Algis Budrys' "Silent Brother" (as by Paul Janvier) (short story, symbiosis)

This one is a good read, from among the many stories that share its main trope: sentient alien parasites find an initially reluctant & then willing host in humans because of the ... sort of ... rent aliens are willing to pay.

Story summary.

Four men comprising the first human expedition to Alpha Centauri have returned after their 6 months (?) long trip - with an unusual gift. A gift government considers so dangerous it has them quarantined.

Meanwhile, Harvey Cable, the inventor of the stardrive & now a cripple living some 20 miles from the site of expedition's landing, is finding his uneventful life changed in unexplainable ways.

Of course, there is a link between the returned expedition & the curious events now happening in Harvey's life...

See also.

1. Larry Niven's "Smut Talk" (download) & Hal Clement's "Needle" are similar in that they too feature sentient alien parasites that use humans as hosts.
2. Howard L Myers' "Partner" (download) has a plot somewhat akin to curious events in Harvey's life. And the general style of this part has been a favorite of Henry Kuttner & C L Moore - their fantastic story "The Prisoner in the Skull" immediately comes to mind. May be Robert Louis Stevenson's "The Strange Case of Dr Jekyll and Mr Hyde" is the canonical story about this trope (but I haven't read Stevenson's version).

Collected in.

1. Isaac Asimov & Martin H Greenberg (Eds)' "Isaac Asimov Presents the Great SF Stories 18 (1956)".
   

Fact sheet.

First published: Astounding, February 1956.
Rating: A.
Listed among the stories from John Campbell's Astounding/Analog.
Related: Stories of Algis Budrys.