JA, Bygbjerg IC, Jakobsen PH. Acta Trop. 2000 Oct 2;76(3):239-46. See also Hawking et al 1970 Evidence for cyclic development and short-lived maturity in the gametocytes of Plasmodium falciparum Trans. R. Soc. Trop. Med. Hyg., 65 (1971), pp. 549–559.
A study by a colleague of mine, data yet to be published show that in Ghana the biting pattern of female anopheles mosquitoes coincide with the appearance of the gametocytes of P. malariae, falciparum. I suggested to him that his observation smacks of a kind of co-evolution between the parasites and the vector or at worst it could be mere coincidence
Alex, it would be interesting to know what does the "coinciding" means / defined in your friend´s study. As Lisa, rightly mentioned that the pf gametocytes would circulate in the blood for a few days. would any bite during this time be called ²coninciding² then ?
Khalid, the answer to your question is no. According to my colleague's study 'coincidence' was determined by counting the number of female anopheles bite at a particular period and then taking blood samples of volunteers at that time to determine parasitemia. He found high parasitemia correlated with high number of female anopheles bites.
when the female Anaphalese mosquito bites a patient infected with any of the 4 human malarial parasites, the male and female gametocytes of the parasite present in the blood also are sucked. in the midgut of the mosquito further sexual multiplication occrs resulting in production of plenty of SPOROZOITES. these sporozoites accumalate in the mouth of the mosquito. when it bites another person for its blood meal, it has to empty the blocked mouth part, thus it discharges the sporozoite in the mouth into the peripheral blood of the second person. thus the cycle of malaria is maintained
That's not quite right Vijay. Male and female gametes fuse in the midgut to form the zygote (sexual reproduction) but then sporozoites are formed by mitotic division (asexual). The sporozoites move in the haemolymph (blood) of the mosquito to the salivary galnds of the mosquito, where they invade the epithelial wall of the gland and end up in the salivary ducts. So the sporozoites are in the salivary glands of the mosquito, not in the mouth (mosquitoes of course don't really have a mouth, they have a feeding tube called a proboscis).
During bloodfeeding, the mosquito inserts its proboscis into the host and injects saliva first, and the sporozoites pass in with that, and then the mosquito takes the blood up into the gut.
But this doesn;t really explain the original question asked by Alex.
Lisa and Vijay i do appreciate your help; i think that is the beauty of science in that scientists must at some point disagree to agree or have consensus on a problem. Like Lisa rightly intimated, i only asked for an answer to why plasmodium parasite distribution in peripheral blood seem to coincide with vector (Female infected anopheles mosquito) feeding behaviour, But i ended up getting extra information on the parasite life cycle. Its all good.
Hi Alex. The reference below addresses the subject that you are asking about:
Magesa SM, Mdira YK, Akida JA, Bygbjerg IC, Jakobsen PH. 2000. Observations on the periodicity of Plasmodium falciparum gametocytes in natural human infections. Acta Trop. 76(3):239-46.
However, it appears from this study that the circadian periodicity of Plasmodium falciparum gametocytes in peripheral blood did not coincide with the biting periodicity of the local population of Anopheles gambiae.
Furthermore, a study of the infectivity of Plasmodium falciparum to Anopheles gambiae seems to show that this is aperiodic:
Githeko AK, Brandling-Bennett AD, Beier M, Mbogo CM, Atieli FK, Owaga ML, Juma F, Collins FH. 1993. Confirmation that Plasmodium falciparum has aperiodic infectivity to Anopheles gambiae. Med Vet Entomol. 7(4):373-6.
So the function of the circadian periodicity of Plasmodium falciparum gametocytes has yet to be determined.
Like for sub-periodic filariasis, it seems that gametocytes of Plasmodium falciparum undergo double out-of-phase circadian biorhythms :
Out-of-phase circadian biorhythms in gametocytes of Plasmodium falciparum
Gaston Pichon, Abdoulaye Guèye, Jean-François Trape, Christian Boudin, 2014.
The transmission of malaria by mosquitoes is accidental. The mosquitoes do not choose the patients based on the infection with malaria paraistes. The interesting bionomic behavior of the mosquitoes is that the different species do not compete for blood meals at the same time. For ex anophles are early night feeders and culex are late night feeders. I am of the opinion that , neither the paraites have intentions to be transmitted The parasites [malaria] are in the circulation during the infection and get transmitted by the vectors, which may be also accidental. Interesting but need to be tested [very difficult]. thanks for raising a question with curiosity. lalitha kabilan.
Hi Lalitha. The mosquito vectors of malaria have likely evolved their blood feeding periodicity to optimise their chances of obtaining a blood meal from their preferred host(s). I think the question is more about whether, through co-evolution of the mosquito-malaria parasite relationship, the parasite has evolved a similar periodicity to optimise its chances of being taken up in a blood meal to infect the mosquito.
As far as I know there is no solid answer and I think its a chance happening the probabilty of which depends on level of intensity of transmission and the endemicity in the area. The infective forms are the sporozoites which are present in the salivary glands of the mosquito. If it so happens that the blood meal contains gametocytes then the cycle of transmission will be maintained. Any way it is an area which needs researching- may be to study whether infected mosquitos are more voracious blood feeders or not when compared to non- infected ones !!??
Ahmed A. Mohamedani
I thing that during the biting of mosquitoes, there is the transmission of spororoites to the hepatocytes through the blood of human, but this steps requires certain time to infect red blood cells.
This is becoming an interesting discussion. Another question to broaden the discussion. While feeding, does Anopheles releases a"chemical" which trigger the appearance of gametocytes in the peripheral blood of the host?
Alex. As i think that there is some connection between peak biting time and parasite presence in peripheral blood as the Nature has given a perfect cycle for each living organism to survive in environment.
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