Abortive long-lasting sporogony of two Haemoproteus species (Haemosporida, Haemoproteidae) in the mosquito Ochlerotatus cantans, with perspectives on haemosporidian vector research

Abstract

Haemoproteus spp. are cosmopolitan vector-born haemosporidian parasites, some species of which cause diseases in non-adapted birds. Recent polymerase chain reaction (PCR)-based studies have detected mitochondrial cytochrome b gene lineages of these Haemoproteus parasites in blood-sucking mosquitoes and speculated about possible involvement of these insects in transmission of avian haemoproteids. However, development of Haemoproteus lineages has not been documented in mosquitoes. We infected 304 individuals of Ochlerotatus cantans, a widespread Eurasian mosquito, with Haemoproteus tartakovskyi (lineage hSISKIN1) and Haemoproteus balmorali (lineage hROBIN1). Mosquitoes were allowed to take non-infected and infected blood meals and maintained in the laboratory until 17 days post-infection (dpi). They were tested for presence of sporogonic stages by microscopic and PCR-based methods. Microscopic examination revealed partial development of both parasites in the infected insects. Numerous ookinetes were seen in the gut area and adjacent tissues located in the head, thorax and abdomen of mosquitoes between 1 and 5 dpi. Numerous oocysts were seen in the midgut wall between 4 and 15 dpi; they were also present in the head and thorax of infected mosquitoes testifying to the active movement of ookinetes throughout the body. Oocysts degenerated between 11 and 17 dpi. Sporozoites were not seen in oocysts or mosquito salivary glands, indicating abortive sporogonic development at the oocyst stage. In accordance with microscopy data, PCR and sequencing revealed presence of the lineages hSISKIN1 and hROBIN1 in experimental mosquitoes as long as 15 and 17 dpi, respectively, demonstrating relatively long survival of Haemoproteus parasites in the resistant insects without DNA degeneration. The present study shows that PCR-based diagnostics should be carefully used in vector studies of haemosporidians because it detects parasites in insects for several weeks after initial infection, but does not distinguish abortive parasite development. Demonstration of infective sporozoites in insects is essential for definitively demonstrating the insects are vectors.

Different meal, same flavor: cospeciation and host switching of haemosporidian parasites in some non-passerine birds

“…Moreover, phylogenetically related haemosporidian lineages (e.g., sister lineages) do not necessarily have a similar host breadth and geographic distribution [74], which challenges our ability to predict novel haemosporidian zoonoses. Taken together, the evidence on host distributions suggests that haemosporidian parasites have the potential to rapidly develop novel host-associations [19], but see [64]. …”

“…Recent work on Culicidae [57-59] and Ceratopogonidae [18,19,60,61] shows that many vector species have broad feeding preferences, even across vertebrate classes. Thus, vectors may come in contact with a diverse array of Haemosporida parasites, including genera they do not normally transmit [e.g., [18,60,62-64]. The fact that many vector species have broad vertebrate host preferences and are susceptible to infections by different Haemosporida genera, would suggest that specificities of both vertebrate and insect host immune systems would mediate parasite “jumps” across distantly related avian hosts [see [15,64].…”

“…Thus, vectors may come in contact with a diverse array of Haemosporida parasites, including genera they do not normally transmit [e.g., [18,60,62-64]. The fact that many vector species have broad vertebrate host preferences and are susceptible to infections by different Haemosporida genera, would suggest that specificities of both vertebrate and insect host immune systems would mediate parasite “jumps” across distantly related avian hosts [see [15,64]. Experimental studies have demonstrated that an avian parasite, Plasmodium lophurae , can adapt to and be viable in mice after just four rounds of infectious inoculations [65].…”

Genetic diversity of avian haemosporidians in Malaysia: Cytochrome b lineages of the genera Plasmodium and Haemoproteus (Haemosporida) from Selangor

“…The registration of gametocytes in the blood films demonstrates that these bird individuals are susceptible to certain haemosporidian infections and that parasites can be transmitted . Previous studies indicate that infections are sometimes abortive, causing incomplete development of parasites in both birds and insects (Olias et al, 2011;Palmer et al, 2013;Valki unas et al, 2013). That is why it is essential to combine molecular-based surveys with microscopy for detecting haemosporidian infections.…”

Description, molecular characterisation, diagnostics and life cycle of Plasmodium elongatum (lineage pERIRUB01), the virulent avian malaria parasite

“…Sporogonic development during the oocyst stage may be critical for successful sporogony. There are data about encapsulation and melanization of oocysts in midguts of mosquitoes infected both with Plasmodium and Haemoproteus parasites (Collins et al, 1986;Schwartz and Koella, 2002;Dimopoulos, 2003;Sinden et al, 2004;Valkiūnas et al, 2013;Palinauskas et al, 2015). This defence mechanism is often recorded because it can be readily visualised in midgut preparations.…”