Friday, November 29, 2013

Worms in Nicaragua

Worms in Nicaragua

Worm disease is common in Nicaragua. One study showed Ascaris infection in 13% of individuals.

Worms are present worldwide in the moist warm soil found in the tropical latitudes. There are three common worms, Ascaris lumbricoides, Trichuris trichiura (whipworm), and Anclostoma duodenale & Necator americanus (hookworm).
 Ascaris eggs on R & L. Adult female in center. Images courtesy CDC.

Ascaris live in the lumen of the small intestine. A female can produce approximately 200,000 eggs per day, which are passed with the feces. Fertile eggs are infective after 18 days to several weeks, depending on the environmental conditions. After infective eggs are swallowed, the larvae hatch, invade the intestinal mucosa, and are carried via the blood to the lungs. The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed. Upon reaching the small intestine, they develop into adult worms. Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female. Adult worms can live 1 to 2 years.
Hookworm larva. Images courtesy CDC.

Hookworm eggs are passed in the stool, and the 
larvae hatch in 1 to 2 days. The larvae are infective after 5 to 10 days, and can survive 3 to 4 weeks. On contact with the human host (bare feet), the larvae penetrate the skin and are carried through the blood vessels to the heart and then to the lungs. They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed. The larvae reach the small intestine, where they mature into adults. Adult worms attach to the intestinal wall with resultant blood loss. Most adult worms are eliminated within 1 to 2 years.
Whipworm eggs on R & L. Adult female in center. Images courtesy CDC.

Whipworm eggs are passed in the stool, and the eggs are infective in 15 to 30 days. The eggs hatch in the small intestine and release larvae that mature and migrate to the colon. Female worms in the cecum shed between 3,000 and 20,000 eggs per day. The lifespan of an adult is about 1 year.

Once infected with a worm, a child can develop abdominal pain and distension, intestinal obstruction, iron-deficiency anemia, malnutrition and poor growth, and allergic reactions.

Mebendazole kills the worms. Mebendazole is on the World Health Organization (WHO) List of Essential Medicines for Children, and is intended for the use in children up to 12 years of age. There is limited data on the safety in children under the age of 2 years. In Nicaragua, a government program is in place to administer the medication. Each school-aged child receives a 500 mg dose of mebendazole. Reinfection is common, so the medication needs to be re-administered. 

Prevention is preferable to regular re-administration of the medication. 
The fundamentals of prevention for all worms include access to clean water, modern sanitation to dispose of infected feces, good personal hygiene with regular hand washing, and careful cleansing of soil-grown-vegetables and fruits.

To prevent hookworm infection, individuals should not walk barefoot in the soil and should otherwise avoid skin contact with soil.

Friday, November 22, 2013

Parasites in Nicaragua

Parasites in Nicaragua

Intestinal parasites in Nicaragua are endemic and contaminated water is the most common source. The common parasites include Entamoeba histolytica, Giardia lamblia, and Cryptosporium species. 

In one recent study, 53% of tested wells in Nicaragua contained amoeboflagellates. A study of 480 apparently healthy individuals in Leon, Nicaragua reported that Entamoeba histolytica or Entamoeba dispar was present in 12% of stool specimens. Another study found that Entamoeba histolytica or Entamoeba dispar was present in 19% of individuals and that Giardia lamblia was present in 16%. These percentages are high enough, that all rural children who drink well water should be presumed to have parasites in their intestine.

Infection by Giardia lamblia occurs by ingestion of mature cysts from fecally contaminated food, water, or hands. Swallowing as few as 10 cysts is enough to cause illness. The cysts are hardy and can survive several months in cold water. The symptoms of giardiasis normally begin 1 to 3 weeks after a person has been infected.
Giardia lamblia trophozoites L & R images, cyst in center. Images courtesy of CDC.

Infection by Entamoeba histolytica occurs by ingestion of mature cysts in fecally contaminated food, water, or hands. Although Entamoeba histolytica is commonly found in the stool, the majority of individuals are not symptomatic, but are potential carriers (able to transmit parasite but not symptomatic). About 10% of individuals develop amoebic dysentery. Amoebic dysentery has a gradual onset with watery or bloody diarrhea, crampy abdominal pain, and poor appetite and weight loss. Liver abscess is a possible complication. The infection is more common and more severe in malnourished children. 
Entamoeba histolytica trophozoites with ingested red blood cells. Images courtesy CDC.

Amoebic dysentery and giardiasis are treated with metronidazole. Unless the source of the infection is eliminated, many individuals will be re-infected after treatment. 

Prevention is therefore important. To prevent infection, the contaminated water source needs to be eliminated or the water needs to be treated. Drinking only bottled water is a good idea but might be too expensive for the average Nicaraguan family. Water can treated in a variety of ways shown in the table below. Careful hand washing and cleaning uncooked vegetables and fruits with clean or treated water is important.

1 micron

Entamoeba histolytica
Giardia lamblia
Cryptosporidium species

For chemical disinfection, two drops of bleach per liter of water is sufficient. Let the treated water stand for at least thirty minutes. Chemical disinfection is not sufficient for Giardia lamblia or Cryptosporidium

Not all filtration systems work for Cryptosporidium. A filtration system is adequate for Cryptosporidium only if the description includes one of the following three statements - reverse osmosis, absolute pore size 1 micron or less, or tested and certified by National Safety Foundation (NSF) Standard 53 or 58 for cyst removal.

Solar Irradiation is a promising method but the Centre for Disease Control (CDC) does not comment on effectiveness for parasites. There are emerging studies that do report effectiveness. 

Sunday, November 17, 2013

Bacterial Gastroenteritis in Nicaragua

Bacterial Gastroenteritis in Nicaragua

Montezuma's Revenge, typically caused by Entertoxigenic E coli (ETEC), is well known to travellers to Central America. The bacteria is a home grown problem too. In a 1997 study of infants in Leon, Nicaragua, ETEC were the cause of 38% of diarrhea episodes. 

Enterotoxigenic E coli, courtesy of Stanford Medicine.

There are many other bacteria that cause bloody diarrhea and abdominal cramps. The table below lists the more common causes.

Possible Source
meats, seafood
dairy, meats, poultry 
2 to 4
Cholera (Vibrio)
0 to 1
Tetracycline, Sulfa/Trimeth
E coli

1 to 3
Sulfa/Trimeth Quinolone
Enterhemorrhagic E coli
1 to 8
20 hrs
Ampicillin Sulfa/Trimeth
dairy, eggs, meats
0 to 3
Ampicillin Sulfa/Trimeth Quinolone

0 to 2
Ampicillin Sulfa/Trimeth Quinolone
Staph aureus
dairy, meats
2 to 6 hrs

0 to 6
Sulfa/Trimeth Quinolone

The "Possible Source" column clarifies why I avoid dairy (milk, cheese, yogurt, ice cream) and why I am very fussy about meat when I travel.

These bacteria include some of the classic tropical diseases such as Cholera and Typhoid (Salmonella). Shigella is one of the famous causes of dysentery in the tropics. Enterhemorrhagic E coli is the cause of Hemolytic Uremic Syndrome (Hamburger Disease), which was a huge part of my clinical life several decades ago when I was the Head of Paediatric Nephrology at the University of Calgary.

Most bacterial infections have a incubation period that lasts a few days. The exception is food poisoning with Staph aureus, which only requires a few hours of incubation. I experienced Staph aureus food poisoning in 1978 when I was competing in a 505 (international class two-man sailboat) qualifying event in Rhode Island. The local club prepared ham, cheese, and mayonnaise sandwiches for lunch and the fleet was on the water for about 6 hours. Within a few hours of eating I was nauseous and started to vomit. That day I crewed for one of Canada's Olympic Team. He didn't eat the sandwiches and he didn't get sick. My performance suffered, and he was not patient with me. On one tack I came in off the trapeze and kicked a new and very expensive watch off his wrist. A full gale blew in and we reduced sail and limped home. We finished twelfth in a fleet of about 80 boats. Four boats were lost in the gale. When we arrived back at the club, half the sailors were retching on the beach or on their way to the local hospital. I realized that we all had Staph aureus food poisoning, which is a self limited illness, so I rested on the beach, drank lots of fluids, and the episode passed as an interesting memory.

My personal preparations for the winter trips to Nicaragua will include booster immunizations for Typhoid and Cholera. While in Nicaragua, I will avoid dairy and only eat meat that I either cook or that is prepared by someone I trust.

To help treat bacterial gastroenteritis in Nicaragua, I will bring all of the medications in the list above, except Tetracycline, which is contraindicated in children.