POKROV, Russia — The coarse medical treatment that Aleksei A. Navalny, a Russian opposition leader, is receiving in prison poses a lethal risk to his health, his personal doctor told journalists on Tuesday. The doctor was subsequently arrested, along with several reporters.
Mr. Navalny, the pre-eminent political opponent of President Vladimir V. Putin, is 44, and survived a poisoning with a military nerve agent last summer that Western governments called an assassination attempt by the Kremlin, which has denied any role.
In January, he voluntarily returned to Russia after receiving treatment in Germany. Upon arrival, he was arrested at the airport for a parole violation related to a suspended sentence from 2014.
In recent weeks, Mr. Navalny has experienced back pain and numbness in his legs, according to his social media accounts, which post under his name with information he conveys to lawyers. The lawyers said in a recent interview that they suspect these conditions are either lingering symptoms of the poisoning or are the result of a herniated spinal disk.
Mr. Navalny is also now nearly a week into a hunger strike over what his social media accounts describe as prison officials’ failure to provide him with sufficient medical care.
In addition, prison doctors said on Monday that Mr. Navalny showed signs of a respiratory ailment. According to state media, they had him moved into an infirmary on the grounds of the penal colony where he is serving a sentence of more than two years on the parole violation.
Mr. Navalny’s temperature rose to 100.5 degrees Fahrenheit, and he had what he described in a social media post as a severe cough.
One obvious possibility, the coronavirus — known to spread easily in prisons — has not been diagnosed. The authorities have tested Mr. Navalny for the virus, the Izvestia newspaper reported. Mr. Navalny said in a social media post that he suspected tuberculosis, a common contagion in Russian prisons.
Anastasia Vasilyeva, his personal doctor, told journalists on Tuesday that she was “greatly troubled about his health, about what can happen tomorrow with his health.”
“I understand very clearly from symptoms that he has now, that it can lead to a very severe condition, and even to death,” she said at a checkpoint on a muddy road outside the penitentiary in Pokrov, about 60 miles east of Moscow, after guards declined her request to examine Mr. Navalny. “This is an insane violation of human rights.”
The refusal to allow access was expected. Ms. Vasilyeva, who leads an organization of medical workers in the political opposition, the Doctors’ Alliance, showed up outside the prison with half a dozen or so fellow doctors to demonstrate the authorities’ refusal to grant access to specialist care.
Their white gowns flapping in an icy wind, the doctors milled about in the desolate spot.
The prison, Penal Colony No. 2 in the Vladimir Region, is surrounded by a frozen swamp. The doctors said they intended to hold a regular protest at the site, within view of the coiled barbed wire of the prison wall, until Mr. Navalny receives proper treatment. The prison authorities say they provide adequate care.
“We don’t plan to stand down,” Ms. Vasilyeva said. “We will come tomorrow, and the day after tomorrow, until they let us in and we can understand what is happening with Aleksei.”
But after their action Tuesday, the police detained Ms. Vasilyeva, several other doctors, and journalists including a correspondent for CNN, Matthew Chance. Mr. Chance was later released.
After the chemical weapon poisoning, Mr. Navalny was evacuated to Germany for treatment. The German government said it had discovered traces of Novichok, an exotic nerve agent that can be lethal to the touch and is known to have been manufactured only in Russia and previously in the Soviet Union.
The poison was also used in the 2018 attempted assassination of a double agent, Sergei Skripal, in Britain, according to the British government.
“There is nothing difficult to understand here,” Ivan Tumanov, the director of Mr. Navalny’s movement in the Vladimir Region, said in an interview on Tuesday of Mr. Navalny’s worsening health. “Putin wants Navalny dead, so he isn’t allowing doctors to visit.”
Supporters say the prison authorities have also resorted to petty harassment. Nearby Mr. Navalny, who is now well into a hunger strike, they have been grilling chicken, Kira Yarmysh, Mr. Navalny’s spokeswoman said on Tuesday.
Mr. Navalny’s team suggested that a main concern now is tuberculosis. While mostly a bygone threat in developed countries, and treatable in its usual form with antibiotics, the disease is a lingering killer in Russian prisons.
Rail-thin, exhausted men fill the tuberculosis wards. And harsh conditions have spawned new strains peculiar to Russian penal colonies, alarming global health experts for years now.
Seeking to spend time in the infirmary to avoid violence from other inmates, prisoners will sometimes try to get sick on purpose or extend the duration of their illness by refusing to take the full course of antibiotics or by swapping spittle.
The result, infectious disease experts say, is a proliferation of forms of tuberculosis resistant to antibiotics.
Mr. Navalny’s social media accounts said on Monday that three inmates in his barracks had been hospitalized for tuberculosis.