I don't know how much strength he has left, because he is too weak to stand and cannot even stay conscious for more than a minute. When he passes stool, he cries. I gave him around 0.5 ml of the febendazole.
The ticks are much less now, after all the hand-picking. There are small ones remaining.
But I don't think I have time on my side. I just pray that he somehow makes through this by some miracle.

My heart goes out to you. What a sad way to spend Christmas. Good luck to you and the pup.

Getting him to a vet is your best hope. If he's that weak, it may be that he simply needs energy before solid food, and some sort of medicated glucose / electrolyte solution would help . . . or maybe he's suffering something else . . . birth defect? infectious disease?

If you can't get him to a vet, are there any experienced breeders in your area. Breeders learn a lot about reviving puppies, and many of them are generous with helping rescues.

Is he dehydrated? (Use the pinch test. Gently pinch up the skin over his spine, near his shoulders. If he's properly hydrated the pinched up skin will rapidly go back to lying flat. If he's dehydrated, it will stay pinched longer and go back to the original position slowly). If he is dehydrated, you may be able to hydrate him using a syringe without a needle to gently push fluids down his gullet. An electrolyte solution with some sugars (eg., glucose) is probably better than plain water. If you have access to veterinary electrolyte, that's best. But in a pinch, something meant for dehydrated people or babies would probably be better than plain water.

Thanks sandgrubber...though yesterday was a tough day, things began to improve in the middle of the night, and he drank some milk and felt better and more alert. Today he is noticeably stronger, since he is more conscious, sleeping less, and trying to walk. I have a hunch the deworming has done the job.
I have given Mebendazole...does anyone know when I need to repeat the dosage? I searched for sites with mebendazole dosage for puppies, but couldn't find any.

I have also thoroughly applied the flea powder on him. Hopefully, he will get better.
Thanks for all help.

Well done sreebh, you are doing a great job.
What about the ticks have you managed to get them off the pup?

It is common to deworm puppies every two weeks. I think this is recommended due to the eggs not being killed by the first dose . . . and pups are easily re-infected.

He said earlier that he managed to get most of the ticks off manually. I think the puppy is so weak because he is full of fleas, ticks, and worms. I hope he will recover with some tlc and a tad more parasite removal.

To the op, you are doing a grand job trying to help care for him. Do you plan to keep him if you can nurse him to health? That would likely surely make his holidays pop, and yours too!

Thanks for all replies. I will be returning his sibling to the dog shelter, but I'm keeping this one for a while, till he is strong enough. His sibling is almost twice his size and has started to tear down the house! They are very much bonded, but I have no choice but to give back as I live in an apartment, and the neighbors are not so dog-friendly. Also I have pigeons, and ever since the dogs came, their movements have got restricted.

You are a good soul sreebh xxx

You are indeed a good soul Sreebh. It's a hard job you've taken on. Everyone above is quite right: parasites are unbelievably bad for young puppies, especially if, as with your little one, they're being attacked on multiple fronts, with fleas, ticks, AND worms. You can see the fleas and ticks, but you can't see the worms, and they could be doing serious damage. With a puppy so weak, I'd ask a vet about worm treatment. It might be harsh, but it could save him. Worm treatments these days are very effective, and safe to use even on young puppies-- I know; my own first pup came riddled with worms as big as you'd dig up out of the garden, at six weeks. One treatment and a few goopy poops and he was done with them. Keep up with regular treatments, and you'll never see the problem again.

As far as natural treatments go, if you have a seriously infested puppy, you might just have to bite your tongue and go for the more serious stuff. An adult dog will be sickened by a severe infestation, but they can shrug it off eventually with care. A puppy can't. You need to get rid of those parasites completely and as soon as you can. Frontline is your friend; it's a spot-on treatment you just put on the back of the puppy's neck. It is absorbed through the fat layer, and any flea that bites is killed, as are any eggs it might lay. It's available in a spray as well, to de-flea your dog beds (do you have cats? Dog frontline should NEVER be used for cats-- it hurts them). Drontal will kill the worms, but ask your vet for their recommendation. All in all it won't be that expensive and it will take them out. I've been using Frontline for 15 years. It's good stuff.

On the natural front, grapefruit is even stronger than lemons for repelling bugs. Rub the skins around dog beds (and your bed: fleas eat you too) and put the empty skins on the radiator so their scent permeates your house. It doesn't hurt that it's a nice scent.

Don't worry about getting out the big guns here.

Thank you very much. I eventually took him to a vet, because though he was gong uphill it wasn't at a pace I wished him to. The vet examined his stool and said the mebendazole hasn't done its job, the eggs of worms are present in the stool sample. So he has been given a three day course of fenbendazole.
I am also using a spray for the fleas (fipronil)...a one-time application is expected to stay on for over a month.
He is now much better, but not walking well yet. I bathed him and his big brother today, and he looks just gorgeous.

Btw, we haven't given his brother back to the shelter yet, the main reason being...we cannot bring ourselves to do it. The brother is too naughty for words, yesterday he bit my cheek and my daughter's ear...he is absolutely unstoppable when he goes into that biting frenzy. I am also not sleeping well ever since the dogs came, because of the biting and playing in the middle of the night. He will not allow us to lock our room while we sleep, and now he wants to sleep right by our side. He is like a small human baby, and it feels good to hug him and sleep, but the biting is horrible. I tried crying when he bites, I tried behaving like another dog and barking back at him, but he doesn't get the message. I slap him lightly on his forehead at times, but feel very guilty afterwards. I am re-living the times when I was the mother of a new-born, waking up several times in the night. I know biting is something they do naturally as children, I just feel overwhelmed having a sick pup and his hyperactive brother!!!