Friends and backers of Ward 5 Alderman Sean T. O’Donovan’s are struggling to hold together his bid for the 2nd Middlesex District state senate seat left vacant by the death of Charles E. Shannon Jr.

Despite the backing of Mayor Joseph A. Curtatone and DPW Commissioner Stanley Koty, O’Donovan’s campaign received a body blow when the mayor’s sister started telling others she had entered the fray.

Tuesday night, Maria C. Curtatone held a private party at her Prospect Hill home for backers  where she was expected to confirm to them what she had been telling individuals close to her for the last week.  Instead, it was a quiet dinner with no talk of politics. Hmmm.

The O’Donovan camp is said to have done a poll showing that only 5,000 votes will be coming out of Somerville, making it even more difficult to overcome candidates from outside the city if other Somerville politicians are in the race.

The most bizarre twist is that O’Donovan, who begged the mayor and Koty for the green light to oppose in the Sept. 14 Democratic Primary State Rep. Patricia D. Jehlen, D-Somerville, and was denied, must hope that Jehlen wins Shannon’s senate seat, so he can run for her then open state rep. seat.

So far, the only other "announced" Somerville candidate for state senate seat is Jehlen, who with Shannon secured funding to repair the Lowell Street Bridge in the last weeks of his life.

The other Somerville candidates in the mix are: Shannon’s Chief of Staff Sean J. Fitzgerald, former state representative Joseph Mackey and Alderman-at-large William A. White Jr.

White would run in the Republican Primary. All others are running for the Democratic nomination.

The primary is scheduled for Aug. 30 with a final election Sept. 27.