Neisseria meningitidis is a bacterium that causes a potentially fatal infection with sepsis or meningitis. There are five common serogroups that cause disease in humans (A, B, C, Y, & W-135). It is acquired by close person-to-person contact via aerosol or mucous secretion exchange. Although there are sporadic cases of meningococcal disease in the US (usually in children and young adults) it is endemic in sub-Saharan Africa, particularly during the dry season (December through June) and may be epidemic in parts of East Africa, northern India and Nepal at any given time. It is important that the traveler be aware of updated advisories regarding meningococcal disease activity in these and potentially other areas of the world.
The meningococcal vaccine is very effective in preventing disease. It is prepared from capsular polysaccharides from serogroups A, C, Y, and W-135 (the B capsular polysaccharide is non-immunogenic). Meningococcal vaccine is not required for entry into any country, but it is required for pilgrims going to Mecca, Saudi Arabia for the annual Hajj. The vaccine is well-tolerated and is given as a single subcutaneous dose that is effective for at least three years.
Hepatitis B Virus (HBV)
Viral hepatitis B is the most important infectious cause of acute and chronic liver disease in the U.S. and worldwide. Chronically infected persons are at risk of long-term sequelae, including chronic liver disease and hepatocellular (liver) cancer. Although there are estimated to be 750,000 to 1,000,000 HBV carriers in the U.S., the disease burden due to HBV infection worldwide is even higher due to the occurrence of almost universal infection during infancy and early childhood in most of the developing world. In most countries in Asia and Africa, between 5% and 20% of children and adults are HBV carriers. HBV is the second most prevalent vaccine-preventable infection in non-immune travelers occurring in 800 to 2400 cases per 100,000 non-immune travelers, with a mortality rate of 16-48 per 1,000,000 non-immune travelers per month. Travelers can acquire hepatitis B via sexual or other physical contact as well as exposure to blood or body fluids. One third of cases have no recognized risk factors. Travelers at greatest risk have been shown to be those living overseas longer than six months, particularly those with close personal contacts in high prevalence areas.
Two types of hepatitis B vaccine have been licensed in the U.S.: two recombinant vaccines produced in yeasts, and one human serum-derived from the plasma of chronically infected persons. Currently only the recombinant vaccines are available, since production of the serum-derived vaccine was discontinued in 1989. There is no risk for transmitting infections with the current recombinant vaccines. These vaccines, when used in the recommended series of three intramuscular doses induce a protective antibody response in > 90% of healthy adults ages 20-39 years. The response rate in healthy adults decreases with advancing age: there is a 70% response in adults 50-59 years old and only 50 to 80 % in those 60 years or older. Other factors that decrease vaccine response include chronic diseases, HIV infection, obesity, and smoking. The duration of vaccine-induced immunity with the serum-derived vaccine has been shown to be at least 9 years in follow-up studies of both adults and children.
In the U.S. hepatitis B vaccination is recommended for all infants and selected high-risk groups, which includes international travelers. HBV vaccination is recommended for travelers who plan to spend more than 6 months in areas with high rates of HBV infection and who will have close contact with the local population. Short-term travelers who are likely to have contact with blood or to have sexual contact with the local population in areas with high or intermediate levels of endemic disease should also be immunized. Vaccination should be begun at least 6 months before travel to allow for completion of the full vaccine series, although a partial series may offer some protection.
Sexually transmitted infections (STI)
STIs are hyperendemic in many developing countries: in addition to HIV, at least 333 million new cases of other STIs occurred in 1995 (WHO, 1996). Surveys of short-term travelers as well as long-term overseas workers reveal significant sexual contact with host country nationals, often with prostitutes and without barrier (e.g. Condom) protection. It is currently estimated that there are over 30 million HIV infected humans worldwide. HIV is highly endemic in many Third World countries, particularly in parts of Africa, S.E. Asia, and among sex workers. Barrier contraceptive devices (condom), provide the best alternative to abstinence in preventing HIV transmission by preventing direct contact with infective genital lesions or secretions.