Physicians & Staff


Ryan Welter

Ryan Welter, MD, PhD

Board Certified Family Practice
Neonatal Advanced Life Support Certified
Advanced Obstetrics Life Support Certified

Dr. Ryan Welter received his medical degree from the University of Oklahoma and graduated from Brown University’s Family Medicine Residency Program. He is board certified in family practice and has training in obstetrical and neonatal life support.

Before completing medical school, Dr. Welter finished a doctoral thesis in biochemistry and molecular biology at Oklahoma State University where he focused on lipid biochemistry.

Dr. Welter has been providing care in Massachusetts at St. Anne’s Hospital in Fall River, and Mediplex Rehab Hospital in New Bedford for several years. His most recent appointment is at Morton Hospital in Taunton where he maintains private practice. Devoted to excellence in patient care, Dr. Welter believes in treating patients as individuals, taking into account the person, not just the illness. He believes in devoting time to patient education and will strive for nothing less than superior medical supervision. Dr. Welter believes in the concept of family medicine. He is a devoted husband and father of eight. As a board certified family practitioner he is qualified to treat all your family’s health problems from routine exams to in-office surgeries and routine obstetrical care.


Brett Stecker Brett Stecker, D.O.

Dr. Stecker received his medical degree from New York College of Osteopathic Medicine in Old Westbury, NY and completed his residency at Brown University’s Family Medicine Program. He is board certified in Family Medicine and has a special interest in Sports Medicine. Dr. Stecker enjoys taking care of entire families and believes that through positive interaction with each individual family member.

Brown Medical LogoDr. Stecker devotes time to continuing medical education, reading recent journal publications, and remaining current with the rapidly changing world of medicine to bring the best care home to his patients. In addition to his professional life, Dr. Stecker enjoys running, reading, cooking and spending time with his cats..


Kathleen O'Callahan Woodworth Kathleen O’Callahan, ANP-C

Kathy joined Welter Primary Care in 2004, following a distinguished career in nursing. She received an adult Nurse Practitioner Masters degree at the University of Massachusetts, seeing patients age 13 and older. Her undergraduate degree is an RN-BSW degree earned from the Children’s Hospital School of Nursing (Curry College).

Her employment experience includes the VA Hospital, Mass Eye and Ear Infirmary, Faulkes and Brigham Women’s Hospital and home health care. This diversity of experience includes emergency assessment and management, orthopedics, ophthalmology, ENT and optimized management of chronic disease. Kathy’s goal is to provide superior care while making a positive difference in her patients’ lives.

The mother of four, Kathy balances personal passions for music, dance and spending time with enjoyable family and friends with her professional mission of health maintenance education. She believes that an individual’s understanding of illness, disease and medical interventions will promote self care, and the maintenance and stability of their health.


Yvonne Rizk, MD

Yvonne graduated with a degree in Preliminary Natural Science from University of Khartoum- Sudan and received her medical degree from Faculty of Medicine University of Khartoum – Sudan. Dr. Rizk trained in Anatomic and Clinical pathology at the Brown University affiliated program and was certified by the American Board of Pathology in 1994. She held the positions of Clinical assistant Professor at Brown University and Adjunct professor of clinical Laboratory Science, Department of Biochemistry and Molecular genetics at the University of Rhode Island in addition to being a Staff Pathologist at Women and Infants Hospital of Rhode Island from 1992 to 2001. Dr. Rizk trained in Pain management from 2002 to 2005 and became a Diplomate of the American Academy of Pain management in 2002 and was the Proprietor of the Pain care center in N. Dartmouth from 2005 to 2008. Dr. Rizk joined Welter Primary Care in 2008 and is now the Director of Pain Management.

Paul Keefe, MD

Dr. Keefe graduated from the University of Massachusetts Medical School and received his undergraduate degree from the University of Notre Dame.  He has been Medical Director NSTAR, National Grid and Jordan Hospital Occupational Health.

Dr. Keefe is a Diplomate of the American College of Internal Medicine.  He is also a Certified Medical Review Officer (MROCC). Dr. Keefe currently provides occupational health care as Medical Director at Tristan Medical in Avon.

Jacquelyn Desjardins, PA-C


Jacquelyn is a stand-out graduate of MCPHS University in Boston, MA. She has had extensive training at distinguished facilities including Spaulding Rehabilitation Center, Tufts Medical Center, Boston Medical Center, Massachusetts General Hospital, and Newton Wellesley Hospital.  Prior to graduate studies, Jackie attended UMass Amherst, where she majored in psychology neuroscience, in addition to completing pre-medical track courses.  She also worked four years in the operating room at Baystate Medical Center in Springfield.

Jackie believes in treating the whole patient and strives to make patient education a primary focus, in addition to maintaining up to date practices in the evolving medical field.

She lives in the area and enjoys music, movies, and sports.

Terri A Sullivan, RN, MSN, FNP-C

Terri joined Welter Primary Care in 2010 after working at Morton Hospital in Occupational Health Services for five years.  Terri received a Baccalaureate Degree, Nursing Cum Laude from Northeastern University in 1985 and a Masters of Science as a Family Nurse Practitioner from University of Massachusetts in Boston.

Terri is an accomplished FNP-C and has worked in healthcare for the last three decades as a Clinical Instructor for nursing, Clinical Director for Morton Hospital and Nurse Practitioner for Occupational Health Services for several years.Terri’s goal is to provide the quality healthcare and the ability to get someone back on their feet and working.

Charles Davis Leah Callan, ANP-BC

ANCC-certified Adult Nurse Practitioner

Masters of Science in Nursing, UMASS Dartmouth, Dartmouth MA Diploma RN, Brockton Hospital School of Nursing, Brockton, MA Bachelor’s Degree Biology with minor Chemistry, Stonehill College, N. Easton, MA

14 years experience as nurse practitioner in urgent care, internal medicine, geriatrics, family practice Aesthetic training in Laser, Botox and fillers Medically Supervised Weight Loss Guest lecturer and preceptor, Northeastern University, UMASS Dartmouth, UMASS Boston

11 years experience as critical care nurse, including supervisor 4th busiest Emergency Department in MA, Board-certified Emergency Nursing.

Professional affiliations: Massachusetts Coalition of Nurse Practitioners, Member, Executive Committee Former Co-chair legislative Committee and PR and Marketing Committee Sigma Theta Tau

Awards: MCNP Outstanding Preceptor Award 2007 MCNP Award for Legislative Advocacy 2006

Sue SullivanSusan Sullivan, MHP, PA-C

Susan Sullivan completed her graduate degree at Northeastern University. She completed her undergraduate degree at Stonehill College graduating summa cum laude with a BS in biology.

Susan’s past experience as a physician assistant has been in both internal medicine and urgent care.  She has worked in healthcare for more than thirty years.

Susan’s goal is to provide her patients with superior preventative medical care in order to improve the quality of their lives presently and in the future.


Dennis Teehan, M.D. MPH

Dr. Dennis Teehan comes to Tristan Medical by way of Tufts Medical School where he earned his M.D. He completed a residency in Preventive Medicine at Harvard. He has experience in urgent care, primary care, preventive medicine and occupational medicine. He also has earned a Master of Public Health Degree from Harvard University. He is expecting his first research publication on “Sudden Cardiac Death in Firefighters Under 45″ in the journal Cardiology this winter. His clinical interests include Nutrition, Exercise, Mind Body Medicine and Medical Hypnosis and the psychosocial aspects of health and wellness. Dr. Teehan believes in providing compassionate, clinically effective care to all patients and places emphasis on weighing the risks and benefits of every medical treatment carefully. He believes that fitness, nutrition, healthy sleep and good relationships are the cornerstones of a healthy life. He is a member of the American College of Physicians, The American College of Occupational & Environmental Medicine, The American College of Preventive Medicine and the Urgent Care Association of America. In his personal time Dr. Teehan’s hobbies include running, physical fitness, writing and playing guitar. He is a long time season ticket holder for the New England Patriots.

Kaleigh McA’Nulty, PA-C

Kaleigh is a member of the Primary Care team at our office in Raynham. She completed her graduate studies at Massachusetts College of Pharmacy and Health Sciences in Manchester, New Hampshire in 2012. Her bachelor’s degree is in engineering from Tufts University, and following her undergraduate career she worked in a group home for adults with mental illness and developmental disabilities and in a retail pharmacy before pursuing her training in clinical medicine. She has particular interests in preventative medicine, women’s health, and mental health and enjoys working with her patients to develop habits that will lead to a happy, healthy life.