Epidemiology & surveillance - NTDs_SP_11.12.23_REVISION (2).pptx

Epidemiology & surveillance of neglected tropical diseases Dr Stavros Panagiotou Neglected Tropical Diseases (NTDs) • NTDs are a diverse group of 20 conditions that mostly affect impoverished communities in tropical areas of the world • One billion people affected – health, social & economic burde...

Epidemiology & surveillance of neglected tropical diseases Dr Stavros Panagiotou Neglected Tropical Diseases (NTDs) • NTDs are a diverse group of 20 conditions that mostly affect impoverished communities in tropical areas of the world • One billion people affected – health, social & economic burden • 149 countries affected (often co-endemic) • Morbidity rather than mortality • Disproportionately affect women and children https://www.who.int/health-topics/neglected- Epidemiology of NTDs • Complex – often related to environmental conditions • Many are vector-borne, have animal reservoirs and are associated with complex life cycles • Many are preventable through vector control, improved water quality & sanitation and drug treatment https://www.who.int/healthtopics/neglected-tropical-diseases Brugia malayi Brugia timori Wucheria bancrofti Lymphatic filariasis Onchocerca volvulus River blindness Schistosoma spp. Schistosomiasis Helminth NTDs Trichuris trichiura Trichuriasis Ascaris lumbricoides Ascariasis Ancyclostoma duodenale Necator americanus Hookworm infection Echniococcus granulosum Echinococcosis Schistosomiasis • Infection occurs when larval forms of the parasite – released by freshwater snails – penetrate the skin during contact with infested water. • Transmission occurs when people suffering from schistosomiasis contaminate freshwater sources with their excreta containing parasite eggs, which hatch in water. • In the body, the larvae develop into adult schistosomes. Adult worms live in the blood vessels where the females release eggs. • Some of the eggs are passed out of the body in the faeces or urine to continue the parasite’s lifecycle. Cercariae (human infective stage) Part of life cycle completed in sna Diagnosis through the detection of parasite eggs in stool or urine specimens Epidemiology It is estimated that at least 90% of those requiring treatment for schistosomiasis live in Africa. Epidemiology & Symptoms Abdominal pain, diarrhoea, and blood in the stool. Liver enlargement and splenomegaly is common in advanced cases Haematuria (blood in urine). Fibrosis of the bladder and ureter, and kidney damage are sometimes diagnosed in advanced cases. Bladder cancer is another possible complication in the later stages. Genital lesions Schistosomiasis diagnosis • Detection of eggs in faeces or stool • However, eggs can be passed intermittently and in small amounts so may not be detected • Serology Schistosomiasis control • Large-scale treatment of at-risk population groups (praziquantel), access to safe water, improved sanitation, hygiene education, and snail control. • Estimates show that at least 236.6 million people required preventive treatment for schistosomiasis in 2019, out of which more than 105.4 million people were reported to have been treated. • Eradication in 40 countries Filarial nematodes Brugia malayi Brugia timori Wucheria bancrofti Lymphatic filariasis Onchocerca volvulus River blindness Lymphatic filariasis ~157 million people infected with LF parasites • Causitive agents include the mosquito-borne filarial nematodes Wuchereria bancrofti (90% of cases), Brugia malayi, B. timori • Symptoms: severe lymphedema of the limbs (“elephantiasis”) and occasionally genitalia (hydrocele) due to dysfunction of lymphatic vessels. • Affected limbs become grossly swollen; the skin may become thick and pitted, and secondary infection are frequent due to lymphatic dysfunction. • This leads to social stigma, as well as financial hardship from loss of income and increased medical expenses • Lymphangitis, lymphadenopathy, and eosinophilia may accompany infection in the early stages. Transmission of LF parasites • The typical vector for Brugia spp. filariasis are mosquito species in the genera Mansonia and Aedes. • W. bancrofti is transmitted by many different mosquito genera/species, depending on geographical distribution. Among them are Aedes spp., Anopheles spp., Culex spp. and Mansonia spp. An Anopheles gambiae mosquito taking a blood meal. Epidemiology of LF 73 countries affected, 120 million people infected, and 40 million incapacitated by the disease LF has been eradicated in • Togo • Maldives • Sri Lanka • Thailand • Cambodia • Egypt • Some pacific islands Epidemiology (cont.) • W. bancrofti is endemic in Sub-Saharan Africa (excluding the southern portion of the continent), Madagascar, several Western Pacific Island nations and territories and parts of the Caribbean. • Bancroftian filariasis also occurs sporadically in South America, India, and Southeast Asia. • Brugia spp. associated with LF are more geographically limited and occur only in Southeast Asia. Diagnosis of LF • Identification of microfilariae in a blood smear by microscopy (Giemsa stain or H&E) • Blood smear should be taken at night (nocturnal periodicity) • Serology: patients with active infection typically have elevated levels of antifilarial IgG4 in serum Prevention & Control • Programs to eliminate lymphatic filariasis are under way in more than 66 countries. • These programs are reducing transmission of the filarial parasites and decreasing the risk of infection for people living in or visiting these communities. • The elimination strategy is based on annual treatment of whole communities with combinations of drugs that kill the microfilariae. • Since these drugs also reduce levels of infection with intestinal worms, benefits of treatment extend beyond lymphatic filariasis. Treating patients with clinical symptoms • People with lymphedema and elephantiasis are unlikely to benefit from DEC treatment because most people with lymphedema are not actively infected with the filarial parasite. • To prevent lymphedema from getting worse, patients should ask their physician for a referral to a lymphedema therapist so they can be informed about some basic principles of care such as hygiene, elevation, exercises, skin and wound care, and wearing appropriate shoes. • Patients with hydrocele may have evidence of active infection, but typically do not improve clinically following treatment with DEC. The treatment for hydrocele is surgery. Onchoceriasis • Onchocerciasis can cause pruritus, dermatitis, onchocercomata (subcutaneous nodules), and lymphadenopathies. • The most serious manifestation consists of ocular lesions that can progress to blindness. • 20.9 million infections worldwide: 14.6 million of the infected people had skin disease and 1.15 million had vision loss Transmission • Transmitted by blackflies (Simulium spp.) • These blackflies breed along fast-flowing rivers and streams, close to remote villages located near fertile land where people rely on agriculture • Onchocerciasis occurs mainly in tropical areas. • More than 99% of infected people live in 31 countries in sub-Saharan Africa. • Onchocerciasis is also transmitted in Brazil, Venezuela and Yemen. Diagnosis of onchoceriasis • Skin snip – a 1 to 2 mg shaving or biopsy of the skin is done to identify larvae, which emerge from the skin snip and can be seen under a microscope when put in physiologic solutions (e.g. normal saline). • Typically six snips are taken from different areas of the body. • Polymerase chain reaction (PCR) of the skin snip can allow for diagnosis if the larvae are not visualized. • In patients with nodules in the skin, the nodule can be surgically removed and examined for adult worms. • Infections in the eye can be diagnosed with a slit-lamp examination of the anterior part of the eye where the larvae, or the lesions they cause, are visible. Treatment • Community-directed treatment with ivermectin at least once a year (for 10-15 years) is the core strategy to eliminate onchocerciasis in Africa. • Where O. volvulus co-exists with Loa loa, treatment strategies have to be adjusted due to adverse affects that can result from high Loa loa burden in the blood. • Four countries have been verified by WHO as free of onchocerciasis after successfully implementing elimination activities for decades: Colombia, Ecuador, Mexico, and Guatemala • 1.8 million people live in areas that no longer require mass drug administration for onchocerciasis. Soil-transmitted helminths Trichuris trichiura Trichuriasis Ascaris lumbricoides Ascariasis Ancyclostoma duodenale Necator americanus Hookworm infection Overview of STH infections • STH infections are transmitted by eggs present in human faeces, which contaminate the soil in areas where sanitation is poor. • Light infections are often asymptomatic. • Heavier infections can cause a range of symptoms including intestinal manifestations (diarrhoea and abdominal pain), malnutrition, general malaise and weakness, and impaired growth and physical development. Infections of very high intensity can cause intestinal obstruction that should be treated surgically. • More than 1.5 billion people, or 24% of the world’s population, are infected with STH infections worldwide. • Control is based on periodical deworming to eliminate infecting worms, health education to prevent re-infection, and improved sanitation to Trichuris eggs Ascaris eggs Hookworm larvae Mass drug administration (e.g. school health Nutritional effects • The worms feed on host tissues, including blood, which leads to a loss of iron and protein. • Hookworms in addition cause chronic intestinal blood loss that can result in anaemia. • The worms increase malabsorption of nutrients. • Some soil-transmitted helminths also cause loss of appetite and, therefore, a reduction of nutritional intake and physical fitness. • T. trichiura can cause diarrhoea and dysentery. Growth stunting Mass drug administration • The strategy for control of soil-transmitted helminth infections is to control morbidity through the periodic treatment of at-risk people living in endemic areas. • People at risk are: o preschool children o school-age children o women of reproductive age (including pregnant women in the second and third trimesters and breastfeeding women) o adults in certain high-risk occupations such as tea-pickers or miners. • Periodical treatment aims to reduce and maintain the intensity of infection, and to protect infected at-risk populations from morbidity. • Anthelminthic drugs: albendazole & mebendazole for 1-3 days Hookworm infection • An estimated 576-740 million people in the world are infected with hookworm. • Infection mostly asymptomatic. • Itching and a localized rash at site of infection (where larvae penetrate skin). • Growth stunting and anaemia in children (& pregnant women) with heavy worm burdens. Anterior of A. duodenale and N. americanus Skin penetration Highly magnified histologic section showing hookworm (Ancylostoma spp.) attached Ascariasis • 807 million–1.2 billion people infected. • Symptoms include abdominal discomfort or pain, and cough (due to migration of the worms through the body). • Migrating adult worms may cause symptomatic occlusion of the biliary tract, appendicitis, or nasopharyngeal expulsion. • Heavy infections can block the intestines and slow growth in children. Summary • Overview of neglected tropical diseases • Complex – often related to environmental conditions • Many are vector-borne, have animal reservoirs and are associated with complex life cycles. • Epidemiology & surveillance of: • Schistosomiasis, lymphatic filariasis, onchoceriasis & soil-transmitted helminths • Sleeping sickness, Chaga’s disease & leishmaniasis