Animas High School is warning students and parents of a case of mononucleosis at the school.

The school found out about the case among the student body Tuesday and plans to take preventive steps, such as extra-diligent cleaning, to prevent the illness from spreading, Principal Sean Woytek said.

Mono can cause symptoms such as high fever, a severe sore throat, weakness, fatigue and swollen lymph glands and tonsils, according to a letter sent by the school to parents. Weakness and fatigue from mono can last for weeks or months. Severe cases of mono can cause swelling of the spleen.

Teens and young adults are most likely to experience symptoms of mono. Between 35 and 50 percent of adolescents who are infected by mono develop symptoms, according to the letter by Etoile Hening, Animas High’s health consultant.

Symptoms can appear four to six weeks after an individual is exposed, she wrote.

The illness is generally spread through contact with saliva, mucus and sometimes tears.

Patients with mono can limit its spread by not kissing anyone, not sharing drinks or utensils and not sharing toothbrushes, the letter said.

Animas High asks students not to attend school until they have been free of a fever for at least 24 hours, without using any fever-reducing medications, according to the letter.

The school sends out similar letters to parents whenever a contagious condition is found among the student body, so its spread can be prevented, Woytek said.

“We want to be proactive,” he said.

mshinn@durangoherald.com