There are all sorts of ways to get an infectious disease. They can pass from person to person. Insect or animal bites can transmit disease. Infectious diseases are also acquired by eating contaminated food or drinking dirty water, or being exposed to harmful organisms in the environment. 

These diseases can be caused by bacteria, viruses, parasites and other micro-organisms.

Yale Medicine has a skilled team dedicated to testing, diagnosing and treating infectious diseases, ensuring that patients get the best possible care.

One of the most common infectious diseases is the seasonal flu. Symptoms last about seven to 10 days, then resolve on their own. The flu, like many infectious diseases, can range from mild to severe.

"Depending on the individual, it could be a more mild presentation of a couple days, just body aches and fever, up to and including complications like pneumonia, depending on the strain,” says Christine Ngaruiya, MD, assistant professor of global health and international emergency medicine in the Department of Emergency Medicine at Yale Medicine. “Also it depends on the patient's general health status.”

Other common infectious diseases in the United States include pneumonia, urinary tract infections and meningitis.

Due to concern over the Zika virus, which first emerged overseas but has been reported in the continental United States, travelers, especially pregnant women and women who wish to become pregnant, are urged to avoid visiting places where Zika virus is prevalent.

Signs that a patient should seek treatment include:

• Fevers that cannot be controlled at home with over-the-counter medications
• Vomiting and/or extreme diarrhea, which will put you at risk for dehydration, or inability to tolerate oral intake
• Severe headache
• Severe shortness of breath

Patients who have traveled to such high-risk areas as West Africa during the Ebola epidemic, or South America and parts of Southeast Asia since the emergence of the Zika virus, should be especially alert to those symptoms.

"If you’re coming back from an affected area and you have a fever, you should be evaluated by your provider for the source of the infection,” Dr. Ngaruiya says.

Yale Medicine has a triage system to gauge how sick a patient is and to determine whether he or she needs immediate attention. Specialists then determine whether precautions must be taken to quarantine the patient from other patients or providers.

"Providers will talk to you about your symptoms and risk factors based on the rest of your history, travel behaviors or possible exposures,” says Dr. Ngaruiya.

For the most common viruses, Yale Medicine can administer noninvasive diagnostic tests, including nasal swabs, that can pick up some types of the flu. Blood tests can identify specific viruses or infections and cultures can grow the type of bacteria that’s being assessed. Specialists can check stool samples, especially for some of the parasites and types of bacteria that primarily affect the gut.

“We also have immunological types of tests where the specialist can assess for evidence of the bug from the person's blood or other body fluid,” says Dr. Ngaruiya.

There is now a blood and urine test available for Zika virus.

Infectious diseases are usually transmitted by contact with body fluids, including blood, sputum, semen, or vaginal secretions, and mucus membranes—the eyes, mouth, or nose.

While some infectious diseases can be passed in this way from person to person, others may be transmitted by bites from insects or animals. Others may be acquired by drinking or eating contaminated food or water.

An incubation period is the duration of time when an infection is in the bloodstream or in the body and replicating to a point where the infected person develops symptoms. This time varies according to the disease.

“For example, with Ebola, the incubation period is up to 21 days,” says Dr. Ngaruiya. "With Zika, unfortunately, we don't have a great understanding of it because the majority of patients present with only mild symptoms that might be written off.”

The incubation period is important because patients may not know that they have a disease until they’ve spread it to somebody else, or they may never know that they have the disease.

"It's easy to miss, so it's hard to study a disease when the majority of patients don't even know that they're sick,” Dr. Ngaruiya says. “That's why these diseases have been so effective in spreading so rapidly.”

A number of vaccines are available to prevent infectious diseases, including those for hepatitis A and hepatitis B, depending on where you go, says Dr. Ngaruiya. “You might also get what’s called a meningococcal vaccine, to prevent a certain type of bad meningitis infection that is most prevalent in certain parts of Sub-Saharan Africa."

Malaria prophylaxis (medications taken just before or during and after the travel) is also available.

Practicing safe sex is essential, because HIV and other sexually transmitted diseases are even more of a problem in many international settings, Dr. Ngaruiya says.

Regarding the mosquito-borne Zika virus, a few cases of transmission through insect bites have been reported in the United States. The majority of those who have contracted the disease in the United States have been health care providers or someone who has been in intimate contact with an infected person’s body fluids, Dr. Ngaruiya says.

To have been exposed to Ebola, a person needs to have been at an endemic or epidemic outbreak site.

Patients who have been to an affected location would undergo a 21-day observation period just to make sure that they don't develop symptoms.

“With regards to Ebola and Zika, we're recommending safe sexual practices because again, the disease is transmitted sexually,” says Dr. Ngaruiya. “Especially in the case of Zika, since it’s particularly detrimental to an unborn fetus.”

Pregnant women, or women trying to become pregnant, should follow CDC guidelines and avoid traveling to affected regions, says Dr. Ngaruiya.

While traveling to affected areas, Dr. Ngaruiya suggests:

• Wear protective clothing as much as possible. If you're going on hikes or into very rural areas, tuck in clothing, and tuck pant legs in boots.
• Apply Permethrin, an insect repellent, to clothes and then spray DEET or Picaridin on top of that.
• Close windows and make sure there are shields along windows and doors that bugs cannot get through.
• Bed nets can also keep mosquitoes away at night.

“Prevention is better than cure with these cases,” Dr. Ngaruiya says.

Depending on the disease, a patient may be treated with antibiotics, antifungals, antivirals, or antiparasitics.

That said, not every disease has a treatment, and the severity of infectious diseases varies. Mild infections may improve with rest, while some life-threatening infections may require hospitalization.

“Viruses are very elusive, and there are no cures for Zika or Ebola,” says Dr. Ngaruiya. “It's about being safe before you go and then, if you are to develop symptoms, seeking care early and, in the case of Zika, evaluation of the fetus if you become pregnant.”

At Yale Medicine, there’s an entire team dedicated to treating infectious disease.

“As an academic center, we're definitely at the forefront with any testing, treatment and diagnostics with these diseases,” says Dr. Ngaruiya.

Patients fearing that they’ve been exposed to an infectious disease should feel secure that Yale Medicine is prepared to deliver extraordinary care. “We have all the tools necessary to handle a case,” Dr. Ngaruiya says.