Data from: The consequences of co-infections for parasite transmission in the mosquito Aedes aegypti

1)Co-infections may modify parasite transmission opportunities directly as
a consequence of interactions in the within host environment, but also
indirectly through changes in host life-history. Furthermore, host and
parasite traits are sensitive to the abiotic environment with variable
consequences for parasite transmission in co-infections. (2)We investigate
how co-infection of the mosquito Aedes aegypti with two microsporidian
parasites (Vavraia culicis and Edhazardia aedis) at two levels of larval
food availability affects parasite transmission directly, and indirectly
through effects on host traits (3)In a laboratory infection experiment we
compared how co-infection, at low and high larval food availability,
affected the probability of infection, within-host growth and the
transmission potential of each parasite, compared to single infections.
Horizontal transmission was deemed possible for both parasites when
infected hosts died harbouring horizontally-transmitting spores. Vertical
transmission was judged possible for E. aedis when infected females
emerged as adults. We also compared the total input number of spores used
to seed infections with output number, in single and co-infections for
each parasite. (4)The effects of co-infection on parasite fitness were
complex, especially for V. culicis. In low larval food conditions,
co-infection increased the chances of mosquitoes dying as larvae or pupae,
thus increasing opportunities for V. culicis’ horizontal transmission.
However, co-infection reduced larval longevity and hence time available
for V. culicis spore production. Overall there was a negative net effect
of co-infection on V. culicis whereby the number of spores produced was
less than the number used to seed infection. Co-infections also negatively
affected horizontal transmission of the more virulent parasite, E. aedis,
through reduced longevity of pre-adult hosts. However, its potential
transmission suffered less relative to V. culicis. (5)Our results show
that co-infection can negatively affect parasite transmission
opportunities, both directly as well as indirectly via effects on host
life-history. We also find that transmission is contingent on the combined
effect of the abiotic environment.

(1) 共感染（co-infection）既可通过宿主体内环境中的相互作用直接改变寄生虫的传播机会，也可通过改变宿主生活史（life-history）间接产生此类影响。此外，宿主与寄生虫的性状均对非生物环境（abiotic environment）敏感，这会对共感染情境下的寄生虫传播产生各异的影响。
(2) 本研究旨在探究：当埃及伊蚊（Aedes aegypti）在两种幼虫食物可获得性水平下，遭受两种微孢子虫（microsporidian）——Vavraia culicis与Edhazardia aedis——的共感染时，该共感染如何直接影响寄生虫的传播，以及通过调控宿主性状间接改变传播效率。
(3) 本研究通过室内感染实验，对比了低、高幼虫食物可获得性条件下，共感染与单一感染（single infection）对每种寄生虫的感染概率、宿主体内增殖水平以及传播潜力的影响差异。当感染宿主死亡且体内携带水平传播（horizontal transmission）孢子时，我们认定两种寄生虫均具备水平传播能力；当感染雌性宿主羽化为成虫时，我们判定Edhazardia aedis具备垂直传播（vertical transmission）能力。此外，本研究还对比了单一感染与共感染情境下，每种寄生虫用于接种感染的孢子总投入量与最终产出量。
(4) 共感染对寄生虫适合度（parasite fitness）的影响较为复杂，尤以V. culicis为甚。在低幼虫食物条件下，共感染提升了蚊幼虫或蛹的死亡率，从而扩大了V. culicis的水平传播机会；但与此同时，共感染缩短了幼虫的寿命，进而减少了V. culicis的孢子生成时长。总体而言，共感染对V. culicis产生了净负面效应：其最终产出的孢子量低于接种感染所用的孢子投入量。共感染还通过缩短宿主预成虫阶段的寿命，对致病力更强的寄生虫Edhazardia aedis的水平传播产生了负面影响，但相较于V. culicis，Edhazardia aedis的传播潜力所受负面影响更小。
(5) 本研究结果表明，共感染既可直接影响寄生虫的传播机会，也可通过调控宿主生活史间接产生此类负面效应。此外，本研究还发现，寄生虫传播效率取决于非生物环境的综合作用。