Cases of a waterborne disease caused by a microscopic parasite could continue for two more weeks, an expert has warned, with businesses predicting losses of “many thousands” of pounds.

Around 16,000 households and businesses in the Brixham area of Devon have been told not to use their tap water for drinking without boiling and cooling it first.

Paul Hunter, professor in medicine and infectious disease expert at the University of East Anglia (UEA), said residents should “expect to see further cases for at least 10 days to two weeks”.

The parasite could “absolutely” still be in the incubation period for lots of residents, he told BBC Breakfast on Friday.

Mr Hunter said: “One of the problems when you’re investigating outbreaks like this is that the incubation period can be about 10 days to two weeks.

“So often in the past when I’ve been involved in investigating outbreaks, by the time you know you’ve got a problem, the problem has resolved itself anyway, but you can’t guarantee that.

“Yeah, even if they have stopped all new infections by now, you would expect to see further cases for at least 10 days to two weeks.”

Michael Smith, co-owner of the Venus Cafe near Brixham, told BBC Radio 4’s Today programme they had seen a 40% drop in business in the last two days and had not been contacted by South West Water (SWW) “in any fashion”.

He said: “During the week at the minute we’re not super busy, but we’re losing four, five hundred pounds per day the last couple of days.

“Come the weekend, sunshine next week and the week after, we’re talking many thousands (of pounds).”

Mr Smith said the cafe only found out on Wednesday it was in the affected catchment area, and that plans by SWW to set up a telephone helpline for businesses would not be very effective.

He added: “This parasite is not rare, it does occur annually, so they should know how to deal with it.”

Aaron Richardson, a receptionist at Wall Park Touring Caravan campsite in the town, told BBC News customers had contacted the park stating it was “too risky” to visit.

He said the park was left without fresh water until Thursday night and had also not been contacted by SWW.

The UK Health Security Agency (UKHSA) said 22 cases of cryptosporidium, a waterborne disease caused by a microscopic parasite, had been confirmed in the fishing town.

SWW issued a “boil water notice” for Alston and the Hillhead area of Brixham after water tests showed “small traces” of the parasite, which causes sickness and diarrhoea.

SWW chief customer officer Laura Flowerdew said on Thursday a damaged air pipe in a field containing cattle was a potential source.

She told Sky News the company had identified a damaged air valve near the Hillhead reservoir, adding: “It’s in a farmer’s field and I understand that there are cattle in that field and therefore there’s a possibility that that is therefore the source of the contamination.”

Residents are being urged to boil water and let it cool before drinking it, preparing or cooking food or cleaning their teeth, though the company said water can continue to be used as normal for washing, bathing and flushing the toilet.

The disease can be picked up directly from the faeces of another person or animal, from swimming in or drinking contaminated water, or even by eating contaminated food such as unwashed vegetables.