4.8 Chemoprophylaxis, Malaria.& Insect-borne Diseases

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8. Chemoprophylaxis (CP) –update 15 Aug. 2021

ChemoProphylaxis is medicine for prevention. I focus on CP against infection. The following descending column of topics are found in order of reading text.

Antibiotic Contra Infection    
 Amoxicillin

Metronidazole (Flagyl)

Augmentin

Clindamycin

Anti-Malaria CP
mosquito bites
prevention 

Dengue Fever
New Dengue Fever Vaccine

Japanese Encephalitis

West Nile Fever 
Tick bites

   Antibiotic Contra Infection: At early stage, with few germs, an antibiotic may eradicate infection before it takes hold. Even when CP seems successful, it is uncertain whether, for other reason, one did not catch the infection to be prevented by CP.  So CP should have a wide margin of safety and be used mainly against serious, hard to cure infection.

   Timing is crucial. Take CP within half hour of the infecting event; best just before. Frequently used just before surgery.

   Amoxicillin lends itself as CP antibiotic: its low toxicity allows big single dose (3.5 g); its broad-spectrum effect covers wide range of bacteria (Even bacteria normally “resistant” to Amoxi may be undone by high blood level single dose, when the bacteria are localized or few); also easy to get and inexpensive (Buy generic). As Sexually Transmitted Disease preventive, take shortly before or immediately after sex encounter. (Always use condom as first line defense) Adding 2g of metronidazole (Flagyl) to the Amoxi will prevent infection by trichomonas, which makes smelly, itchy vaginitis in women, and makes male partner(s) into carrier(s); and it will prevent some common GI and urinary tract germs. Even better than Amoxi itself is Augmentin, which is Amoxi plus Clavulinic Acid.

   I do not advise every person having sex should gulp pills. But there are times when it is useful. Rape comes to mind. Also, high-risk sex encounter!

    A recent addition to my CP antibiotics is Clindamycin: start with six and then continue the six 150 mg capsules every 6 hours for 48 hours. It is powerful broad-spectrum. Just before surgery even higher dose (Longer treatment has a risk of dangerous drug resistant diarrhea)

Anti Malaria CP is location-specific when you enter malaria area. Typical symptom is sudden high fever with chattering teeth. Infected mosquito transmits it. In Central and North America, malaria only exists south of the Rio Grande River.  In Latin America it has been eradicated from Argentina and Uruguay. In Africa it is widespread except for Morocco and South Africa. In Middle East, it is eradicated from Israel only. Malaria still exists in India and SE Asia including Indonesia. But Japan has none and China only in its southeast. The Philippines has it but not in Manila.

   A mosquito bites a human to obtain a blood meal; the malaria germ from an infected mosquito enters the victim's blood and lodges in liver for several weeks. Each germ produces thousands of offspring that flood the blood at 1-to-3-day intervals causing typical attack of high fever. The malaria germ destroys red blood cells producing the worst anemia on record. (A 4-gram/dL hemoglobin [normal 12-gram/dL] anemia in a case that survived.) Depending on the malaria germ type and human host immune response, an infected person may die of brain malaria or become subject to repeat high fever that results in victim wasting away in ill health.

   First line of prevention is avoid visit to malaria area. No malaria immunization exists and medicine against malaria is imperfect so, unless you have important reason to travel to malaria area, why risk lifelong infection? In planning foreign trip call U.S. CDC Malaria Hotline at 1-770-488-7788. (Checked recently and got after hours announcement and may leave question and will get rapid answer; for those who wish to consult on a malaria case, digit 1 770 488 7100.) The hotline can tell you what area and country is malaria risk, and what CP is advised for particular area.

   If you must visit malaria area, the next line of prevention is to avoid mosquito bites. The hour before dusk and after dawn is peak time, but it may be any time so use an insect-repellent net when you sleep, use clothing that allows minimum skin exposure, and rub or spray DEET repellent onto exposed skin before going out.

   No chemical drug for prevention of malaria illness is ideal. Since 2017 Coartem is advised. But traveler to Mexico and Central America or Egypt and the Middle East is still advised to use chloroquine. (Check it on the CDC hotline.)

Dengue Fever is a mosquito-bite fever common in Philippines and SE Asia and India. (Flash! Nov. 2015! Dengue fever case in Hawaii!)  It has no treatment but is mentioned here because, like malaria, it is passed on by the bite of a mosquito. It is high fever for several days and cures itself but also often drops the blood platelet count 50,000 or below and that poses risk of bleeding and if below 20,000 may end up being treated with platelet transfusions. This could be important in place like the Philippines where risk of HIV contaminated blood is high. If I had dengue fever in the Philippines I would immediately fly to USA or Japan or Europe, wherever closest best care. Even very low platelet count (10,000) is not immediate high risk but one must take precaution of no aspirin and no NSAID, no high risk of trauma like bicycle ride, and eat a bland anti-ulcer diet, and, of course, quickly get to modern, adequate healthcare facility.
Flash! Latest Dengue Fever Vaccine (CYD-TDV) is a live, attenuated dengue virus that is given in 3 shots at 0, 6 and 12months with about 80% protections and is currently available in Indonesia, Mexico and Philippines. It is only for foreign guests or workers in a country that has endemic Dengue Fever mosquitoes. 
   Other mosquito bite diseases are Japanese Encephalitis (Prevented by immunization; see Chapter 4.2), West Nile fever and other encephalitis.  West Nile fever is recently spread in New York & Texas. It’s only prevention is avoiding bites as above. 
   Ticks are grass insects. Tick bites are around the feet and may cause Lyme disease (prevented by immunization but latest is that it has been discontinued because of low demand) and encephalitis. Always have skin well covered when you hike. Diagnosis is easy blood test and treatment is 4 weeks tetracycline by mouth antibiotic.  Tick bites in the Russian Far East cause spring-summer encephalitis. Workers in lumber industry there may get preventive immunization.

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