Are superspreaders also superreceivers?

For simplicity, we often assume that all hosts have an equal probability of becoming infected by and transmitting parasites and pathogens. But of course, we know that it isn’t how real systems work. For instance, in real systems, hosts vary in their propensity to become infected by pathogens, and that variation is one probable cause of the parasite ecology “law” that macroparasites are aggregately distributed among hosts. We call hosts that are highly susceptible to a given pathogen “superreceivers,” and hosts that are highly likely to transmit a pathogen are “superspreaders.”

Here’s a question for you to ponder: are superspreaders usually superreceivers and/or are superreceivers usually superspreaders? For instance, sex workers are at high risk for contracting HIV (=superreceivers) because they frequently change sex partners, and they’re also highly likely to spread HIV (=superspreader), if they have it, in comparison to the average person. In that case, the superreceivers are also superspreaders. When that happens, we might predict really explosive epidemics whenever “patient zero” is a superreceiver+superspreader, because R0 will be very, very high.

But consider the Tasmanian devil example that I posted about recently. Tasmanian devils that bite lots of individuals are highly likely to contract Tasmanian devil facial tumor disease; they’re superreceivers. But being bitten by an infected individual doesn’t seem to transmit the infectious cancer to the receiving host, so devils that bite frequently don’t transmit any more frequently than devils that don’t bite frequently. Therefore, the superreceivers in that system aren’t superspreaders.

Now let’s talk about a really cool system that I somehow haven’t blogged about yet. House finches are hosts for an emerging bacterial pathogen (Mycoplasma gallisepticum – Mg) that jumped from poultry into house finches in the 1990s. This pathogen causes conjunctivitis in the house finches – a symptom you don’t often think about in wildlife! In a really neat recent paper, Adelman et al. (2015) showed that birds that spent more time on bird feeders were more likely to become infected by (superreceivers) and transmit (superspreaders) Mg. This is a really cool example of a pathogen that appears to be transmitted by “fomites”: inanimate objects that the pathogen can survive on when off the host.

We probably don’t have enough examples in the literature to determine whether superspreaders are usually superreceivers or to look for generalities in systems where this occurs. But we’re accumulating more examples all the time! Stay tuned.

…if academics were at higher risk of developing conjunctivitis when they sought out free food, I’d have some very squinty-eyed colleagues.

Finch

Reference:

Adelman, J.S., S.C. Moyers, D.R. Farine, and D.M. Hawley. 2015. Feeder use predicts both acquisition and transmission of a contagious pathogen in a North American songbird. Proc Biol Sci. 282(1815): 20151429.

9 thoughts on “Are superspreaders also superreceivers?

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  3. My system (Phytophthora ramorum and sudden oak death) I think is an example of superspreader = superreceiver. In mixed oak woodlands P. ramorum depends on the California bay laurel tree for reproduction (infecting and replicating on the foliage). It is environmentally transmitted to neighboring oak trees (spillover), which are effectively dead end hosts, but also between neighboring bay laurel trees (or more specifically, bay laurel leaves). So, California bay laurel would be the superspreader and superreceiver

    • Hmmm, that’s interesting. So in this case, you’re calling a whole species a “superspreader” and “superreceiver” species? I usually think of that more as highly competent vs. dead-end/low competency hosts.

      • I think it could be conceptualized as a superspreader species, though traditionally these characterizations are for individuals. Paull et al. (2012) conceptualized this idea in “From superspreaders to disease hotspots: linking transmission across hosts and space” with the overall message being about factors influencing transmission heterogeneity in individuals, species, and the environment. The since spillover is a major characteristic of this system, the bay laurel is an “amplification species” building up and sustaining the pathogen. To be traditional, there could be superspreading individual trees, though to be accurate this would probably need to have a genetic basis in an otherwise environmentally controlled system. I recently read a section in Keeling & Rohani “Modeling Infectious Diseases in Humans and Animals” that introduced me to the “super-shedders.” Similar to a superspread, a super-shedder produces a lot more secondary cases, but it isn’t more likely to come into contact with the infection. Since plants are generally immobile for their lifetime their contact rate would be constant, so I think this might be a better characterization for individual plants that might otherwise be called superspreaders.

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