Are you farming human?

May work for some communicable diseases. Won't work for all communicable diseases, though; for example, siphilis, hepatitis, herpes, tuberculosis, leper etc. don't just go away after one year. In general, quarantine is useful for slowing down the spread of a communicable disease, not for curing it. If diseases just went away on their own within a year, doctors would starve.

I think yuou mean infectious diseases, rather than illnesses. Couple of other points needing clarification. 1. They live about 6 decades longer than Earth humans, that sounds like they spend most of their lives being elderly. 2. What is "a year"? This matters because infectious disease cycles tend to follow the seasons. If Hope's year is shorter than a Terran year, then your isolation period may be shorter. If Hope's year is far longer, say 250 Terran years, then ... play with that.

@Rich: "...they spend most of their lives being elderly", that rather depends on your definition of "elderly", doesn't it? Much of what we associate with being elderly is really the result of inactivity &c. Consider the concept of "health span", or the example of a couple of my neighbors. One retired in his 60s, sits in front of the TV drinking beer & smoking, and has multiple serious health problems. The other pursued a physically and mentally challenging career well into his 90s, and lived to over 100.

Significant numbers of diseases exist is reservoirs of other species (bats, birds, pigs, etc). Occasionally a germ will make the jump from animal to human, and some of those can shift to being able to jump from human to human. The mass culling of domestic birds in Asia in the early 2000's were a desperate attempt (apparently successful) to not give the dangerous avian-to-human virus a chance mutate to a human-to-human virus. It was not a complete success, as the virus had already jumped to wild avian populations.

@MichaelRichardson's point is rather important. Are you 100% confident the native flora/fauna can't act as a reservoir for any human diseases? Are you 100% sure the pets themselves can't act as a reservoir? Reservoir species may be infected all the time with a disease humans get over with time (the reservoir species' immune systems don't attack it, but that's fine, because it doesn't make them sick). You imported Earth species, and even if they're not pets, even in quarantine, people will likely be exposed to random small mammals, bugs, etc.

@jamesqf "Much of what we associate with being elderly is really the result of inactivity &c." Okay that sounds a bit woo. Two extreme examples don't change the general condition of physical aging: its effects can be minimized and a positive outlook can be maintained, sure, but neither can alter the plain facts that wounds and fractures take longer to heal; eyesight and hearing diminish; teeth crack; reaction times lengthen; pulminory function is lessened; and so on. It's inevitable, unless you have some worldbuilding reason why not.

@AlexP Surely that is covered by points 6 and 7 (tests for 99.9% of known diseases with 98% accuracy followed by cure or exile etc.)?

@MichaelRichardson - not just active flora and fauna, but also what we're seeing here with the thawing permafrost on the tundra: diseases whose hosts went extinct may be reintroduced by other means. You've also got the problem that "successful" diseases are the ones which don't cause too much damage; but when they jump species they can be disastrous, i.e. unsuccessful. COVID-19 could well have been one of those: bats can survive with the virus - thrive, even - because they maintain a higher body temperature and sleep inverted. Humans, not so much.

@rich The SciShow youtube channel had an excellent episode about bats, their immune system and how the physical effects of the exertion of flying makes them an ideal breeding ground for diseases without being wiped out by them.

@Rich: You've totally missed my point. If people regularly live to 130 or whatever, they will spend most of that time being "middle aged". All those things you list don't show up until the last decade or two of the average lifespan, whether that span is 70 or 130.

@jamesqf Well, there's nothing to indicate Hopeans are especially bred for longevity. I'm just going by the available information, which is that real world Earthlings who live to 110, 120, spend most of their lives being elderly. You are wrong as a matter of fact when you say the condition of being elderly shows up in the last decade or two of life.

Yes, if you also kill anyone that has any disease, during your quarantine. This will eliminate carriers, and remove breeding spots for the diseases. The duration of the quarantine needs to be equal or longer than the longest spore-survival-time of any pathogens, so something in excess of 10 000 years...........So actually, NO

Randall Munroe discusses this in his book "What If".

@MBak And as I recall the answer is "It'd be highly unpleasant and it still wouldn't work."

@AlexP No, doctors would not starve, quality of healthcare would increase.

@jamesqf There where times when average live span was 40 years, I do not think efekts of age are relative to the live span. I think they are genuine physical degradation. Try to run some complex technical device for 100 years. It will be visibly aged. Of course a human body is good in replacing degraded parts, it happens a lot on cell level. I can not tell why, but I am not surprised that self-replacement of a living human works impressively well, but is not perfect.

HIV/AIDS: Incubation period 12 years. Good luck.

@Volker Siegel: Most of that AVERAGE 40 year life span was due to infant & childhood mortality. If a person managed to survive to early adulthood, and managed to escape the effects of wars & plagues, they had a good chance of living to an age we consider to be old.

You sure wouldn't get rid of mental illness. In fact, it's the perfect way to increase mental illness.