Arenavirus describes a group or genus of viruses, each distinct in their geographic region of origin as well as their severity. While not all are typically fatal, most Arenaviruses are severe and display symptoms such as high fever and acute haemorrhagic illness. 

Each arenavirus species is often associated with its own species of rodents which in turn is associated with a specific geographical region. For example, the high mortality species "Lassa fever" is associated with the Natal multimammate mouse in West Africa. 

Arenaviruses are transmitted by the consumption of contaminated foods and drinks as well as the inhalation of particulate rodents excretions. This disease can be further transmitted from person to person via direct contact with bodily fluids. 

There is no known treatment or vaccine for arenaviruses. 

Most commonly associated with the term trench fever, bartonellosis is a bacterial disease that, while carried by rodents, is most often transmitted to humans via indirect vectors such as fleas, ticks and body lice.

The symptoms of this disease are varied, but common signs of infection are inflammation of the heart and eye disease. 

Fortunately, bartonellosis is known to be treatable with antibiotics. 

Rodents such as rats and mice are the primary hosts of a species of roundworm called Capillaria hepatica. These roundworm species release their eggs into the environment via the death and decomposition of their host, whereupon they wait for the contaminated substance to be consumed. Once consumed, the roundworm infects the host by hatching in the intestinal tract and burrowing through the wall into the liver and bloodstream. 

They mature and feed upon the liver causing several symptoms such as inflammation and eventually liver failure. 

Due to the rarity of the disease, there are no known vaccines or cures. However, treatment exists to help with the inflammation, such as the use of steroids.

While the primary hosts of the species of tapeworm known as Echinococcus are carnivores, several species can use rodents such as rats and mice as intermediate hosts that pass the larval cysts onto domestic animals such as dogs and cats. From the infected animals, the cysts can contaminate food or water via faecal matter and infect a human. 

Much like the previous entry, this disease starts in the intestines, where the larvae hatch and spread throughout the body into vital organs such as the liver. Unlike capillariasis, though, this disease may not develop noticeable symptoms for years before the infected tissue grows. 

When symptoms do show, it is in the form of abdominal pain and bloody mucus. In severe cases, the tumour-like tissue can rupture, which can cause many more severe effects such as anaphylactic shock as the vast quantities of larvae are released into the bloodstream. 

One of the most common diseases carried by rodents is the Hantavirus. There are many different species of the Hantavirus, each with its own severity, flu-like symptoms, species of rodents and geographical location. The most dangerous of these being the Sine Nombre variant found in North America, Canada and Mexico. This variant can cause Hantavirus pulmonary syndrome, which is highly lethal.

The disease is transmitted via direct contact with infected rodent excretions and contamination or airborne particles. 

Leptospirosis is a bacterial disease carried by rodents, cattle and some domestic animals such as dogs. This disease is transmitted via human contact with the urine of an infected rodent or infected animals and from the soil, contaminated food, or water contaminated with the urine. 

Not only can leptospirosis bacteria survive in soil and water for months, but it can infect through the skin and mucus membranes too. This means that individuals working in regular direct contact with animals and freshwater sources are particularly at risk of catching this disease.

Symptoms of leptospirosis caused by rodents are similar to bad flu. While these symptoms can become severe in some cases, it is only potentially fatal if left untreated. Luckily this disease can be treated with antibiotics.

This bacterial disease is directly transmitted by infected rodents via a bite of an infected rodent or a scratch, thus the name. Humans can become infected if they consume food or water contaminated by rodents excretions or by handling them normally and being bitten by an infected rat.

There are two different bacteria that can cause this disease, and depending on which one you get infected by, you can experience different symptoms. 

Streptobacillus moniliformis infection will set in within three to ten days before symptoms are shown. These symptoms include flu-like symptoms such as vomiting, fever, muscle pain, headache, and rash. 

Spirillum minus will show symptoms seven to twelve days after infection. These symptoms include fever, ulcers at the wound site, swelling, swollen lymph nodes and rash.

Rat-Bite fever can cause severe complications on top of the displayed symptoms such as pneumonia and meningitis in extreme cases. 

Antibiotics can treat Rat-Bite.  

Rat tapeworms consist of two species of tapeworm. Hymenolepis nana and H. diminuta, of the two species, the former is the most common. 

The infection vector for these parasites is via consuming food or water contaminated by beetle or rat faeces. 

Rat tapeworm infections can be mild enough to go unnoticed, but in severe cases, there are several symptoms such as Abdominal pain, enteritis, diarrhoea, loss of appetite, restlessness, irritability, restless sleep and anal and nasal itching. 

All such symptoms are more annoying and discomforting to a healthy adult, but the effects can be more pronounced and severe if a child is infected. 

The salmonella bacteria is most commonly associated with raw chicken, but rodents are also carriers for it. The transmission vector for salmonella is the consumption of rodent faeces contaminated food and water. 

The symptoms of salmonella include diarrhoea, fever, vomiting and abdominal cramps, and typically, these show up in a mere 12 to 72 hours once infected.

Salmonella is also highly contagious and can be transmitted from person to person via hand contact, both direct and indirect. 

Another particularly virulent strain of salmonella is known as typhoid, which produces a much more serious set of symptoms.

While salmonella should go away by itself after a few days, typhoid is treatable with antibiotics, and there is a vaccine for it. 

The plague is one of the most well known and fear-inducing diseases associated with rodents. While most of the threat of the plague was eliminated by the discovery of antibiotics, it still exists in the wild as rodents serve as a reservoir of carriers. This means that it's possible to get the plague still today, and in fact, people in less developed countries are still at significant risk to it. 

The plague is transmitted to humans both directly by rodent droppings and other such contamination as well as indirectly via fleas and mites that infect the infected rodents.

The plague is split into three different types: the Bubonic plague, septicemic plague, and pneumonic plague. Each of them occurs depending on exactly how the plague was transmitted.

All three types of plague are lethal if untreated, but the septicemic and pneumonic plagues are even more so. The latter, in particular, has a 100% mortality rate if left untreated.

Thankfully all such plagues are treatable with antibiotics, and doctors can identify the symptoms quickly, especially if they know of any flea or tick bites on an infected persons body.

Toxoplasmosis is a protozoan infection caused by Toxoplasma gondii. It is most commonly transmitted to humans by domestic cats. This is because rodents act as intermediate hosts for the infection, and so when cats kill and eat them, they get infected. Then they contaminate human food and water via faecal matter. It is also possible to be infected by eating raw fruits and vegetables.

The problem with Toxoplasmosis is that it is hard to detect due to it not showing any symptoms for most people. In those, it does cause symptoms, for they can be severe with symptoms like organ damage, swollen lymph nodes, and brain damage.

Toxoplasmosis in pregnant women can cause miscarriage and stillbirths even if no other symptoms are present.

Trichinellosis is another nematode worm parasite commonly carried by rodents. The roundworm disease is transmitted to humans upon the consumption of undercooked meat. This happens because in the wild, the animal the meat came from likely ate a rodent that was a carrier, and as such, when its meat is undercooked, the parasite can survive and infect a human.

Trichinellosis larvae emerge from their cysts in the human stomach, and from there, they infect human tissue to mature. Typically they enter muscles and form new cysts, and their reproduction cycle begins anew.

Tularemia is one of the most infectious diseases known to scientists and is deeply interlinked with the population of rodents as they are the primary carriers. This disease can also be transmitted through indirect means such as arthropods, mosquitos and biting flies, but their rates of infecting humans with the disease are not as high.

The bacteria itself can enter the body through contact with the mucous membranes such as the eyes, mouth, throat, and lungs. It is worth it to note that human to human transmission of the disease seems impossible.

The symptoms shown by an infected person are dependant on the transmission vector, but all variations of the disease induce a high fever.

Wells disease is a rare development of leptospirosis where several more severe symptoms emerge. these symptoms are as follows:

jaundice
swollen ankles, feet or hands
chest pain
meningitis
encephalitis
coughing blood