How to get rid of fleas in house without animals nor carpets

tl; dr

I started having problems with fleas last week. I don't have and never had pets and no one in my close circle has reported problems, so I am puzzled about the problem. Therefore, this post is comprehensive with all the data I have at the cost of being long.

Unlike this thread, I am fortunate to have had only a few fleas so far, but also unlike the thread, they are biting me and not the animal. I have been bitten about 15 times in the course of a week.

I would like to understand the problem, solve it effectively, and prevent a recurrence.

Some photos

I believe they are fleas because I have bites that look like flea bites, I saw one creature jump when I tried to grab it, and I put one that I had caught and squeezed sideways under a microscope (I put scotch tape on top of it when it was on my skin, then squeezed it between my nails below the scotch tape, which squeezed its sides).

Parts of the body of the sideways flea other than the ones I posted below look just like the photo of a flea in the side bar of the Britannica article on fleas, especially the long hind legs. Unfortunately, 100x is the minimum on my microscope, so I cannot post a full picture of the sideways flea. I can take and post more photos from the microscope as needed.

Here are some photos with a phone camera or through a 100x microscope.

Bites after three days:

First flea I caught:

First flea under the microscope (top view of flat body):

Third flea I caught (that got squeezed sideways):

Mouthparts of sideways flea in microscope:

Hind legs of sideways flea in microscope:

Chronology of events

Here is the full story. I never had a pet animal, cat or dog. On 27th August I started renting a room in a property by the seaside in Portugal, along with one other housemate who had lived there for years. The house has no carpets and 8 small rugs in the rooms.

On 2nd August I received a delivery with my belongings from the UK. They included clothes, bedding linen, and a memory foam mattress. They were transported by a removal company that gathers consignments from multiple senders and send them all in a truck. On 13th August I left for two weeks of holiday in the UK and returned on 30th August. On the 18th I spent several hours cleaning a dusty and humid garage (the air here has 81% humidity and the garage is almost always closed). Also on the 18th, two cleaning people came to clean the house, as they do every month.

On either 19th or 20th September, I noticed the first bites. I took several days to recognize them as I never had flea bites as an adult. At first I wondered if I had been bitten by one of the spiders I saw in the garage.

On Saturday 21st I woke up and was sure it was a flea because I was clearly bitten in three new spots on my left foot. I set the bed sheets aside and put on new sheets. I laid a trap of overripe fruit and vinegar as suggested here, which had no fleas after a day.

On Sunday 22nd I woke up with even more bites. I washed both sets of sheets and everything else on the bed, including the cover for the mattress, but not the mattress, the pillow, and the comforter, which I left on sunlight for the whole day. The bed frame and wooden board were the only things I hadn't touched, so I vacuumed them. Near where the wooden board joined the bed frame, I saw a small animal moving (if it were a flea, it was a fat one) and I instinctively directed the vacuum at it. I did not see it anymore, so it may have gone into the vacuum bag. I wanted to see if it had blood, so I opened the bag outside and could not find the animal among the debris. Let me call this flea #0.

A host who stayed over on Saturday 21st for the night in another room noticed a bite later on Sunday.

After vacuuming flea #0, I thought I had solved the problem, slept in the bed with the clean sheets, and was not bitten on Sunday night.

On Monday 23rd in the evening, in the same bed, I felt a tickle in my leg: it was two small fleas. I tried to grab one and it jumped immediately. I killed the second one by squeezing it in between my nails. I'll call this one flea #1. I looked for the other on the floor, tried to grab it, and it jumped again. Neither had bitten me. I took a sleeping bag and left everything else in that room. I took a shower to get rid of any other fleas, and went to the fourth room in the house, which was empty (the other three rooms are my room, the other housemate's room, and the room where the guest stayed). I slept in the sleeping bag. I woke up several times to check on any tickle. I felt surprised and worried to find another flea at 4 am because I thought I had been very careful. I killed the flea the same way as flea #1. I'll call it flea #2.

On Tuesday 24th (yesterday), I tried an idea to both kill other fleas and get data on the situation in my room: I would offer myself as bait by going into bed for an hour without clothes, and check any tickling and the linen every minute for fleas. I thought that maybe my presence caused the eggs to hatch and I would know if eggs had been laid. I did this yesterday and after 15 minutes I saw a flea on the bed. I tried to catch it twice and it escaped. I had an idea to get scotch tape to immobilize it, so I inspected my body, left the room, and came back with tape. Three minutes later, I found it on my left leg, put a piece of tape on it, and squeezed it between my nails. I'll call this flea #3. I stayed in the room for another 45 minutes and did not notice any other fleas. I inspected my body, left the room, took a hot shower, and went to sleep in the living room, as one was occupied by my housemate and the three others had had fleas in the last week. I recorded a video of my legs and the lower end of the bed, watched it backwards around the time when I found the flea to see where it was coming from, but resolution is too poor for the flea. In the shower, I felt an itching while in the shower on the outer part of my right lower leg, where it was difficult to see, and today it turned out to be four more bites. This invalidates my method because a blood meal causes fleas to be able to reproduce.

My housemate has not been bitten so far.

Possible vectors

I considered several vectors for the fleas, all of them unlikely:

• I got them from my holiday in the UK. I had brought the sleeping bag where I found flea #2 there, but had not used it. But none of my five friends who stayed at the same house for two weeks have reported any problems.

• I got them on when I cleaned the garage on the 18th for 6 hours. That garage is seldom visited, but none of the other people who have visited it in the last few years (including me) have had this problem.

• The fleas migrated from the three stray dogs into the house. But the house has walls and gates that are always closed and I never saw a dog in the property. It also has a clearance of 2-3 m to the roads where the dogs walk. I asked the next door neighbor, who does not have fleas. The dogs have been here for at least a year and my housemate has not had this problem before.

• I got them from the two cleaning people, one of whom has a dog (that stays outside and not indoors). But they have been coming here every month for years.

• I got them from the three stray dogs when I went past them on the 17th in the morning. In early September I went running many times a week and the dogs often barked furiously and ran after me. This would explain why I got them and not my housemate, who only goes past the dogs in his car.

• One or more owners in the other consignments had a pet, their belongings had fleas, and the fleas laid eggs in my belongings. This does not explain why they did not hatch on 2-13 August and 30 August-18 September, when I had slept on them, but maybe they take this long to hatch.

If the stray dogs are the culprit, then I want to contact authorities to put them in a kennel. If it's the the truck-share, I want to start an insurance claim.

The current situation

I read the Britannica and Wikipedia articles on fleas and their lifecycle but I don't have enough knowledge or experience to determine the likely situation given this data. For example, I don't know if any fleas that may have bitten me yesterday are likely to reproduce in a few days, or if I would cause more eggs to hatch by lying on the bed.

I am keeping away from that room for now to avoid feeding the fleas and to ascertain whether fleas have spread to other parts of the house. If I have to visit the room, I may try the light-water-soap or sitcky paper traps in the thread I mentioned.

Questions and way forward

Finally, here are my questions:

• The Britannica article mentions that "The adult fleas pass freshly imbibed blood rapidly through their gut to produce fecal matter for the nourishment of their offspring." Could flea #3 have bitten me four times in 30 min yesterday and show no blood when I killed it right after? If not, then other fleas, inside or outside the room, are responsible for the bites I found this morning.

• I could try the same method again of visiting the room but taping the parts of my legs that I can't see (where I was bitten yesterday during my method to kill fleas and gather data) so that I don't get bitten again. I could also wear a wetsuit (which I have here) to avoid exposing skin or apply repellent on the skin. Would that be wise?

• The thread I mentioned suggests professional extermination in the case of hundreds of fleas. It would take 5 hours and $500 and is a good option as last resort. Would any other pest control methods work here?

• Any other course of action, or anything that I am missing in this situation?

Thanks for the long reading, and I really appreciate any help!