It is funny to think that diseases can be used to cure other diseases. It is true, though. For centuries, scientists have found ways to use deadly, pathogenic bacteria, viruses and protozoa to cure deadly diseases caused by other pathogens.
It may seem uninteresting to heal one illness with another, but she has worked over and over again. And it's not always that scary. Other microorganisms, especially viruses and bacteria that are not necessarily harmful to humans, have also been used to treat deadly diseases.
Syphilis was incurable throughout much of history and often led to death within four years. The worst form is neurosyphilis, which is an infection of the nervous system by syphilis and is often the final stage of the disease. Neurosyphilis is accompanied by blindness, insanity, paralysis, and then death. Most syphilis patients were in asylum until their death.
The Austrian psychiatrist Julius Wagner-Jauregg began developing anti-syphilis therapy in the 1880s. He turned to pyrotherapy – the artificial induction of a fever, in this case through the introduction of a more manageable pathogen. The high fever caused by the introduced infection kills the incurable disease and the curable disease is treated afterwards.
Dr. Wagner-Jauregg tried unsuccessfully to use tuberculosis antigen and the typhoid and typhoid vaccines to cure syphilis. In June 1917, however, he got a break when a wounded soldier suffering from malaria was sent to the psychiatric ward of the hospital where he worked. This was clearly a mistake, as the soldier had no mental problems. However, the doctor took the opportunity to work on his pyrotherapy for syphilis.
Dr. Wagner-Jauregg drew blood from the soldier and injected it into nine people suffering from advanced syphilis. The malaria causing plasmodium protozoa caused a serious fever that killed the syphilis causing Treponema pallidum bacteria. Dr. Wagner-Jauregg cured the six survivors, who were now suffering from malaria, with quinine.
Dr. Wagner-Jauregg published his findings in 1918. He found that syphilis is killed when the body maintains a temperature of 41 degrees Celsius for six hours. His treatment soon became the method of choice for syphilis. However, it had its drawbacks, although it was considered successful.
Syphilis patients often suffered from complications when they were injected with another blood type. They also inherited the blood disorders of their donors. The deadly malaria strain used at this time could also cause anemia and kidney failure. The physicians later switched to the less deadly Plasmodium vivax strain. This treatment was abandoned after the advent of antibiotics. 
It is particularly surprising that one of the world's worst diseases can be used to treat other deadly conditions. Scientists have found a way to cure HIV for leukodystrophy and Wiskott-Aldrich syndrome, two deadly diseases that often affect children.
To be clear, we do not use HIV itself, but viral vectors, some of which come from HIV. As in gene therapy, a viral vector is used to transport genetic material into cells. In 2010, a team of Italian doctors under the direction of dr. Luigi Naldini 16 children HIV-based virus vectors. Six had Wiskott-Aldrich syndrome, while the other ten had leukodystrophy.
Three years later, they observed that six of the children were slowly recovering from the disease. Three suffered from Wiskott-Aldrich syndrome and the other three suffered from leukodystrophy.  The other ten also showed signs of recovery. The procedure is inconclusive as it is still in clinical trials.
CRISPR (pronounced "crisp") means "Clustered Regularly Interspaced Short Palindromic Repeats". It is used in CRISPR-Cas9 gene processing technology that allows scientists to process the DNA in cells.
As scientists focus on using CRISPR to modify unfavorable genes, researchers at the Rutgers Cancer Institute in New Jersey are trying to cure cancer. CRISPR is suitable for cancer treatment as cancer cells that travel through the body tend to return to the tumor from which they originate.
Using the CRISPR technology, Rutgers Cancer Institute researchers injected these cancer cells with the anticancer S-TRAIL protein. The S-TRAIL-containing cancer cells killed other cancer cells in the tumors as they invaded. Then they essentially destroyed themselves. However, the technology was not tested on humans, and the experiments were limited to mice. 
The cowpox virus was used to make the first vaccine against smallpox, a deadly virus that has infected millions of people, until it was eradicated in 1977. Vaccine is the reason why vaccines are called vaccines. The name was derived from vaccinus the Latin word for "cow".
While we speak of Engl. Edward Jenner owe the manufacturing of the first smallpox vaccine, we know that the ancient Chinese and the Middle East have deliberately infected themselves with smallpox to make themselves immune to the virus for centuries.
Dr. Jenner developed the smallpox vaccine after observing that milkmaids had never contracted smallpox. Later, he realized that they had been infected by cowpox, a closely related virus, by the cows that milked them. Dr. Jenner proved his theory in 1796 when he deliberately infected eight-year-old James Phipps with cowpox.
Dr. Jenner infected Phipps with smallpox for a month and a half after infecting him with cowpox. Phipps never developed smallpox, suggesting that he was immune to the virus. Dr. Jenner later published his findings. The smallpox vaccine, which later eradicated the disease, came from the vaccinia virus, another closely related virus. 
Poliovirus causes polio, which used to be one of the deadliest diseases. Fortunately, today it is on the brink of extinction. In 2017, only 22 cases of polio were reported, far from the 350,000 reported in 1988. Interestingly, scientists are developing a method to cure the once-deadly glioblastoma (GBM) disease, a rare and deadly extremely aggressive form of brain tumor. Glioblastoma is treated with surgery, radiation and chemotherapy. However, it often returns and kills the patient within a year.
Poliovirus therapy was developed by researchers from the Duke Cancer Institute, Durham, North Carolina. They have genetically engineered the poliovirus to create a new virus called PVSRIPO, which is injected directly into the brain tumors caused by glioblastoma.
A clinical study with 61 glioblastoma patients showed a survival rate of 21 percent. This seems small until we realize that patients who receive standard care have a survival rate of only four percent.
Although PVSRIPO looks promising, it can cause some adverse side effects, depending on the location of the tumor in the brain. 
5 Bacteriophage Therapy
In 2015, 69-year-old Tom Patterson was diagnosed with pancreatitis when he visited Egypt with his wife. The conventional treatment did not work and he was later flown to Frankfurt (Germany). The doctors drained the fluid around his pancreas to find that he was infected with drug-resistant bacteria Acinetobacter baumannii .
Patterson was later flown to Thornton Hospital, San Diego, California, where a drain was introduced around his pancreas to control draining. Unfortunately, the drain slipped and the fluid seeped into his abdomen and bloodstream. Patterson soon got a high fever, severe pain and shortness of breath. He also fell into a coma that lasted about two months.
Doctors opted for bacteriophage therapy as a last-ditch attempt to save his life. In contrast to what the name suggests, bacteriophages are viruses and not bacteria. The name means "bacterial eater" and refers to a specific class of viruses that attack bacteria. Each bacterium has a bacteriophage that has evolved to replicate.
Bacteriophage therapy refers to the use of these bacteria, which attack viruses to cure bacterial infections. It was the best way to deal with deadly bacteria until antibiotics came. The results are not scientifically proven.
Nevertheless, the therapy worked and Patterson slowly recovered from the coma – until 19459011 A. baumannii bacteria mutated and developed a resistance to the virus. Doctors solved this problem by introducing a newer virus strain into Patterson's body until he was finally cured. 
4 Maraba virus
Scientists have always known that the Maraba virus (also known as the MG1 virus) attacks cancer and destroys cells. However, scientists from the Ottawa Hospital and the University of Ottawa have discovered that the Maraba virus also attacks and destroys HIV-infected cells.
HIV works through the infection and rapid multiplication of cells in the immune system of its hosts. However, some HIV-infected cells stop becoming available after some time while others reproduce.
Physicians often administer antiretroviral drugs to suppress HIV. However, the drugs only work on active HIV-infected cells and have no effect on the resting cells. The dormant cells are activated and begin to proliferate rapidly when the patient stops taking antiretroviral drugs.
Laboratory tests have shown that the Maraba virus destroys dormant HIV-infected cells, suggesting a possible cure for HIV. However, the method is not conclusive since tests were only performed in the laboratory and this method was not tested on animals or humans. 
3 Coley toxin treatment
Coley toxin treatment uses bacteria to treat cancer. The procedure is named after William Coley, a New York bone surgeon who developed it in the 1890s. Coley invented the treatment after observing that patients who become infected with bacterial disease during a recovery from cancer surgery often outperform non-infected patients.
Coley believed this had happened because the bacterial infection strengthened the patient's immune system. So he started injecting live bacteria into his cancer patients. Later, he switched to dead bacteria because living bacteria could still cause deadly infections.
Scientists disagree on how the process works. Some believe that the injected bacteria strengthen the immune system against cancer cells. Others believe that the bacteria actually promote the production of a protein called interleukin 12 (IL12) or tumor necrosis factor (TNF) proteins that fight cancer cells. Another group believes that the high fever kills the cancer cells, just like the pyrotherapy procedure we mentioned earlier.
Nevertheless, Coley's toxin treatment had mixed results. It worked in some patients but not in others. However, it was spread until the early 1950s, when it was replaced by other cancer treatments such as chemotherapy. Even today, an improved version is used in which genetically modified bacteria are used. 
2 Predatory bacteria
Predatory bacteria are those that attack and eat other microorganisms. Predatory bacteria work by attacking and breaking through the walls of the hostile bacterial cells. Inside, it eats the guts of the bacterium before it multiplies and attacks other, similar bacterial cells.
Scientists are already working on using predatory bacteria to treat other bacterial infections, especially superbugs that are immune to normal antibiotics.
In November 2016, the BBC reported that scientists from Imperial College London and the University of Nottingham had successfully killed Bdellovibrio bacteriovorus predatory bacteria by Shigella a deadly genus of bacteria, This causes food poisoning and kills more than one million people each year.
Scientists observed Shigella that populations decrease 4000-fold after exposure to B. Bacteriovorus in the laboratory. Another test in fish larvae showed that the survival rate of larvae infected with Shigella increased from 25 percent to 60 percent. Scientists are planning tests B. Bacteriovorus on other deadly human bacteria, including Salmonella and E. Coli . 
1 CAR-T Therapy
T cells play an important role in the body's immune system. Recently, scientists have developed a method of using the T cells to produce a chimeric antigen receptor T cell therapy (CAR-T therapy), an anticancer treatment.
CAR-T therapy extracts natural T cells in the body and programs them with chimeric antigen receptors that greatly enhance their ability to detect, bind, and destroy cancer cells. The genetically modified T cells are tailored to the specific cancers of the patient, making them perfect cancer cell assassins.
However, CAR-T therapy is used only as a last resort because it can cause a variety of side effects including brain inflammation. The procedure is also time consuming because the T cells must be tailored to the patient. The whole process could take four months.